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Why reapply your sunscreen every 2h?


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#1 Eva Victoria

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Posted 12 February 2008 - 05:22 PM


Since I have read several posts about this topic here on Imminst, I would like to post some studies for those who wonder what can happen when you don't reapply your sunscreen every 2h.
(UV-rays can damage your skin, so can they do the same to your sunscreen!)

Pls. see attachments.

Attached Files



#2 donjoe

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Posted 12 February 2008 - 09:48 PM

It's an important warning, so I'll mention it here as well: octocrylene, octylmethoxycinnamate and benzophenone-3 (oxybenzone) can cause more damage than if they hadn't been applied at all, as early as 1h after application (if not re-applied), according to this recent study.

Edited by donjoe, 12 February 2008 - 09:49 PM.


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#3 niner

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Posted 13 February 2008 - 07:31 AM

It's an important warning, so I'll mention it here as well: octocrylene, octylmethoxycinnamate and benzophenone-3 (oxybenzone) can cause more damage than if they hadn't been applied at all, as early as 1h after application (if not re-applied), according to this recent study.

can cause more damage than if they hadn't been applied at all... Wow, that's pretty disturbing, if true. The abstract only talks about ROS, but isn't there more to UV damage than ROS? For example, UV causes thymine-thymine dimers to form in DNA. There are probably other non ROS-mediated forms of damage, I'd think. This would at least seem to be a good argument for topical antioxidants.

#4 Live Forever

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Posted 13 February 2008 - 08:13 AM

I would suspect that UV would cause more damage than anything that any manufacturer would ever risk putting in a sunscreen. (for fear of being sued)

Generally, manufacturers (at least in the US, perhaps not other countries) err on the side of caution when it comes to consumer's health for that very reason.

#5 donjoe

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Posted 13 February 2008 - 12:37 PM

The abstract only talks about ROS, but isn't there more to UV damage than ROS?

Well, maybe there is, but at the 1h marker, after the sunscreen has been absorbed into the skin, I doubt that protection against those other types of damage is at its highest anymore - the very reason that ROS production increases so much is the photodegradation of those filters, so I think it's reasonable to assume that by that time there's almost no protection left to offset the effects of the increased ROS production. And that's bad.

I would suspect that UV would cause more damage than anything that any manufacturer would ever risk putting in a sunscreen. (for fear of being sued)

Generally, manufacturers (at least in the US, perhaps not other countries) err on the side of caution when it comes to consumer's health for that very reason.

In this case it's not about what the manufacturers put in the sunscreen, in the bottle, but about what happens to it after prolonged exposure. And more to the point, it's about how you use the sunscreen - in the case of the three substances above, you can re-apply every hour (and after bathing etc.) and you should be fine. (But something tells me most people would simply choose to buy something different.)

#6 Eva Victoria

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Posted 13 February 2008 - 04:05 PM

It's an important warning, so I'll mention it here as well: octocrylene, octylmethoxycinnamate and benzophenone-3 (oxybenzone) can cause more damage than if they hadn't been applied at all, as early as 1h after application (if not re-applied), according to this recent study.


I would like to add one thing here: it only applies to chemical sunscreens! Physical sunscreens : TiO2, ZnO do not penetrate the skin, their molecules are too big to be able to absorbed by the skin. ZnO2 has antioxidant properties in itself and TiO2 is proven to be stable on the skin: does not produce free-radicals.

Octocrylene is a veery good and stable filter that stabilizes Avobenzone and OMC and Avobenzone are stabilized by the Tinosorb filters. Hence when you use a sunscreen bought in the EU and made by L`Oreal group or Nivea you should not worry much. (See attachment).

The truth is also that no sunscreen ever can protect yourself as perfectly as avoiding the SUN; meaning IF you cannot stay inside, well protected from sunshine then the next best thing is SUNSCREENS.

It is fully proven that sunlight in it self damage the skin even when you wear a sunscreen, so avoidance is nr 1 priority!

avobenzone: Information
http://www.answers.c...?cat=technology

http://www.patentsto...1-fulltext.html

Attached Files


Edited by Eva Victoria, 13 February 2008 - 04:42 PM.


#7 donjoe

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Posted 13 February 2008 - 11:18 PM

What's nagging me right now is that, having read this stuff about filter photo(in)stability, I went to look at the sunscreen I had left from last summer and found that it's got a methoxycinnamate and the benzophenone-3 (proven unstable filters) and none of the more "advanced" compounds that make other screens stable, so it's probably an unstable formulation. But seeing as it's still winter, I could use it without worrying too much if I knew which part of the spectrum actually causes the filters' photodegradation (i.e. if it turned out to be the UVBs, which are quite low at this time). From what I've read here, researchers always tried to use broad-spectrum lamps and never worried about which part of the radiation was destabilizing the filters, so I'm left to wonder: are unstable filters less risky or just as risky in winter as in summer?...

Edited by donjoe, 13 February 2008 - 11:20 PM.


