The Function of Melanin

To the Editor.—  Warwick L. Morison, MD, in the September 1985 issue of the Archives¹ ably questions the standard assumption that dermal melanin acts primarily as a sunscreen, suggesting, for example, a heat-absorbing or camouflage function. While few dermatologists seem aware of it, much relevant work has been done on the solid-state properties of melanin. Melanin is of great interest to solid-state physicists because it exhibits unique properties predicted by theory, but never previously found in any material.To summarize their findings as follows: melanin is a textbook example of an amorphous semiconductor, exhibiting such properties as threshold and memory switching.² A fundamental characteristic of an amorphous semiconductor is strong electron-phonon coupling. That is, energy readily transfers between phonons (eg, molecular vibrations, heat, and sound), and electronic vibrations (photons).For example, as Dr Morison notes, melanin efficiently converts light into heat—an electron-phonon conversion. Similar processes in the reverse