Melanin: Functions, Types & Benefits

Melanin is a naturally occurring pigment that gives colour to skin, hair and eye. Different people have different levels of melanin because of their genetics and other factors like sun exposure and the amount of melanin content found in their ancestors.

The chemical formula for melanin is C₁₈H₁₀N₂O₄. Every person's melanin is produced at a different rate and in a different amount, regardless of having an equivalent number of melanocytes. 

In animals, melanin can be found in feathers, scales and internal membranes like the peritoneum. In humans, they appear as diffuse spots in the epidermis, melanocytes of dark-skinned people and in dark skin tags.

Key Terms: Melanin, Melanocytes, Pigmentation, UV Rays, Eumelanin, Pheomelanin, Neuromelanin.

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What is Melanin?

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Melanin can be defined as a naturally occurring pigment responsible for the unique hair, eyes and skin colour in humans and other animals. 

• Melanin is produced by melanocytes (skin cells) as an end product during tyrosine metabolism. It is a complex polymer with the chemical formula C₁₈H₁₀N₂O₄. 
• Despite having an equal number of melanocytes, each person's melanin is produced at a different rate and in a different amount. 
• The amount and density of melanin pigment in an animal's body determine its colour. 
• Other than colour, it also provides protection from sunlight to the eyes and skin.
• Melanogenesis is the process by which melanin is formed in the skin cells. The process involves tyrosine being synthesized and oxidized, followed by polymerization.

Structure of Melanin

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Types of Melanin

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The term melanin refers to a group of organic pigments that are present in most organisms. It is of three types:

Eumelanin

It is responsible for the dark colour of skin, eyes and hair. 

• It is an inert pigment which can efficiently absorb UV light as it is present in the epidermis. 
• The amount of eumelanin in the interfollicular epidermis directly relates to skin colour. 
• Keratinocytes are the cells that carry eumelanin to the skin surface. 
• Black and brown are the two types of eumelanin present. 
• Different amount of eumelanin was observed in individuals with black or brown hair. 
• Blonde hairs are formed when black eumelanin is absent and brown eumelanin is present in trace amounts.

Pheomelanin 

Pheomelanin is the type of melanin that gives colour to lips, nipples and other reddish-pink-coloured body parts. 

• It is also found in red hairs, feathers and freckles. 
• People with lots of pheomelanin are observed to have lighter skin tones.
•  Like eumelanin, it is also present in the epidermis. 
• Pheomelanin production can lower glutathione levels and increase melanocytes' susceptibility to genetic instability and DNA damage.

Neuromelanin 

Neuromelanin is a dark pigment present in the brain and confers colour to the neurons. 

• Its large quantities are found in catecholaminergic cells of the substantia nigra pars compacta and locus coeruleus, giving a dark colour to the structures.
• It inactivates oxidative stress causing iron ions, thus playing a protective role. 

Types of Melanin

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Functions of Melanin

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Broad biological functions of melanin include pigmentation of hair, eyes, and skin and protecting skin and eyes from the sunlight. Some main functions of melanin are as follows - 

• Protection of skin from UV-A rays. UV rays stimulate melanin function which acts as a barrier for the skin.
• Deranged beams of light get absorbed by melanin which improves vision.
• In cold-blooded animals, it absorbs heat within the skin to help them survive in cold weather.
• It provides cover for some animals that become active around dusk.
• Melanin acts as camouflage in certain animals improving their survival and adaptability.
• It protects organisms and aids in their adaptation by acting as a resistance to abrasion in an unfavourable environment.

Different proportions of melanin forms result in various hair colours - 

• Black - A large quantity of eumelanin.
• Brown - Moderate quantity of eumelanin. 
• Blonde - Eumelanin in little quantity.
• Red - Large quantity of pheomelanin, with trace amounts of eumelanin.

Melanin Production Sites

Melanin is housed in melanosomes, which are cells in melanocytes. These cells are located in the following parts of the body - 

• The innermost layer of the skin
• Pupils and irises
• Hairs
• The stria vascularis of your cochlear duct (part of the inner ear)
• The medulla and zona reticularis (areas of the adrenal gland)
• The substantia nigra and locus coeruleus (areas of the brain)

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Benefits of Melanin

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There are several benefits of Melanin, including:

• Protection Against Reactive Oxygen Species (ROS) - reactive oxygen species (ROS) are formed as by-products of bodily cell processes. ROS can cause stress, premature ageing and damage when accumulated in the cells. They can also be linked with health concerns like cancer and diabetes. Melanin scavenges ROS formed from oxidative stress by UV light on the skin and eliminates them.
• Protection from UV Rays - being a UV-absorbing agent, it protects skin from the harmful effects of sunlight. Eumelanin absorbs UV-B. It also offers protection against blue light.

Melanin also aids in the proper function of the immune system and reduces inflammation in the body. A study in rats shows its ability to prevent stomach ulcers in rats.

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Hyperpigmentation and Hypopigmentation

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Excess production of melanin within the body is called hyperpigmentation. The presence of the excess melanocyte-stimulating hormone (MSH) leads to this condition. Other conditions that increase melanin amount in the skin are sun exposure, hemochromatosis, Addison’s disease and pregnancy.

When the amount of melanin in the body is very less or is in trace amounts, this condition is called hypopigmentation. It results in vitiligo (white patches on the skin) and albinism (little to no melanin in eyes, skin or hair).

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Melanin Disorders

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Melanin deficiency can lead to many skin problems and health conditions. Some of them are as follows:

• Albinism - This disorder occurs when a person has very less melanin present in the body. Affected individuals have white hair, pale skin and blue eyes with an increased risk of vision loss and sun damage.
• Melasma - Melasma-affected individuals have blue-grey or brown patches on arms and faces. Caused by sun exposure and hormone imbalance. 
• Vitiligo - Melanocytes get destroyed by the immune system resulting in white patches on the skin. It is more noticeable in dark-skinned people.
• Parkinson’s disease - Brain cells in substantia nigra die in affected individuals leading to a decrease in neuromelanin.
• Hearing Loss - Melanin is linked to hearing loss as it is found in the stria vascularis of the inner ear. Individuals with little melanin have higher risks of hearing loss.
• Pigment Loss - Burnt, blistered and infected skin may be unable to produce melanin again. 

Sources of Melanin 

Antioxidants, botanicals and Vitamins like A, C and E are the main sources of melanin. The main food sources of melanin are colourful vegetables, carrots, citrus, dark chocolate, dark berries, essential oils, grains, nuts, peas, seeds, spinach, tea and vitamin supplement. 

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Things to Remember 

• Melanin is a naturally occurring pigment responsible for the color of hair, eyes and skin. 
• Melanin is of three types: Eumelanin, Pheomelanin and Neuromelanin.
• Melanin provides protection against reactive oxygen species, UV rays and many health conditions.
• When melanin is produced in excess, it is known as hyperpigmentation. 
• Hypopigmentation is the condition in which it is produced in very low quantities.
• Vitiligo, albinism and melasma are some of the major disorders related to melanin.

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