Melanin

Melanin is a special kind of chemical that gives color to the skin, hair, and eyes of many living things. These chemicals are made in cells called melanocytes.

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 found in parts of the body that need protection from the sun, like the outer layer of skin. It helps protect skin cells by absorbing harmful UV radiation. Pheomelanin gives a red or yellow color to hair and skin. The balance between these two types of melanin helps decide a person’s natural skin tone.

When the skin is exposed to UV radiation, it can make more melanin. This can cause the skin to darken as a way to protect itself. While melanin helps protect the skin, too much UV radiation can still cause health problems.

People with more melanin, and darker skin, often have a lower risk of developing skin problems.

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. These different types of melanin help protect our cells and give us our unique colors.

Main article: Neuromelanin

Humans

In humans, melanin helps decide skin color. It is also in hair, the colored part of the eye, and parts of the inner ear and brain. Melanin is made by special cells called melanocytes in the bottom layer of the skin. Most people have about the same number of these cells, but they can make different amounts of melanin. This leads to different skin colors. There are two main types of melanin: eumelanin, which is most common, and pheomelanin. Some people have a condition called albinism. In albinism, the body makes very little or no melanin.

Other organisms

Melanins are important for many living things. Some sea creatures like octopuses use a kind of melanin to make ink that helps them hide. In tiny organisms like bacteria and fungi, melanin helps protect them from sun rays and other harmful forces.

In animals, melanin helps give color to fur, feathers, and scales. It can also help some animals stay warm. Plants make melanin too. You can see it when fruits brown after being cut. This melanin helps protect plants and give them color.

Interpretation as a single monomer

Melanins are complicated chemicals. They don’t have just one structure or exact makeup. Some chemical lists might show a simple formula, like C₁₈H₁₀N₂O₄, to explain some of melanin’s traits. But this simple formula probably doesn’t exist in nature on its own.

Biosynthetic pathways

The process that makes eumelanins and pheomelanins starts with an 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 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 pieces, each smaller than 800 nanometers. This makes it different from other pigments that come from broken blood. Those pigments are bigger and can be green, yellow, or red-brown. In places with a lot of melanin, it can hide other details that scientists want to see. A weak mix of a chemical called potassium permanganate can take the color away from melanin.

Genetic disorders and disease states

Albinism is a condition where there is less or no melanin in the skin, hair, and eyes. This can cause fair skin, light hair, and blue eyes. There are many types of albinism. Some types 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.

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 make melanin. They put melanin into tiny packages called melanosomes. These melanosomes move into skin cells and gather above the cell nucleus. This helps protect the DNA inside from the sun's ultraviolet rays.

People who live near the equator usually have more melanin. This gives their skin a brown or black color and helps protect them from strong sunlight.

When humans moved to places with less sunlight, their skin lightened. This helped 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. This is called tanning. The extra melanin helps protect against sunburn and skin problems. Melanin in the eyes also helps protect them from bright light.

Physical properties and technological applications

Melanin is a special material that helps protect cells from tiny particles called free radicals. Scientists think that when melanin molecules are bigger and more connected, they work better as a shield. If melanin doesn’t form properly, it might cause health problems in the eyes and skin.

In some cases of skin cancer called melanoma, the stiffness of the cancer cells can affect how the disease spreads. This makes it hard to treat.