Melanin

Melanin is a natural pigment found in many living things, including humans. It gives color to skin, hair, and eyes. There are different types of melanin. Eumelanin is usually dark, and pheomelanin 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 help decide our skin tone. Melanin also protects us from the sun’s harmful rays. When skin is exposed to UV radiation, it makes more melanin. This darkens the skin and helps shield it from damage. People with more melanin often have a lower risk of some skin problems. Melanin is also found in other places, like the brain, where it may help protect 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 bottom layer of skin. 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 are important for many living things. Some sea animals like octopuses use a special kind of melanin to make ink that helps keep them safe. In tiny living things such as bacteria and fungi, melanin works like a shield. It protects them from harmful sunlight, high temperatures, and other dangers.

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

Interpretation as a single monomer

Melanins are complex chemicals without one single structure. Scientists use a simple formula, like C₁₈H₁₀N₂O₄, to study them. This formula is just a model and not the real form melanin has in living things. This way of describing melanin began with an old report from 1948.

Biosynthetic pathways

The first step to make eumelanins and pheomelanins uses 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 and 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 cannot make enough melanin. This can cause fair skin, light hair, and bright blue eyes. It is more common in some groups of people. Albinism can also affect vision, making it harder to see clearly.

There are links between albinism and other health issues, such as hearing problems. Melanin also plays a role in other conditions, like Parkinson's disease. 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 put melanin into special bags called melanosomes. These bags move into skin cells. The granules gather above the cell’s core and shield important material from the sun’s strong rays.

People from areas near the equator usually have more of a type of melanin called eumelanin. This gives their skin a brown or black color and helps protect against sun damage.

As humans moved to places with less strong sunlight, their skin lightened. This change helped their bodies make more vitamin D, which is important for health. When skin is exposed to the sun, it often darkens. This is called a suntan and is the body’s way of increasing protection.

Darker skin helps prevent sunburn and some health issues from too much sun. Melanin also helps protect the eyes from bright light.

Physical properties and technological applications

Melanin is a special material that helps protect cells. Scientists believe that when melanin molecules are bigger and more connected, they work better as a shield. If conditions aren’t right for making melanin, it might not work as well and could cause problems in the eyes or skin.

In a skin condition called melanoma, the stiffness of the cells affects how it 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 might spread in the body.