#8 treonsverdery

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Posted 14 February 2008 - 02:22 AM

oral sunscreen complements dermal sunscreen
topical n oral use of ordinary Acetylsalicylic acid Ibuprofen naproxen known as Aleve are effective

Acetylsalicylic acid Ibuprofen naproxen known as Aleve

OralAll three drugs were effective in suppressing the UVB-, UVA- and combined UVA/UVB-erythema. However, the strongest effects were observed using the combined treatment with both 250 mg ASA and 10 mg mizolastine. An inhibitory effect in vitro of 10 nM mizolastine upon UV-induced cytokine release from HaCaT keratinocytes was observed for IL-1 alpha at 24 h after 10 J/cm2 UVA1, for IL-6 at 48 h after 10 J/cm2 UVA1 and 30 mJ/cm2 UVB, and also for TNF-alpha at 4 h after 10 J/cm2 UVA, 10 J/cm2 UVA1 and 30 mJ/cm2 UVB, respectively. The combination of mizolastine and ASA can be strongly recommended as a protective measure against UV erythema development with a lower unwanted side effect profile than that of the hitherto treatment modality, i.e. indomethacin.

Photoprotective effect of topical anti-inflammatory agents against ultraviolet radiation-induced chronic skin damage in the hairless mouse.Bissett DL, Chatterjee R, Hannon DP.
Procter & Gamble Company, Miami Valley Laboratories, Cincinnati, Ohio 45239-8707.

Albino hairless mice (Skh:HR-1) exposed chronically to suberythemal doses of ultraviolet (UV) radiation display visible and histological alterations in the skin. One alteration is an increase in dermal cellularity, including inflammatory cells. This suggested a role for inflammation in chronic photodamage. We evaluated the photoprotective effect of topical hydrocortisone, ibuprofen, and naproxen against photodamage. All 3 agents protected against UVB radiation-induced visible wrinkling, tumor formation, and histological alterations. Hydrocortisone and naproxen were also evaluated for protection against UVA radiation-induced visible skin sagging and histological alterations. Both were very effective. These data indicate that chronic topical application of anti-inflammatory agents provides broad solar UV spectrum photoprotection. http://www.ncbi.nlm....Pubmed_RVDocSum



Remodeling of the human dermis after application of salicylate silanol.Herreros FO, Cintra ML, Adam RL, de Moraes AM, Metze K.
Dermatology Unit, Department of Clinical Medicine, Faculty of Medicine, State University of Campinas, Campinas, Brazil.

Recently, a controlled double-blind study in patients with photo-aged facial skin demonstrated the beneficial role of oral intake of silanol for skin, hair and nails. The aim of our pilot study was to investigate histologic alterations in human skin after injection of silanol. Seven healthy female caucasian volunteers with a moderate degree of photoaged skin received ten sessions of weekly injections of 0.1% salicylate silanol in the left ventral lateral forearm. The histologic features of punch biopsies of the treated area and the nontreated contralateral arm were compared and the collagen and elastic fibers quantified. Texture analysis was performed on digitalized microscopic images by analyzing the Sarkar fractal dimension or amplitudes (inertia values) after Fast Fourier transformation. The treated area revealed a statistically significant increase of the density of both collagen and elastic fibers. Texture analysis showed more compact and homogeneously distributed collagen fibers after silicon injection. Our results suggest that the application of silicon may stimulate the production of collagen and elastic fibers leading to remodeling of the dermal fiber architecture, which may explain the improvement of the skin surface observed in clinical studies.



Anti-wrinkling effects of the mixture of vitamin C, vitamin E, pycnogenol and evening primrose oil, and molecular mechanisms on hairless mouse skin caused by chronic ultraviolet B irradiation.Cho HS, Lee MH, Lee JW, No KO, Park SK, Lee HS, Kang S, Cho WG, Park HJ, Oh KW, Hong JT.
LG Household & Healthcare Research Park, Daejeon, Korea.

BACKGROUND: Naturally occurring antioxidants were used to regulate the skin damage caused by ultraviolet (UV) radiation because several antioxidants have demonstrated that they can inhibit wrinkle formation through prevention of matrix metalloproteinases (MMPs) and/or increase of collagen synthesis. OBJECTIVE: We examined the effect of oral administration of the antioxidant mixture of vitamin C, vitamin E, pycnogenol, and evening primrose oil on UVB-induced wrinkle formation. In addition, we investigated the possible molecular mechanism of photoprotection against UVB through inhibition of collagen-degrading MMP activity or through enhancement of procollagen synthesis in mouse dorsal skin. METHODS: Female SKH-1 hairless mice were orally administrated the antioxidant mixture (test group) or vehicle (control group) for 10 weeks with UVB irradiation three times a week. The intensity of irradiation was gradually increased from 30 to 180 mJ/cm2. Microtopographic and histological assessment of the dorsal skins was carried out at the end of 10 weeks to evaluate wrinkle formation. Western blot analysis and EMSA were also carried out to investigate the changes in the balance of collagen synthesis and collagen degradation. RESULTS: Our antioxidant mixture significantly reduced UVB-induced wrinkle formation, accompanied by significant reduction of epidermal thickness, and UVB-induced hyperplasia, acanthosis, and hyperkeratosis. This antioxidant mixture significantly prevented the UVB-induced expressions of MMPs, mitogen-activated protein (MAP) kinase, and activation of activator protein (AP)-1 transcriptional factor in addition to enhanced type I procollagen and transforming growth factor-beta2 (TGF-beta2) expression. CONCLUSION: Oral administration of the antioxidant mixture significantly inhibited wrinkle formation caused by chronic UVB irradiation through significant inhibition of UVB-induced MMP activity accompanied by enhancement of collagen synthesis.



http://www.ncbi.nlm....Pubmed_RVDocSum

note the peculiar UVA UVB thing

Evaluation of the photostability of different UV filter combinations in a sunscreen
.Gaspar LR, Maia Campos PM.
Universidade de São Paulo, Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Bairro Monte Alegre, Ribeirão Preto, SP, Brazil.

