Melanin production, which is carried out by specialized basal cells in the epidermis called melanocytes, serves primarily to protect the skin and the nuclei of skin cells from the harmful UV component in sunlight. The melanocytes are able to synthesize the skin pigment melanin from the non-essential proteinogenic amino acid L-tyrosine. Secondarily, the individual composition of melanins influences hair and eye color.
What is melanin production?
Melanin production, which occurs through specialized basal cells in the epidermis called melanocytes, primarily serves to protect the skin and the nuclei of skin cells from the harmful UV component in sunlight. Melanin production is the biocatalytic synthesis of melanin by melanocytes. The melanocytes are located directly on the basement membrane, the lowest layer of the epidermis, and supply the keratinocytes with the pigment melanin, whereby a melanocyte supplies several keratinocytes simultaneously via cell extensions (dendrites). In the course of their life cycle, which lasts approximately 28 days, the keratinocytes gradually migrate from the basement membrane to the uppermost layer of the skin, where they are exfoliated as tiny horny platelets. Melanin production by melanocytes is mainly controlled by incident UVB light. In humans, melanin consists of a mixture of brownish to blackish eumelanins synthesized from the non-essential proteinogenic amino acid L-tyrosine and levodopa and yellowish to reddish sulfur-containing pheomelanins. Melanocytes synthesize and “store” the formed melanin in small vesicles called melanosomes. The transfer of the color pigments to the keratinocytes takes place with the help of the melanosomes. The composition of the melanins produced, i.e. the mixing ratio between eumelanins and pheomelanins, is largely genetically fixed.
Function and task
The main function of melanin production in the epidermis is to protect the top layer of skin, the epidermis or epidermis, from damage caused by excessive UV radiation. The main task and function is performed by the melanocytes, which not only synthesize the color pigments, but also transfer them to the keratinocytes, where the melanin wraps itself protectively around the cell nucleus and also protects the other organelles from the harmful UV component of sunlight. The melanin-enriched keratinocytes make the skin appear darker and tanner. It takes several weeks before a complete “tan” of the skin is achieved, because the melanocytes can only ever supply the lowest layers of keratinocytes with melanin, and the lowest keratinocytes only “arrive” at the skin surface after 28 days. It is very likely that UV protection in red-haired and light-blond people with a particularly light skin type, whose melanins contain a high proportion of pheomelanins, have lower UV protection than dark-skinned people with dark brown or black hair. The immediate benefit of melanin production for humans is that melanin provides initial photoprotection immediately after strong UV exposure by converting the excited molecules into heat. This short-term photoprotection prevents the development of free radicals and so-called reactive oxygen species. Another fast-acting protection results from the immediate pigmentation after UV irradiation. In this case, the melanocytes have already supplied the skin cells with precursors of melanin beforehand, which is converted to protective melanin by the UV radiation, i.e. it does not have to be newly synthesized first. However, this protection is only slightly effective and reversible. Skin tanned in this way loses its color again after just a few days if no further UV radiation is applied. Longer-term and stronger protection results from continuous pigmentation of the epidermis when it is exposed to UV radiation almost daily.
Diseases and complaints
The most common diseases and complaints associated with melanin production are over- or under-functioning of melanocytes, which can be caused by too many or too few melanocytes or by a malfunction in the synthesis of melanin.In most cases, over- and also under-functioning become noticeable in the form of pigment disorders in the skin appearance, which occur due to inherited genetic defects or were acquired through external influences. A very rare complete loss of melanin production is so-called albinism, which manifests itself in extremely white skin that is highly sensitive to UV rays, as well as white hair and a pale gray eye color. A well-known pigment disorder that occurs mainly on the extremities, face and genital area is vitiligo, which usually begins in childhood and progresses gradually throughout life. The peculiarity is noticeable by irregular white patches on the skin. It is probably an autoimmune disease in the course of which destruction of melanocytes in certain skin regions occurs. Known hyperpigmentations are liver spots, freckles and age spots. All three types of pigmentary disorder are usually harmless and have only cosmetic effects. The occurrence of localized hyperpigmentation depends on many factors such as genetic predisposition and UV exposure. Age spots, which appear from the age of about over 40, can also occur as a side effect of certain medications and can be promoted by excessive alcohol consumption and cigarette smoking. Pigmentary disorders known as moles or birthmarks are due to congenital disorders or disorders acquired through stresses on the skin. Less harmless are malignant melanomas, which are malignant tumors that develop from degenerated melanocytes and tend to spread early to the lymphatic system. Melanomas can develop from altered moles or birthmarks, but can also occur in completely inconspicuous areas of the skin. Another type of tumor is basal cell carcinoma, which can form on the basal cells of the epidermis. Basal cell carcinomas are less prone to spread, making them easier to treat and therefore classified as semi-malignant tumors.
