I have a Book that was written in 1950 that cost $50, the author was a health advisor to movie stars. He and his wife were cubans. They would spend many months in the states and then return to cuba the author said he and his wife would lay naked in the sand and allow all their diseased skin to peel off. He said the foods they ate in the states was harmful and once out of their sytems and all the bad skin expelled, then their skin and health returned to them. The one thing I remember about their book was they advocated living outside, in that your home had open exposed walls.
The skin expels much of the human waste, aka foods, so in theory, our skin is sick and very well could be the reason for some degree of the sun burn.