Development of photostable sunscreens is extremely important to preserve the UV protective capacity and to prevent the reactive intermediates of photounstable filter substances behaving as photo-oxidants when coming into direct contact with the skin. Thus, the objective of this study was to evaluate the photostability of four different UV filter combinations in a sunscreen by using HPLC analysis and spectrophotometry. The formulations that were investigated included four different UV filter combinations often used in SPF 15 sunscreens. The UV filter combinations were: octyl methoxycinnamate (OMC), benzophenone-3 (BP-3) and octyl salicylate (OS) (formulation 1); OMC, avobenzone (AVB) and 4-methylbenzilidene camphor (MBC) (formulation 2); OMC, BP-3 and octocrylene (OC) (formulation 3); OMC, AVB and OC (formulation 4). In the photostability studies, 40 mg of each formulation were spread onto a glass plate and left to dry before exposure to different UVA/UVB irradiation. Exposed samples were then immersed in isopropanol and the dried film dissolved ultrasonically. The filter components in the resulting solution were quantified by HPLC analysis with detection at 325 nm and by spectrophotometry. In this study, the four UV filter combinations showed different photostability profiles and the best one was formulation 3 (OMC, BP-3 and OC), followed by formulations 4, 1 and 2. In addition, OC improved the photostability of OMC, AVB and BP-3.

Edited by treonsverdery, 14 February 2008 - 02:41 AM.


#9 donjoe

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Posted 14 February 2008 - 06:20 AM

the best one was formulation 3 (OMC, BP-3 and OC)

Well whadda ya know. Looking at the other attachments here, I was already starting to suspect that maybe in the 2006 study I (re)quoted they used some unrealistic formulations where OC, OMC and BP-3 weren't associated with anything else, but used in complete separation, and that's why they proved unstable. This 2007 study here suggests that's the case, because the same filters combined created a stable product.

#10 Eva Victoria

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Posted 14 February 2008 - 06:00 PM

oral sunscreen complements dermal sunscreen
topical n oral use of ordinary Acetylsalicylic acid Ibuprofen naproxen known as Aleve are effective

Acetylsalicylic acid Ibuprofen naproxen known as Aleve

OralAll three drugs were effective in suppressing the UVB-, UVA- and combined UVA/UVB-erythema. However, the strongest effects were observed using the combined treatment with both 250 mg ASA and 10 mg mizolastine. An inhibitory effect in vitro of 10 nM mizolastine upon UV-induced cytokine release from HaCaT keratinocytes was observed for IL-1 alpha at 24 h after 10 J/cm2 UVA1, for IL-6 at 48 h after 10 J/cm2 UVA1 and 30 mJ/cm2 UVB, and also for TNF-alpha at 4 h after 10 J/cm2 UVA, 10 J/cm2 UVA1 and 30 mJ/cm2 UVB, respectively. The combination of mizolastine and ASA can be strongly recommended as a protective measure against UV erythema development with a lower unwanted side effect profile than that of the hitherto treatment modality, i.e. indomethacin.

Photoprotective effect of topical anti-inflammatory agents against ultraviolet radiation-induced chronic skin damage in the hairless mouse.Bissett DL, Chatterjee R, Hannon DP.
Procter & Gamble Company, Miami Valley Laboratories, Cincinnati, Ohio 45239-8707.

Albino hairless mice (Skh:HR-1) exposed chronically to suberythemal doses of ultraviolet (UV) radiation display visible and histological alterations in the skin. One alteration is an increase in dermal cellularity, including inflammatory cells. This suggested a role for inflammation in chronic photodamage. We evaluated the photoprotective effect of topical hydrocortisone, ibuprofen, and naproxen against photodamage. All 3 agents protected against UVB radiation-induced visible wrinkling, tumor formation, and histological alterations. Hydrocortisone and naproxen were also evaluated for protection against UVA radiation-induced visible skin sagging and histological alterations. Both were very effective. These data indicate that chronic topical application of anti-inflammatory agents provides broad solar UV spectrum photoprotection. http://www.ncbi.nlm....Pubmed_RVDocSum



Remodeling of the human dermis after application of salicylate silanol.Herreros FO, Cintra ML, Adam RL, de Moraes AM, Metze K.
Dermatology Unit, Department of Clinical Medicine, Faculty of Medicine, State University of Campinas, Campinas, Brazil.

Recently, a controlled double-blind study in patients with photo-aged facial skin demonstrated the beneficial role of oral intake of silanol for skin, hair and nails. The aim of our pilot study was to investigate histologic alterations in human skin after injection of silanol. Seven healthy female caucasian volunteers with a moderate degree of photoaged skin received ten sessions of weekly injections of 0.1% salicylate silanol in the left ventral lateral forearm. The histologic features of punch biopsies of the treated area and the nontreated contralateral arm were compared and the collagen and elastic fibers quantified. Texture analysis was performed on digitalized microscopic images by analyzing the Sarkar fractal dimension or amplitudes (inertia values) after Fast Fourier transformation. The treated area revealed a statistically significant increase of the density of both collagen and elastic fibers. Texture analysis showed more compact and homogeneously distributed collagen fibers after silicon injection. Our results suggest that the application of silicon may stimulate the production of collagen and elastic fibers leading to remodeling of the dermal fiber architecture, which may explain the improvement of the skin surface observed in clinical studies.



