Melanin

Melanin is a family of special chemicals called biomolecules that give color to the skin, hair, and eyes of many living things. These chemicals are made in cells called melanocytes through a process known as melanogenesis. There are five main types of melanin: eumelanin, pheomelanin, neuromelanin, allomelanin, and pyomelanin. Eumelanin and pheomelanin are most important for the color of human skin and hair.

Eumelanin is mostly found in areas of the body that need protection from the sun, like the outer layer of skin and the part of the eye called the retinal pigment epithelium. It helps protect skin cells by absorbing over 99.9% of harmful UV radiation, which can damage the skin. Pheomelanin gives a red or yellow color to hair and skin. The balance between these two types of melanin helps determine a person’s natural skin tone.

Exposure to UV radiation can start the production of melanin, causing the skin to darken as a protective response. While melanin offers important protection against sun damage, too much exposure to UV radiation can still lead to health problems, including melanoma, a type of skin cancer. People with more melanin, and therefore darker skin, often have a lower risk of developing skin cancer.

Melanin types

Melanin comes in different types, each giving color to parts of our bodies. One type is called eumelanin, which can be dark brown or black and is found in skin and hair. Another type is pheomelanin, which gives a yellowish to reddish color, often seen in red hair and lips.

There are also special types of melanin like neuromelanin, found in the brain, and other rarer forms such as allomelanin and pyomelanin. These different types of melanin help protect our cells and give us our unique colors.

Main article: Neuromelanin

Humans

In humans, melanin helps determine skin color and is also found in hair, the colored part of the eye, and parts of the inner ear and brain. It is made by special cells called melanocytes in the skin’s bottom layer. While most people have about the same number of these cells, they can produce different amounts of melanin, leading to varied skin colors. Two main types of melanin are eumelanin, which is most common, and pheomelanin. Some people have a condition called albinism, where their bodies make very little or no melanin.

Other organisms

Melanins play many important roles in different living things. For example, some sea creatures like octopuses use a kind of melanin to make ink that helps them hide from predators. In tiny organisms like bacteria and fungi, melanin helps protect them from harmful sun rays and other damaging forces.

In animals, melanin helps give color to fur, feathers, and scales, and it can even help some animals stay warm. Plants also produce melanin, which can be seen when fruits brown after being cut. This melanin can help protect plants and give them color too.

Interpretation as a single monomer

Melanins are complex chemicals and do not have just one structure or exact makeup. Some chemical databases list a specific formula, like C₁₈H₁₀N₂O₄, to describe some of melanin’s properties. However, this simple formula is not likely to exist in nature by itself.

Biosynthetic pathways

The process that creates eumelanins and pheomelanins starts with an important enzyme called tyrosinase. This enzyme helps change a substance called tyrosine into another substance named DOPA, which then turns into dopaquinone.

Dopaquinone can mix with a molecule called cysteine to form pheomelanins, or it can change into another substance called leucodopachrome to eventually make eumelanins. These steps show how our bodies create the pigments that give color to skin, hair, and eyes.

Microscopic appearance

Melanin looks brown and is made of tiny granules, each smaller than 800 nanometers. This makes it different from other pigments from broken blood, which are larger, chunky, and can be green, yellow, or red-brown. In areas with a lot of melanin, it can cover up other details that scientists usually see. A weak mix of a chemical called potassium permanganate can remove the color from melanin.

Genetic disorders and disease states

Albinism is a condition where there is less or no melanin in the skin, hair, and eyes. It can cause fair skin, light hair, and blue eyes. There are many types of albinism, and some happen more in certain groups of people. For example, one common type is more frequent in people of African or European descent. Albinism can also affect vision, making it harder to see clearly.

There is a link between albinism and hearing problems in some people, though scientists do not fully understand why. In some rare cases, people with albinism may also have hearing loss. Melanin also plays a role in other conditions, such as Parkinson's disease, where there is a decrease in a type of melanin in the brain.

Human adaptations

Melanocytes are special cells that produce melanin and place it into tiny packages called melanosomes. These melanosomes move into skin cells, where they gather above the cell nucleus. This protects the DNA inside from damage caused by the sun's ultraviolet rays. People from areas near the equator usually have more melanin, giving their skin a brown or black color, which helps shield them from strong sunlight.

As humans moved to places with less sunlight, their skin lightened to help their bodies make more vitamin D. Light skin also helps people stay cooler in hot weather. When skin is exposed to the sun, it often darkens, which is called tanning. This extra melanin helps protect against sunburn and skin cancer. Melanin in the eyes also helps shield them from harmful light.

Physical properties and technological applications

Melanin is a special kind of material that can help protect cells from damage caused by tiny particles called free radicals. Scientists think that the bigger and more connected the melanin molecules are, the better they work as a shield. When melanin doesn’t form properly, it might contribute to certain health problems in the eyes and skin.

In cases of a type of skin cancer called melanoma, the stiffness of the cancer cells plays a role in how the disease spreads. Pigmented melanoma cells are stiffer than non-pigmented ones, which may affect how easily the cancer grows and spreads. Both types of cells can resist treatment and spread, making this a challenging disease to manage.