The cells in the skin that produce melanin are called melanocytes, which literally mean "melanin cells". Melanin is one mechanism that protects the body from the harmful effects of sunlight. Exposure to sunlight triggers the melanocytes which produce melanin, darkening the skin. Most people relate to this as "tanning".
In addition to tanning, melanocytes produce the melanin that gives hair and eyes their color. According to Encyclopedia of Health, everyone has the same number of melanocytes regardless of natural coloration. What makes the difference between skin, eye or hair tones is how active those melanocytes are in producing melanin. Also, the type of melanin produced causes variation in coloration. Genetics figures prominently in the triggering of melanocytes and type of melanin produced.
The mechanism by which melanocytes are triggered is different depending on if the cause is exposure to sunlight or genetics. to sunlight causes cell damage which releases biochemicals that trigger the pituitary gland to produce melanin stimulating hormone (MSH). MSH then triggers melanin production in the melanocytes. variations in coloration are caused by variations in the level of the production of an enzyme called tyrosinase. Tyrosinase is the building block for melanin, so the more tyrosinase available the greater the production of melanin.
The two types of melanin are and pheomelanin. The shade of melanin produced is the difference between these types of melanin with eumelanin being the brown to black melanin and pheomelanin being the yellow to red melanin. All melanocytes have the ability to produce both types of melanin but the amount of each is controlled by receptors on the melanocytes and the biochemical that trigger them.
During embryonic development, the melanocytes are formed and migrate towards the bottom layer of the skin, called the basal layer. According to the Academy of Dermatology, there is a ratio of 1 melanocyte to every 10 skin producing, or keratinocytes, cells. The lone melanocyte is then able to produce melanin for up to approximately 30 keratinocytes. The keratinocytes then produce the skin cells that move to the top layer of the skin, carrying the melanin with them.
There are many ways that the production of melanin can be altered, resulting in skin disorders. Improper melanocyte formation, inadequate supply of enzymes to build the melanin, improper triggering biochemical production, and extensive damage to the skin from burns or exposure to excessive amounts of ultraviolet light can all result in melanin production dysfunction. Some conditions associated with altered melanin production include: albinism (complete lack of pigmentation), vitiglio (an autoimmune disorder), hyper- and hyp- pigmentation disorders (in general), and melanoma (a form of skin cancer specific to melanocytes). Thankfully, most of these conditions are surprisingly rare. However, according to the Department of Health melanoma cases are steadily increasing. Melanoma spreads quickly and is the most lethal of all forms of skin cancer.