Anti-wrinkling effects of the mixture of vitamin C, vitamin E, pycnogenol and evening primrose oil, and molecular mechanisms on hairless mouse skin caused by chronic ultraviolet B irradiation.Cho HS, Lee MH, Lee JW, No KO, Park SK, Lee HS, Kang S, Cho WG, Park HJ, Oh KW, Hong JT.
LG Household & Healthcare Research Park, Daejeon, Korea.

BACKGROUND: Naturally occurring antioxidants were used to regulate the skin damage caused by ultraviolet (UV) radiation because several antioxidants have demonstrated that they can inhibit wrinkle formation through prevention of matrix metalloproteinases (MMPs) and/or increase of collagen synthesis. OBJECTIVE: We examined the effect of oral administration of the antioxidant mixture of vitamin C, vitamin E, pycnogenol, and evening primrose oil on UVB-induced wrinkle formation. In addition, we investigated the possible molecular mechanism of photoprotection against UVB through inhibition of collagen-degrading MMP activity or through enhancement of procollagen synthesis in mouse dorsal skin. METHODS: Female SKH-1 hairless mice were orally administrated the antioxidant mixture (test group) or vehicle (control group) for 10 weeks with UVB irradiation three times a week. The intensity of irradiation was gradually increased from 30 to 180 mJ/cm2. Microtopographic and histological assessment of the dorsal skins was carried out at the end of 10 weeks to evaluate wrinkle formation. Western blot analysis and EMSA were also carried out to investigate the changes in the balance of collagen synthesis and collagen degradation. RESULTS: Our antioxidant mixture significantly reduced UVB-induced wrinkle formation, accompanied by significant reduction of epidermal thickness, and UVB-induced hyperplasia, acanthosis, and hyperkeratosis. This antioxidant mixture significantly prevented the UVB-induced expressions of MMPs, mitogen-activated protein (MAP) kinase, and activation of activator protein (AP)-1 transcriptional factor in addition to enhanced type I procollagen and transforming growth factor-beta2 (TGF-beta2) expression. CONCLUSION: Oral administration of the antioxidant mixture significantly inhibited wrinkle formation caused by chronic UVB irradiation through significant inhibition of UVB-induced MMP activity accompanied by enhancement of collagen synthesis.



http://www.ncbi.nlm....Pubmed_RVDocSum

note the peculiar UVA UVB thing

Evaluation of the photostability of different UV filter combinations in a sunscreen
.Gaspar LR, Maia Campos PM.
Universidade de São Paulo, Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Bairro Monte Alegre, Ribeirão Preto, SP, Brazil.

Development of photostable sunscreens is extremely important to preserve the UV protective capacity and to prevent the reactive intermediates of photounstable filter substances behaving as photo-oxidants when coming into direct contact with the skin. Thus, the objective of this study was to evaluate the photostability of four different UV filter combinations in a sunscreen by using HPLC analysis and spectrophotometry. The formulations that were investigated included four different UV filter combinations often used in SPF 15 sunscreens. The UV filter combinations were: octyl methoxycinnamate (OMC), benzophenone-3 (BP-3) and octyl salicylate (OS) (formulation 1); OMC, avobenzone (AVB) and 4-methylbenzilidene camphor (MBC) (formulation 2); OMC, BP-3 and octocrylene (OC) (formulation 3); OMC, AVB and OC (formulation 4). In the photostability studies, 40 mg of each formulation were spread onto a glass plate and left to dry before exposure to different UVA/UVB irradiation. Exposed samples were then immersed in isopropanol and the dried film dissolved ultrasonically. The filter components in the resulting solution were quantified by HPLC analysis with detection at 325 nm and by spectrophotometry. In this study, the four UV filter combinations showed different photostability profiles and the best one was formulation 3 (OMC, BP-3 and OC), followed by formulations 4, 1 and 2. In addition, OC improved the photostability of OMC, AVB and BP-3.


Hydrocortisone actually makes skin photosensitive when applied topically!

#11 niner

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Posted 15 February 2008 - 05:20 AM

Eva (or anyone who knows), if I'm spending most of my time indoors on in a car, with only short trips from car to buildings as my full sun exposure, and I'm not bathing or sweating, it would seem to me that I could get by with a much longer interval between applications of sunscreen. I'm hoping for all day, to be honest. Is this reasonable, or will a sunscreen deteriorate even without a lot of UV exposure?

#12 donjoe

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Posted 15 February 2008 - 07:10 AM

Eva (or anyone who knows), if I'm spending most of my time indoors on in a car, with only short trips from car to buildings as my full sun exposure, and I'm not bathing or sweating, it would seem to me that I could get by with a much longer interval between applications of sunscreen. I'm hoping for all day, to be honest. Is this reasonable, or will a sunscreen deteriorate even without a lot of UV exposure?

That's what I was hoping too. I have similar daily exposure (no more than one hour outside, total), so I'm thinking the main problem is continuous (but not constant) UVA exposure, especially if the blinds on the windows aren't drawn and I'm sitting pretty close to it (but that varies). If there were any sunscreen photostability experiments where they hadn't just used one broad-spectrum lamp, but tried a selection of different narrow-band ones, we'd be in a better position to say whether you actually have to go outside to ruin your sunscreen (by UVB) or if it can happen just as easily inside the house, behind uncovered glass windows (by UVA).

#13 Eva Victoria

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Posted 15 February 2008 - 01:29 PM

If you read my attachments carefully you'll notice that it says that sunscreens are also absorbed by the skin and when they are migrated to deeper layers of the skin (approx. after 2h) then they not only not protect against UV-rays but also scatter light within your own skin. Meaning they damage the skin more since they scatter light within the skin).
It of course applies to chemical sunscreens. Physical sunscreens (TiO2, ZnO) they have too big molecules to be able to cross the epidermal skin cells on the surfaceof the skin and enter into deeper layers.

