Why does a sunburn peel?

A sunburn is a first degree burn. As painful as being scalded with hot water and just as damaging to the flesh killing the cells of several layers of skin cells. When skin cells die they dry and flake off and we usually never even notice. 90% of the dust in a home is comprised of dead skin cells of the occupants. Dandruff is also nothing more than dead skin cells. When you get a sunburn, the body stops supplying those cells with nutrients. The tender flesh beneath is still in close proximity to blood capillaries and nerve tissues. Standard secretion of sweat and skin oils help to push away and shed the damaged and dead skin cells when it is ready. That is what causes the peeling. It's usually better to let the skin peel naturally, so the tender flesh beneath isn't exposed until it is ready.