The retinoid receptors in the skin (face) can be disabled by UVA sun radiation as these study states : https://www.sciencedaily.com/releases/1999/03/990331063314.htm
In this article it says the same : http://www.abc.net.au/news/science/2015-11-18/how-uv-light-damages-our-skin/6856742
" UVA activates receptors that produce the enemy of firm skin: matrix metalloproteinases. These enzymes have one job and they do it beautifully: breaking down collagen. And it doesn’t take much UV at all to get this going, so even without sunburn any parts of your skin that are exposed to the sun will age.
As if the collagen attack wasn't insult enough, UV radiation also interferes with the production of Vitamin A receptors on our skin cells.
Vitamin A is critical for cell growth in our skin, but without functioning receptors for the vitamin to activate, our skin ends up thinning, and that’s something no amount of carrots can fix.
Question is: do these receptors actually work again after sun exposure is stopped? Or any topical/oral treatment with vitamin a will be useless for skin regeneration?