So you should reapply sunscreen EVERY 2 HOURS.

#14 donjoe

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Posted 15 February 2008 - 04:16 PM

If you read my attachments carefully you'll notice that it says that sunscreens are also absorbed by the skin and when they are migrated to deeper layers of the skin (approx. after 2h) then they [...] scatter light within your own skin. Meaning they damage the skin more since they scatter light within the skin).

1. False. None of your attachments say any such thing. (I just checked them all.) Scattering is always mentioned as a positive effect of inorganic filters, so I'm assuming they mean reflective scattering (keeping the radiation away from the skin) rather than transmissive scattering (letting the radiation through into the skin).
2. Assuming small inorganic particles got inside the skin and assuming they still had a scattering effect in there, it's hard to see why this would cause more damage, seeing as it couldn't possibly increase the total energy radiated into the skin. When rays are scattered, their total energy is the same, their frequency is the same, only their direction changes. I don't see anything particularly destructive about that (once we've admitted that the radiation has already "broken into" the skin).

#15 Eva Victoria

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Posted 15 February 2008 - 08:24 PM

If you read my attachments carefully you'll notice that it says that sunscreens are also absorbed by the skin and when they are migrated to deeper layers of the skin (approx. after 2h) then they [...] scatter light within your own skin. Meaning they damage the skin more since they scatter light within the skin).

1. False. None of your attachments say any such thing. (I just checked them all.) Scattering is always mentioned as a positive effect of inorganic filters, so I'm assuming they mean reflective scattering (keeping the radiation away from the skin) rather than transmissive scattering (letting the radiation through into the skin).
2. Assuming small inorganic particles got inside the skin and assuming they still had a scattering effect in there, it's hard to see why this would cause more damage, seeing as it couldn't possibly increase the total energy radiated into the skin. When rays are scattered, their total energy is the same, their frequency is the same, only their direction changes. I don't see anything particularly destructive about that (once we've admitted that the radiation has already "broken into" the skin).


I`ll find the proper study where it says what I wrote in my prev. post. So long have a look at this:

"But over time, the filters themselves penetrate deeper into the skin, allowing more UV radiation in."
http://www.livescien...en_problem.html

Edited by Eva Victoria, 15 February 2008 - 08:36 PM.


#16 niner

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Posted 16 February 2008 - 04:53 AM

"But over time, the filters themselves penetrate deeper into the skin, allowing more UV radiation in."
http://www.livescien...en_problem.html

Most sunscreen makers say that you should apply the sunscreen some amount of time before you go out in the sun. This suggests that they want it to be absorbed at least into the top layer of the skin. So some absorption is good, I guess, and too much absorption is... too much. Now, lets assume that it's really true that the filters, once absorbed, will create ROS. If there were no filters at all, the UV photons would still penetrate the deeper layers of skin. What's not clear to me is that the UV photons would do less damage without the filters than with them. Are there mechanisms for photons in the UVA range to get absorbed without doing damage? I haven't read Hanson's paper; does he present any evidence that deeply absorbed filters are worse than no filters at all?

#17 donjoe

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Posted 16 February 2008 - 06:08 AM

What's not clear to me is that the UV photons would do less damage without the filters than with them. Are there mechanisms for photons in the UVA range to get absorbed without doing damage? I haven't read Hanson's paper; does he present any evidence that deeply absorbed filters are worse than no filters at all?

Again, yes - but only photounstable filters, nota bene. And going beyond my earlier abstract-only quote, this is from Eva's first attachment:

According to the free radical theory of photoaging of human skin generation of ROS results in the formation of protein cross-links in collagen and certain enzymes such as catalase and superoxide dismutase (Dalle Carbonare and Pathak, 1992). These authors showed that protein inactivation was more significant by UVA irradiation in the presence of sensitizers than by UVA without sensitizers. There is increasing evidence that oxidative stress is involved in skin carcinogenesis. ROS seem to be responsible for the induction of 8-hydroxy-2'-deguanosin in arsenic-related nonmelanoma skin cancer (Matsui et al, 1999). The presence of 8-hydroxy-2'-deguanosin-mediated DNA defects in UV-induced skin cancers in mice (Nishigori et al, 1994) indicated ROS as cofactors of photocarcinogenesis. This seems to be the mechanism for the significantly higher number of strandbreaks of singlestranded DNA by UV irradiation in the presence of octyl dimethyl PABA (padimate-O) when compared with UV irradiation alone (McHugh and Knowland, 1997). In basal keratinocytes padimate-O significantly increased indirect DNA damage (strand breaks) when exposed to UV radiation even though the sunscreen film reduced direct UV damage (Gulston and Knowland, 1999). This indirect (ROS-mediated) DNA damage could be suppressed completely by oxygen quenchers. The study by Gulston and Knowland (1999), therefore, strongly supports the model of a dual mechanism of UVA-induced skin damage. Surprisingly, padimate-O, which penetrates the skin (Kenney et al, 1995), is still advertised as a chemically inert, safe, and photostable UVB filter (Klein, 1997). Photoinstability of UV filters may be responsible for the
high frequency of photosensitive reactions induced by sunscreens. The hypothesis that reactive photolysis products may behave as haptens or induce toxic cell damage (Chignell et al, 1980) is supported by the results of three recent studies presenting the patch and photopatch test results in persons with suspected photosensitivity to sunscreen ingredients (Szcurko et al, 1994; Schauder and Ippen, 1997; Journe et al, 1999). In their review of 402 patients Schauder and Ippen (1997) found that UVA filters were responsible for the majority of positive photopatch test results (54 reactions) when compared with UVB filters (30 reactions). The photounstable absorbers isopropyldibenzoylmethane and butyl methoxydibenzoylmethane gave 32 and 13 positive reactions, respectively. Photostable terephthalylidene dicamphor sulfonic acid, however, showed no positive reactions in this follow-up. The most important photosensitizers in the survey by Szczurko et al (1994) were oxybenzone, octyl dimethyl PABA and isopropyldibenzoylmethane and in the follow-up by Journe et al (1999) oxybenzone and isopropyl dibenzoylmethane.

