Melanin

Melanin is a group of natural pigments found in many living things, including humans. It gives color to skin, hair, and eyes. There are different types of melanin, such as eumelanin, which is usually dark, and pheomelanin, which can be red or yellow. These pigments are made inside special cells called melanocytes through a process called melanogenesis.

In humans, the amount and type of melanin we have help determine our skin tone and protect us from the sun’s harmful rays. When skin is exposed to UV radiation, it makes more melanin, which darkens the skin and helps shield it from damage. People with more melanin in their skin often have a lower risk of certain skin cancers. Melanin is also found in other places, like the brain, where it may play a role in protecting nerve cells.

Melanin types

Melanin is a group of natural pigments that give color to skin, hair, and eyes. There are five main types of melanin. Eumelanin creates dark brown to black colors and is found in skin and hair. Pheomelanin gives a yellow to reddish color, often seen in red hair and lips.

Neuromelanin is a type of melanin found in certain brain cells and may help protect brain cells. Other types of melanin, like allomelanin and pyomelanin, are found in plants and fungi, showing the wide presence of these pigments in nature.

Humans

Melanin is what gives people their skin, hair, and eye color. It is made by special cells called melanocytes in the skin’s bottom layer. Different amounts of melanin make skin darker or lighter.

Even though everyone has about the same number of melanocytes, some people make more melanin than others. There are two main types of melanin in humans: eumelanin, which is most common, and pheomelanin. Some people have a condition called albinism where they make very little or no melanin.

Other organisms

Melanins play many important roles in different living things. For example, some sea animals like octopuses use a special kind of melanin to make ink that helps protect them from danger. In tiny living things such as bacteria and fungi, melanin acts like a shield, protecting them from harmful sunlight, high temperatures, and other damaging forces.

In animals like fish and birds, melanin helps give their skin and feathers color and also makes them stronger and more resistant to wear. In some insects, melanin can help them stay warm. Even plants can produce a type of melanin that gives fruits their brown color when they are cut open.

Interpretation as a single monomer

Melanins are complex chemicals that don’t have just one fixed structure. Scientists sometimes describe them using a simple formula, like C₁₈H₁₀N₂O₄, to help study their properties. However, this is just a model and not the actual form melanin takes in living things. This way of describing melanin started from an old report from 1948.

Biosynthetic pathways

The first step to make eumelanins and pheomelanins happens with a special helper called tyrosinase. This helps change tyrosine into DOPA and then into dopaquinone.

Dopaquinone can mix with cysteine to make pheomelanins, or it can change into other steps to make eumelanins. These steps include turning into things like leucodopachrome and dopachrome before finally becoming the pigments in our skin, hair, and eyes. You can find more details about these steps in the KEGG database.

Microscopic appearance

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

Genetic disorders and disease states

Albinism is a condition where the body does not make enough melanin. This can cause fair skin, light hair, and bright blue eyes. It is more common in some groups of people than others. For example, it happens more often in people of African descent and in some European groups. Albinism can also affect vision, making it harder to see clearly.

There are links between albinism and other health issues, such as hearing problems, though scientists are still learning why this happens. Melanin also plays a role in other conditions, like Parkinson's disease, where a type of melanin in the brain changes. Too much or too little melanin can affect how some treatments work, like laser therapy for skin conditions. Freckles and moles are caused by small collections of melanin in the skin.

Human adaptations

Melanocytes place granules of melanin into special bags called melanosomes, which move into skin cells. These granules gather above the cell’s core, shielding important material from the sun’s strong rays. People from areas near the equator usually have more of a type of melanin called eumelanin, giving their skin a brown or black color and helping protect against sun damage.

As humans moved to places with less strong sunlight, their skin lightened. This change allowed their bodies to make more vitamin D, which is important for health. When skin is exposed to the sun, it often darkens, known as a suntan, which is the body’s way of increasing protection. Darker skin helps prevent sunburn and some health issues from too much sun, such as a serious skin condition called melanoma. Melanin also helps protect the eyes from bright light.

Physical properties and technological applications

Melanin is a special kind of material that can help protect cells from damage. Scientists think that the bigger and more connected the melanin molecules are, the better they work as a shield. When conditions aren’t just right for making melanin properly, it might not work as well and could even cause problems in the eyes or skin.

In cases of a skin condition called melanoma, the stiffness of the cells plays a role in how the disease spreads. Cells with more melanin are stiffer and don’t spread as easily as cells with less melanin. Both types of cells can be hard to treat and can spread throughout the body.