I wonder to what extent, if any, topical vitamin d has any benefits for the skin. Vitamin D seems to benefit so many organs, so why not the skin? It's dirt cheap and it is absorbed by the skin very well. ( I bit open a capsule and applied it).
When I googled vitamin D and skin, about the only relevance I found was Vitamin D's ability to promote cathelicidin in the skin, which the immune system uses to fight infections. I would bet that topical vitamin d would be very good for eczema. And I have a hunch that topical vitamin D would have skin benefits beyond fighting off infection, but nothing to back that up.