(I'm not sure what they mean by "oxygen quenchers". Maybe antioxidants. *shrugs*)

However, given the other conclusions drawn by the same study - that the same filter combined with different others gives different stability results, and even the same overall combination of filters can be stable or unstable depending on the cream phase/base - these conclusions about particular filters should be taken with a grain of salt (at least until one can review the referenced studies to see exactly what products were tested).


ETA:
I think I've found a good source of data on filter photostability in combinations:
http://skindeep.ewg....s...&nothanks=1

The above link is for oxybenzone/benzophenone-3. If you scroll down, you'll notice that it's unstable in most combinations (as already shown by the references in this thread), but there is one combination wherein it can be stabilised: if it's mixed with homosalate and octylmethoxycinnamate. (Indeed, we saw an earlier quote where it was combined with OMC and octocrylene and the sunscreen proved stable, so there must be something to the BP-3 + OMC pair that keeps them stable even when mixed with other things. Incidentally, my current sunscreen has this pair in it and although there's no octocrylene or homosalate, it does say "photostable" on the bottle. I now have strong reason to believe it. ;))

I can't seem to find a way to get a detailed page like the one at the link above for other filters. If I use the search form provided by the site, I get a different (albeit still useful) "ingredient page". If no-one finds out how, here's a "dirty" way to do it:
- use the search form to find the "ingredient page" of the filter you want to research;
- look at the updated URL of that page in your browser's address bar - it should end with "ingred06=" followed by a number;
- edit the URL: replace "ingredient.php" with "special/sunscreens/actives/index.php" and hit Enter.
Now you should see the detailed page for that filter, where it says which combinations it's been shown to be (un)stable in, with scientific references.

Edited by donjoe, 16 February 2008 - 07:09 AM.


#18 Eva Victoria

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Posted 16 February 2008 - 02:10 PM

"But over time, the filters themselves penetrate deeper into the skin, allowing more UV radiation in."
http://www.livescien...en_problem.html

Most sunscreen makers say that you should apply the sunscreen some amount of time before you go out in the sun. This suggests that they want it to be absorbed at least into the top layer of the skin. So some absorption is good, I guess, and too much absorption is... too much. Now, lets assume that it's really true that the filters, once absorbed, will create ROS. If there were no filters at all, the UV photons would still penetrate the deeper layers of skin. What's not clear to me is that the UV photons would do less damage without the filters than with them. Are there mechanisms for photons in the UVA range to get absorbed without doing damage? I haven't read Hanson's paper; does he present any evidence that deeply absorbed filters are worse than no filters at all?


He does not. But studies have shown that if you don't reapply your sunscreen every 2 h than ROS formation is greater than that of unprotected skin. :( Hence you should reapply your sunscreen every 2 h.
And yes, you should apply sunscrees 20 min BEFORE sunexposure as well (this is partly for having time to cover the entire area where sunscreen is put).

Og course all this applies for chemical sunscreens.

#19 Eva Victoria

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Posted 16 February 2008 - 02:21 PM

What's not clear to me is that the UV photons would do less damage without the filters than with them. Are there mechanisms for photons in the UVA range to get absorbed without doing damage? I haven't read Hanson's paper; does he present any evidence that deeply absorbed filters are worse than no filters at all?

Again, yes - but only photounstable filters, nota bene. And going beyond my earlier abstract-only quote, this is from Eva's first attachment:

According to the free radical theory of photoaging of human skin generation of ROS results in the formation of protein cross-links in collagen and certain enzymes such as catalase and superoxide dismutase (Dalle Carbonare and Pathak, 1992). These authors showed that protein inactivation was more significant by UVA irradiation in the presence of sensitizers than by UVA without sensitizers. There is increasing evidence that oxidative stress is involved in skin carcinogenesis. ROS seem to be responsible for the induction of 8-hydroxy-2'-deguanosin in arsenic-related nonmelanoma skin cancer (Matsui et al, 1999). The presence of 8-hydroxy-2'-deguanosin-mediated DNA defects in UV-induced skin cancers in mice (Nishigori et al, 1994) indicated ROS as cofactors of photocarcinogenesis. This seems to be the mechanism for the significantly higher number of strandbreaks of singlestranded DNA by UV irradiation in the presence of octyl dimethyl PABA (padimate-O) when compared with UV irradiation alone (McHugh and Knowland, 1997). In basal keratinocytes padimate-O significantly increased indirect DNA damage (strand breaks) when exposed to UV radiation even though the sunscreen film reduced direct UV damage (Gulston and Knowland, 1999). This indirect (ROS-mediated) DNA damage could be suppressed completely by oxygen quenchers. The study by Gulston and Knowland (1999), therefore, strongly supports the model of a dual mechanism of UVA-induced skin damage. Surprisingly, padimate-O, which penetrates the skin (Kenney et al, 1995), is still advertised as a chemically inert, safe, and photostable UVB filter (Klein, 1997). Photoinstability of UV filters may be responsible for the
high frequency of photosensitive reactions induced by sunscreens. The hypothesis that reactive photolysis products may behave as haptens or induce toxic cell damage (Chignell et al, 1980) is supported by the results of three recent studies presenting the patch and photopatch test results in persons with suspected photosensitivity to sunscreen ingredients (Szcurko et al, 1994; Schauder and Ippen, 1997; Journe et al, 1999). In their review of 402 patients Schauder and Ippen (1997) found that UVA filters were responsible for the majority of positive photopatch test results (54 reactions) when compared with UVB filters (30 reactions). The photounstable absorbers isopropyldibenzoylmethane and butyl methoxydibenzoylmethane gave 32 and 13 positive reactions, respectively. Photostable terephthalylidene dicamphor sulfonic acid, however, showed no positive reactions in this follow-up. The most important photosensitizers in the survey by Szczurko et al (1994) were oxybenzone, octyl dimethyl PABA and isopropyldibenzoylmethane and in the follow-up by Journe et al (1999) oxybenzone and isopropyl dibenzoylmethane.

