About Melanin and Skin color

Melanin is a biological pigment that can be found in hair, the eyes, the ear, the brain and other parts of the human body. Melanin is water-insoluble polymer of various compounds derived from the amino acid tyrosine. Skin color comes from a pigment called melanin. This pigment is made by melanocytes, a type of cell deep within the skin. It is one of two pigments found in human skin and hair and adds brown to skin color; the other pigment is carotene, which contributes yellow coloring. The synthesis of melanin reactions is catalyzed by the enzyme tyrosinase.Tyrosinase is found in only one specialized type of cell, the melanocyte, and in this cell melanin is found in membrane-bound bodies called melanosomes. Melanosomes can be transferred from their site of synthesis in the melanocytes to other cell types. The various hues and degrees of skin tone or color found in the skin of human beings are directly related to the number, size, and composition of melanosomes within the melanocytes and distribution of melanocytes or activity of melanogenic enzymes. Besides it role in pigmentation, melanin, which absorbs ultraviolet light, plays a protective role when skin is exposed to the damaging rays of the sun. Melanocytes convert an amino acid called tyrosine into melanin. It uses an enzyme called tyrosinase to do this.These pigments are then transported to the upper layers of the skin where they are deposited. The more melanin is produced, the darker your skin gets.There are three main types of melanin. Eumelanin, pheomelanin and neuromelanin. In context to the human skin color, Melanin comes mainly in two forms. It can be a lighter, yellowish Pheomelanin or a darker brown Eumelanin.

Eumelanin is the most abundant type of melanin in humans. It can be found in two variations. Black eumelanin and brown eumelanin.

Pheomelanin is a red-yellow pigment found both in lighter-skinned humans and darker skinned humans. it contains sulphur and is alkali soluble.

Neuromelanin can be found in the medulla, the adrenal gland and pigment bearing neurons (locus coeruleus, substantia nigra, etc.) in the brain.

Melanin possesses photochemical qualities that makes it an excellent photoprotectant. The protective qualities of melanin rely upon its ability to absorb harmful UV-radiation and transform the solar energy into harmless heat. Melanin can dissipate the absorbed UV radiation as heat. This prevents the indirect DNA damage that is responsible for the formation of malignant melanoma and other skin cancers.

Interestingly UV radiation, when it comes in contact with pheomelanin, it possesses the ability of inducing the release of free radicals in the skin, thus intensifying skin damage rather than protecting the skin.

Upon exposure to UV radiation, DNA damage triggers cytokines, growth factors and other inflammatory factors to stimulate melanin production. Melanin forms in specialised cells called melanocytes. Melanocytes are especially abundant in the basal layer of the epidermis and underlying dermis and are responsible for the pigmentation of the skin. The melanocytes, by increasing the production of intracellular nitric oxide (NO), they trigger signal transduction cascades to initiate melanogenesis through a series of oxidative reactions involving the amino acid tyrosine in the presence of the enzyme tyrosinase. This leads to the production of melanin. Melanin granules synthesized in the melanocytes are then transferred from the cytoplasm of the melanocytes to the basal cytoplasm of the keratinocytes. In the human epidermis, melanocytes work in close harmony with their neighbouring cells such as keratinocytes via their dendrites. They thus form a protective covering in the inner layers of the epidermis, absorbing UV rays and inhibiting their penetration.