Melanin is a complex polymer derived from the amino acid tyrosine. It is the primary pigment responsible for the diverse range of skin and hair colors observed in humans. Its presence in the skin is a natural response to historical sun exposure, with varying degrees found across different populations.
Layers of epidermis. Structure of the human skin. Image Credit: Designua / Shutterstock
What is Melanin and How is it Produced?
Melanin biosynthesis is a multi-step process initiated by the enzyme tyrosinase, which catalyzes the chemical L-3,4-dihydroxyphenylalanine. A deficiency in tyrosine, the precursor amino acid, can result in albinism, a condition characterized by a lack of melanin. Melanin production occurs exclusively within specialized cells called melanocytes. Inside these cells, melanin pigment is stored in organelles known as melanosomes.
These melanosomes, filled with melanin, are then transported from melanocytes to other cells within the epidermis, the outermost layer of the skin. Melanin deposits, typically brown or black, are the key determinants of skin pigmentation. The shade of skin color varies significantly depending on the number and distribution of these melanosomes. Beyond skin color, melanin plays a crucial role in protecting cellular DNA from harmful ultraviolet (UV) radiation from the sun. Its protective properties are also being explored for potential applications in melanoma treatment.
Melanin is not limited to the skin and hair; it is found in various parts of the human body, including:
- Skin: Providing the basis for skin color.
- Hair: Contributing to hair color.
- Pupils and Irises of the Eyes: Determining eye color.
- Stria Vascularis of the Inner Ear: Functioning in auditory processes.
- Brain: Specifically in the substantia nigra and locus coeruleus regions.
- Adrenal Gland: Located in the medulla and zona reticularis.
Types of Melanin: Eumelanin, Pheomelanin, and Neuromelanin
Melanin is not a single entity but encompasses different types, each with unique characteristics and functions. The primary types include eumelanin, pheomelanin, and neuromelanin. Eumelanin is predominantly found in hair, skin, and the areolae around nipples. It is the most prevalent type in individuals with darker skin tones, imparting black and brown pigments to hair, skin, and eyes. When eumelanin is present in smaller quantities, hair color can range to blonde shades.
Pheomelanin is another type found in hair and skin. It is responsible for pink and red hues and is the primary pigment in individuals with red hair. Notably, pheomelanin offers less protection against UV radiation-induced skin cancer compared to eumelanin.
Neuromelanin is a specialized form of melanin located in specific brain regions. Research suggests that the loss of neuromelanin may be associated with the development of several neurological disorders, highlighting its importance in brain health.
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Further Reading