(I'm not sure what they mean by "oxygen quenchers". Maybe antioxidants. *shrugs*)

However, given the other conclusions drawn by the same study - that the same filter combined with different others gives different stability results, and even the same overall combination of filters can be stable or unstable depending on the cream phase/base - these conclusions about particular filters should be taken with a grain of salt (at least until one can review the referenced studies to see exactly what products were tested).


ETA:
I think I've found a good source of data on filter photostability in combinations:
http://skindeep.ewg....s...&nothanks=1

The above link is for oxybenzone/benzophenone-3. If you scroll down, you'll notice that it's unstable in most combinations (as already shown by the references in this thread), but there is one combination wherein it can be stabilised: if it's mixed with homosalate and octylmethoxycinnamate. (Indeed, we saw an earlier quote where it was combined with OMC and octocrylene and the sunscreen proved stable, so there must be something to the BP-3 + OMC pair that keeps them stable even when mixed with other things. Incidentally, my current sunscreen has this pair in it and although there's no octocrylene or homosalate, it does say "photostable" on the bottle. I now have strong reason to believe it. ;) )

I can't seem to find a way to get a detailed page like the one at the link above for other filters. If I use the search form provided by the site, I get a different (albeit still useful) "ingredient page". If no-one finds out how, here's a "dirty" way to do it:
- use the search form to find the "ingredient page" of the filter you want to research;
- look at the updated URL of that page in your browser's address bar - it should end with "ingred06=" followed by a number;
- edit the URL: replace "ingredient.php" with "special/sunscreens/actives/index.php" and hit Enter.
Now you should see the detailed page for that filter, where it says which combinations it's been shown to be (un)stable in, with scientific references.


At Skin Deep (your link) it says OMC+BP3 is an unstable pair.
I have tested this combo several time in the lab. and it is not only photo-unstable but it does not provide adequate UVA protection!
It is very common in American sunscreens to use this combo (+ZnO) but it is not a good combo nevertheless.
If you live in Europe, you can access much better filters than this combo.
Again I'd like to point out the perfection (today's standard) of the Mexoryl filters and the Tinosorb family. They are both photostable and provide good UVA protection.

BTW, Skin Deep is an American site, you won't find any sunscreens there that contain Mexoryl XL and Tinosorb M+S (since none of these filters are available in the US; only Mexoryl SX).

#20 donjoe

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Posted 16 February 2008 - 11:51 PM

At Skin Deep (your link) it says OMC+BP3 is an unstable pair.

Oh. Right. I hadn't looked at the isolated pair. Thanx for the heads-up! ;)

I have tested this combo several time in the lab. and it is not only photo-unstable but it does not provide adequate UVA protection!

Noted. Of course, I wasn't planning on long-term usage, because I simply don't like the idea of "purely-chemical" protection. I do want to get something else as soon as I find the oportunity.

BTW, Skin Deep is an American site, you won't find any sunscreens there that contain Mexoryl XL and Tinosorb M+S (since none of these filters are available in the US; only Mexoryl SX).

Well, OK, but it's still useful if you want centralised information about the stability of filter combinations that don't contain these particular substances. Do you know a better similar resource?

#21 Eva Victoria

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Posted 17 February 2008 - 09:50 AM

At Skin Deep (your link) it says OMC+BP3 is an unstable pair.

Oh. Right. I hadn't looked at the isolated pair. Thanx for the heads-up! ;)

I have tested this combo several time in the lab. and it is not only photo-unstable but it does not provide adequate UVA protection!

Noted. Of course, I wasn't planning on long-term usage, because I simply don't like the idea of "purely-chemical" protection. I do want to get something else as soon as I find the oportunity.

BTW, Skin Deep is an American site, you won't find any sunscreens there that contain Mexoryl XL and Tinosorb M+S (since none of these filters are available in the US; only Mexoryl SX).

Well, OK, but it's still useful if you want centralised information about the stability of filter combinations that don't contain these particular substances. Do you know a better similar resource?


