Melanin
Where does skin color come from?
A cell is primarily made of water, lipids, and proteins, so most cells are transparent. Our bodies, despite being made up of cells, are not transparent. In most mammals, skin, fur, and hair coloration are caused by a pigment called melanin.
Melanin comes in two main forms.
Eumelanin is a black or brown pigment and constitutes about 74% of the melanin in human skin
Eumelanin causes darker skin, hair, and eyes and has photoprotective properties. UV-radiation can cause breakages in DNA strands which can lead to skin cancers such as basal cell carcinoma or melanoma. Additionally, UV radiation can create reactive oxygen species such as hydroperoxyl (HO2) which can interfere with biological functions. Eumelanin can act as a physical barrier that absorbs and scatters UV radiation before it can reach the DNA. As a result, individuals with light skin are about seventy times more likely to develop skin cancer than individuals with darker skin.
Pheomelanin is a red or yellow pigment and is responsible for about 26% of melanin.
Pheomelanin, on the other hand, is a red and yellow pigment. In humans it can appear as red hair (blonde hair is caused by low overall melanin levels). Unlike eumelanin, pheomelanin is prone to degradation by UV light which can create hydrogen peroxide anions. This has negative effects on the skin and can result in increased cell death upon experiencing UV radiation. Pheomelanin is can cause increased histamine release which results in skin redness, especially in lighter skinned individuals.
Other forms of melanin include neuromelanin which colors the brain. Neuromelanin may be associated with neuroprotective effects as it is found in lower levels in Parkinson’s Disease patients. Additionally, neuromelanin is more prevalent in humans than any other primate.
Overall, melanin can cause a wide variety of effects in the body, including, but not limited to coloring our cells.
References
Nguyen, D. H. (n.d.). What colors are the cells in your body? Seattle PI. https://education.seattlepi.com/colors-cells-body-5632.html (Seattle PI - Education)
Nasti, T. H., & Timares, L. (2015). MC1R, eumelanin and pheomelanin: Their role in determining the susceptibility to skin cancer. Photochemistry and Photobiology, 91(1), 188–200. https://doi.org/10.1111/php.12335 (PMC)
Cleveland Clinic. (n.d.). Melanin: What is it, types & benefits. Cleveland Clinic. https://my.clevelandclinic.org/health/body/22615-melanin
D’Mello, S. A. N., Finlay, G. J., Baguley, B. C., & Askarian-Amiri, M. E. (2016). Signaling pathways in melanogenesis. Pigment Cell & Melanoma Research, 29(5), 528–540. https://doi.org/10.1111/pcmr.12410
Slominski, A., Tobin, D. J., Shibahara, S., & Wortsman, J. (2004). Melanin pigmentation in mammalian skin and its hormonal regulation. Physiological Reviews, 84(4), 1155–1228. https://doi.org/10.1152/physrev.00044.2003
Ito, S., & Wakamatsu, K. (2005). Chemistry of mixed melanogenesis—Pivotal roles of dopaquinone. Pigment Cell Research, 18(4), 264–272. https://doi.org/10.1111/j.1600-0749.2005.00244.x