This is part 3 of our multi-part series on Human Skin Color.

Suntanning is a fascinating process. UV radiation from the sun stimulates pigment producing skin cells to increase the amount of the dark pigment eumelanin that is produced. This can be stimulated in a number of ways; here, we focus on two mechanisms that deal with (1) an increase in the production of the tyrosinase enzyme and (2) the re-activation of the tyrosinase enzyme after it is deactivated, as part of its use in the eumelanin biosynthetic production pathway. It is worth noting though that the phenomenon of skin-tanning is not ubiquitous across the human species. People who already have high levels of eumelanin in their skin may not be able to produce (much) more pigment, because they are already at eumelanin saturation. Conversely, some humans with very very low levels of eumelanin may be biologically unable to tan due to mutations in their MC1R gene (as one example).

For more information on the biology of human skin color, visit www.evo-ed.org.

Support for this work was provided by the National Science Foundation's Division of Undergraduate Education program under Award No. DUE2020221