[2] Melanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the amino acid tyrosine is followed by polymerization.

Pheomelanin is a cysteinated form containing polybenzothiazine portions that are largely responsible for the red or yellow tint given to some skin or hair colors.

The phenotypic color variation observed in the epidermis and hair of mammals is primarily determined by the levels of eumelanin and pheomelanin in the examined tissue.

[10] Because of this property, eumelanin is thought to protect skin cells from UVA and UVB radiation damage, reducing the risk of folate depletion and dermal degradation.

Exposure to UV radiation is associated with increased risk of malignant melanoma, a cancer of melanocytes (melanin cells).

[12] Analysis of highly pigmented (Fitzpatrick type V and VI) skin finds that DHI-eumelanin comprises the largest portion, approximately 60–70%, followed by DHICA-eumelanin at 25–35%, and pheomelanin only 2–8%.

[12] In chemical terms, pheomelanins differ from eumelanins in that the oligomer structure incorporates benzothiazine and benzothiazole units that are produced,[17] instead of DHI and DHICA, when the amino acid L-cysteine is present.

Pheomelanins, unlike euemanins, are rare in lower organisms[18] with claims they are an "evolutionary innovation in the tetrapod lineage"[19] but recent research finds them also in some fish.

[21] The biological function remains unknown, although human NM has been shown to efficiently bind transition metals such as iron, as well as other potentially toxic molecules.

This lead to a proposed biosynthetic process involving the hydroxylation of tyrosinylated peptides formed via proteases during sporogenesis, which are then incorporated autoxidatively into a growing L-DOPA core polymer.

[24] Due to selenium's higher atomic number, the obtained selenomelanin can be expected to provide better protection against ionising radiation as compared to the other known forms of melanin.

[25] Trichochromes (formerly called trichosiderins) are pigments produced from the same metabolic pathway as the eumelanins and pheomelanins, but unlike those molecules they have low molecular weight.

Melanins also protect microorganisms, such as bacteria and fungi, against stresses that involve cell damage such as UV radiation from the sun and reactive oxygen species.

Melanin also protects against damage from high temperatures, chemical stresses (such as heavy metals and oxidizing agents), and biochemical threats (such as host defenses against invading microbes).

Within minutes after infection, the microbe is encapsulated within melanin (melanization), and the generation of free radical byproducts during the formation of this capsule is thought to aid in killing them.

[43] Melanin in arthropods has been observed to be deposited in layers thus producing a Bragg reflector of alternating refractive index.

In both yellow and white male phenotypes of the wood tiger moth, individuals with more melanin had a heightened ability to trap heat but an increased predation rate due to a weaker and less effective aposematic signal.

[49] Biosynthesis involves the oxidation of indole-5,6-quinone by the tyrosinase type polyphenol oxidase from tyrosine and catecholamines leading to the formation of catechol melanin.

This differentiates melanin from common blood breakdown pigments, which are larger, chunky, and refractile, and range in color from green to yellow or red-brown.

In addition, two forms of albinism, with approximately 1 in 2,700 most prevalent among people of Puerto Rican origin, are associated with mortality beyond melanoma-related deaths.

In Parkinson's disease, a disorder that affects neuromotor functioning, there is decreased neuromelanin in the substantia nigra and locus coeruleus as a consequence of specific dropping out of dopaminergic and noradrenergic pigmented neurons.

Effective in treating white skin, in general, lasers are less successful in removing port-wine stains in people of Asian or African descent.

Higher concentrations of melanin in darker-skinned individuals simply diffuse and absorb the laser radiation, inhibiting light absorption by the targeted tissue.

In general, people whose ancestors lived for long periods in the regions of the globe near the equator have larger quantities of eumelanin in their skins.

This makes their skins brown or black and protects them against high levels of exposure to the sun, which more frequently result in melanomas in lighter-skinned people.

[66] Early humans evolved dark skin color, as an adaptation to a loss of body hair that increased the effects of UV radiation.

Following migration and settlement in Asia and Europe, the selective pressure dark UV-radiation protecting skin decreased where radiation from the sun was less intense.

Dark-skinned people, who produce more skin-protecting eumelanin, have a greater protection against sunburn and the development of melanoma, a potentially deadly form of skin cancer, as well as other health problems related to exposure to strong solar radiation, including the photodegradation of certain vitamins such as riboflavins, carotenoids, tocopherol, and folate.

However, the lens also becomes more rigid with age, losing most of its accommodation—the ability to change shape to focus from far to near—a detriment due probably to protein crosslinking caused by UV exposure.

This hypothesis is supported by the fact that the loss of neuromelanin, observed in Parkinson's disease, is accompanied by an increase in iron levels in the brain.