Melanin is a natural pigment found in most organisms, including humans, responsible for the coloration of hair, skin, and eyes. Specialized cells synthesize this substance to fulfill various biological functions. The amount and type of melanin produced are primarily determined by genetics, influencing a wide spectrum of physical traits.
Forms and Distribution in the Body
Melanin is a group of pigments, not a single compound, with three main forms recognized in humans. Eumelanin is the most common form, giving rise to brown and black hues in the skin, hair, and eyes. Pheomelanin is the second type, responsible for red and yellow colors, contributing to red hair and pinkish tones in the body.
Both eumelanin and pheomelanin are produced by melanocytes, cells located predominantly in the basal layer of the epidermis (the outer layer of the skin). Melanocytes also reside within hair follicles and the iris of the eye, determining the color of those structures. A third type, neuromelanin, is found in the brain, coloring specific neurons in areas like the substantia nigra.
All humans possess a similar number of melanocytes. However, differences in skin, hair, and eye color result from the activity of these cells and the specific ratio of eumelanin to pheomelanin they produce. Melanocytes package the pigment into small sacs called melanosomes, which are then transferred to the surrounding skin cells. The size, number, and distribution of these melanosomes ultimately dictate an individual’s unique pigmentation.
Role in UV Protection and Pigmentation
The primary function of melanin is its role as a natural photoprotectant against ultraviolet radiation (UVR) from the sun. The pigment acts like a broadband absorber, absorbing UV light across the UVA and UVB spectrum. This process converts the energy into harmless heat, shielding the underlying skin cells from damage.
This protective mechanism is important for safeguarding the DNA within skin cells, as UV exposure can cause mutations leading to skin cancer. When melanocytes transfer melanosomes to the outer skin cells, the pigment accumulates like a cap over the cell nucleus, physically protecting the cell’s genetic material from harmful radiation.
The concentration and type of melanin directly influence an individual’s level of natural sun defense. Eumelanin is a more effective shield against UV damage than pheomelanin; individuals who produce more eumelanin generally have darker skin tones and a lower incidence of sun-related skin cancers. Conditions like albinism, which involve disrupted melanin production, leave affected individuals highly vulnerable to sun damage.