Nope :( Only the site of the manufacturers and dermatological journals :(
The down side with Skin Deep is that it does not take it into account that some UV-filters (permitted in EU, not US) can actually make both OMC+BP3 photostable. So when you read the ingredients lable on the sunscreen tube and you`ll see OMC & BP3 you`ll think that that sunscreen is not photostable, when it might as well contain other ingr. that stabilize these to chemical filters.
This is the reason I always refer to Mexoryl SX+XL and Tinosorb M+S because we have tested them numerous times in the lab with different UV length and they not only protect very well in the UVA 2-1 range but also photostable.

I however use a good old blend of TiO2 (12%) ZnO (10%) in silicone oil. TiO2 is micronized but ZnO is >200nm. It is whitening but gives full protection in both UVB and UVA2-1 range. (SPF50, PPD measured at 360nm 15; at 400nm 10; meaning PPD15 is 93% filtering of UVA rays; PPD 10 is 90%).

#22 donjoe

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Posted 17 February 2008 - 02:53 PM

The down side with Skin Deep is that it does not take it into account that some UV-filters (permitted in EU, not US) can actually make both OMC+BP3 photostable.

They don't have to. The conclusions listed there are for the exact combinations mentioned; nothing should be assumed about any "similar" combinations where something is added or removed. It takes an informed reader to use that site and understand the limits of the information provided. ;)

#23 Eva Victoria

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Posted 17 February 2008 - 06:45 PM

The down side with Skin Deep is that it does not take it into account that some UV-filters (permitted in EU, not US) can actually make both OMC+BP3 photostable.

They don't have to. The conclusions listed there are for the exact combinations mentioned; nothing should be assumed about any "similar" combinations where something is added or removed. It takes an informed reader to use that site and understand the limits of the information provided. ;)



Read my previous post again and try to understand it. You can do it! ;)

Edited by Eva Victoria, 17 February 2008 - 06:51 PM.


#24 donjoe

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Posted 18 February 2008 - 06:30 PM

Read my previous post again and try to understand it. You can do it! ;)

Err... yeah. :| You didn't understand what I said and I didn't understand what you said. Let's leave it at that.

#25 Eva Victoria

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Posted 19 February 2008 - 08:21 AM

Agree.

Read my previous post again and try to understand it. You can do it! :~

Err... yeah. :| You didn't understand what I said and I didn't understand what you said. Let's leave it at that.



#26 treonsverdery

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Posted 19 February 2008 - 08:48 AM

humor value:

knock knock Why reapply your sunscreen every 2h?
whos there
because relativistic acceleration can turn any wavelength of photons to UV; as well as stretch your physiological observer time relative to an observer

thus, there is always a frame of reference where this advice has value


localization hint: the "knock knock joke" format is generally well known among English speaking North Americans

actual idea

I think the geometry of things like TiO2 particles matters a bunch; its possible flat <=> shapes or even TiO2 plated onto conductive polymer flat shapes would act as charge carriers; basically the electron potential of the multiple free radicals accumulates on the conductive polymer creating an cumulative electric charge that is less reactive to the UVA absorbing chemicals

I know i didn't make sense there but basically TiO2 is also a photovoltaic chemical; microstructured photovoltaics like TiO2 but different might turn UV to electric charge that was neutral to sunscreen ngredients

Edited by treonsverdery, 19 February 2008 - 09:10 AM.


#27 tao81

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Posted 26 March 2008 - 03:17 PM

So if i understood right only creams with chemical photounstable filters have to be aplyed every 2 h.
If I use a good photostable cream than this ROS problem shouldn´t occur and you dont need to reapply them all the time.
Like Mexoryl filters or physical like ZnO??
To be honest i don´t want to reapply my cream every 2 h!I want to put it on in the morning and that´s it...(At the beach I reapply it for sure but at home...)
One thing more: is this a good photostable sunsreen?
thx alot


Aqua
Alcohol Denat.
Butylene Glycol
Tocopherol
Tocopheryl Acetate
Glycerin
Vitis Vinifera Seed Extract
Ascorbyl Tetraisopalmitat
Ubiquinone
Diisopropyl Adipate
Acrylates/C10-30 Alkyl Acrylate
Hydroxyethylcellulose
Disodium EDTA

INCI-Namen des Filtersystems
Isoamyl p-Methoxycinnamate
Ethylhexyl Methoxycinnamate
Ethylhexyl Triazone
Butyl Methoxydibenzoylmethane



Edited by tao81, 26 March 2008 - 03:18 PM.


#28 donjoe

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Posted 26 March 2008 - 08:49 PM

is this a good photostable sunsreen?

IMHO, you shouldn't bet any large sum of money on it. :-D Ethylhexyl triazone... OMC+AVO... nothing you have there sounds stable to me (from what little I've read so far). Maybe Eva can quote you some concrete result about that exact combination, but if it were me I'd forget this one and keep looking.




- After all, Number One, we're only mortal.
- Speak for yourself, sir. I plan to live forever.

Edited by donjoe, 26 March 2008 - 08:50 PM.


#29 sdxl

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Posted 27 March 2008 - 12:41 AM

Ethylhexyl triazone is one of the best UVB absorbers. It's highly photostable. The cinnamates are not and the combination with avobenzone makes it worse for both. I wouldn't use that sunscreen.

#30 tao81

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Posted 27 March 2008 - 12:45 PM

Wow thx this creme ought to be a good one...
I will opt for an other creme-!maybe you can give a vote for the new one too.
But in regard to the other question-occurs this problem with increased ROS only to photounstable filters or to every chemical filters if you don´t reapply it??-that would be very bad!
If that was true I think I would have to change to physical filters -but c these filters make your face white thats bad too...
I´m really confused about it.I appreciate every comment.
thx




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