Re: What chemical changes actually occur in the skin to obtain a sunburn(tan)?

Dear Bobby,

Skin burns or tans as a response to damaging effects of ultraviolet (UV) light. The cell biology of this process has been summarized in a scientific article in the journal "Developmental Biology" (vol. 183, p. 123-138, 1997, an article by F. Bernerd and D. Asselineau).

The authors of this article note that UV light damages DNA in epidermal skin cells. All cells contain enzymes that detect damaged DNA. Damaged DNA can sometimes be repaired; if, however, the damage is too great, mechanisms for cell death, called apoptosis, are activated that kill the cell and prevent its mutated DNA from causing harm, as in cancers, etc.

Dying skin cells are called "sunburn cells." These dying cells can release chemicals (eg., one is called tumor necrosis factor) that can cause other neighboring cells to also die. Eventually, dying cells flake off the burned skin and are replaced. Another cell type called a melanocyte speeds up the synthesis of a dark pigment called melanin. The melanin is transferred from melanocytes to the rest of the skin cells, where it absorbs harmful UV light and prevents any more damage to DNA. This is what causes a suntan. It's unclear how the melanocytes "know" when it is time to make more melanin. Perhaps they respond to chemical signals from other damaged cells. Alternatively, it is known that melanin making cells of some animals (eg., frogs) have their own form of visual pigment similar to that in the retina (see "Melanopsin: an opsin in melanophores, brain, and eye" in Proceedings of the National Academy of Sciences, vol. 95, p. 340, 1998 by I. Provencio--you can look up this article online by going to www.ncbi.nlm.nih.gov). Perhaps melanocytes "sense" sunlight directly.