The top layers of skin, aka ‘the horny layer’ are all dead skin cells and have no effect on Vitamin D production. Vitamin D is converted lower in the live skin cells.
This thought may have started when Coppertone and other tanning lotions included ‘self tanner’ ingredients in the formulation. They require 3-4 hours to activate in the skin, hence the ‘Don’t shower right after sun exposure’ may have started.
Hope this helps
Answered by tanlines on December 18, 2014 at 9:15 am