Eumelanin is a natural pigment found in humans and many other animals. It is the most abundant form of melanin and is responsible for producing brown and black colors. The amount of eumelanin is determined by genetic factors and the sun exposure of ancestral populations.
The Role of Eumelanin in Pigmentation
The primary function of eumelanin is to provide pigmentation to the hair, skin, and eyes. Higher amounts of eumelanin result in darker coloration. For instance, black and brown hair are the result of different combinations and quantities of black and brown eumelanin. A very small amount of brown eumelanin, in the absence of black eumelanin, produces blonde hair.
Skin color is also determined by the amount of eumelanin. Individuals with darker skin have a higher concentration of this pigment. While all humans have a similar number of melanin-producing cells, the level of production varies. This variation accounts for the wide spectrum of human skin tones.
In the eyes, eumelanin creates brown coloration. The amount of this pigment in the iris, along with the density of its granules, dictates the final eye color. This interplay results in the diverse range of brown hues seen in human eyes.
How Eumelanin is Produced
Eumelanin is synthesized through a multi-step process known as melanogenesis. This biological pathway takes place within specialized cells called melanocytes, located in the skin and hair follicles. The production of eumelanin is initiated in response to triggers, most notably exposure to ultraviolet (UV) radiation from the sun.
The synthesis of eumelanin begins with the amino acid tyrosine. Through a series of chemical reactions catalyzed by enzymes, tyrosine is transformed into eumelanin. An important enzyme in this process is tyrosinase. A defect in the production of tyrosinase can disrupt the entire melanin production pathway, leading to conditions such as albinism.
The initial product of the enzymatic reaction is a molecule called dopaquinone. This molecule can then be converted into two main types of eumelanin: a dark brown or black form and a lighter, more soluble form. These two forms can combine in different proportions, contributing to the wide variety of brown and black shades seen in human pigmentation.
Eumelanin’s Protective Functions
Beyond its role in pigmentation, eumelanin serves a protective function. Its primary role is photoprotection, or protection against the harmful effects of sunlight. Eumelanin is highly effective at absorbing and scattering ultraviolet (UV) radiation, dissipating over 99.9% of it. This prevents UV radiation from penetrating deeper into the skin and damaging the DNA of skin cells.
This absorption of UV rays helps reduce the risk of skin cancers like malignant melanoma. Individuals with darker skin tones, who have higher concentrations of eumelanin, have a lower incidence of skin cancer. In response to sunlight, the body increases melanin production, leading to a tan, which is a natural defense mechanism against further sun damage.
Eumelanin also has antioxidant properties, neutralizing unstable molecules called reactive oxygen species (ROS). An accumulation of ROS can lead to cellular stress, aging, and various diseases. By scavenging these molecules, eumelanin helps protect cells from damage.
Eumelanin vs. Pheomelanin
Eumelanin is one of two main types of melanin found in humans; the other is pheomelanin. Pheomelanin is responsible for producing the red and yellow pigments seen in hair and skin. This type of melanin is what gives red hair its characteristic color and contributes to the pinkish hue of lips and nipples.
The spectrum of human hair and skin color is determined by the ratio of eumelanin to pheomelanin, as well as the total amount of melanin. For example, an individual with red hair has a relatively equal amount of both pheomelanin and eumelanin. In contrast, black hair is composed of about 99% eumelanin.
This balance between the two types of melanin is genetically determined. Unlike eumelanin, pheomelanin does not offer the same level of protection against sun damage.