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Melanin Production, Distribution & Function

People have skin that is white, black or yellow/orange in appearance, while some are said to have red skins. There are also subtle variations of the main colours, even amongst people of the same race, and interracial children develop unique skin colours that are based on their parents. There is also albinism, a special group of people with a skin disorder that makes them all look the same (in colour).

Why do we have all these different colours, and why do our skins respond differently when we are exposed to the sun and the elements? The answer is simple – melanin.

What is melanin?

This is the pigment that gives the skin its colour. It is produced by special cells called melanocytes during a process called melanogenesis. According to study.com, every human being has almost the same number of melanocytes. What differs in each person is the amount of melanin that is produced. The different shades of colours seen in different people are genetically determined. But there are other factors that determine the appearance of the skin, depending on the amount of melanin that is present. These factors include:

  • Exposure to sun rays (ultraviolet light – UVL). The more exposure a person has to UV light, the more melanin is produced. UV light induces free radicals that stimulate melanin synthesis by activating the tyrosinase mRNA (rate limiting enzyme for melanin synthesis). Hence, an antioxidant serum that is formulated with high strength L-ascorbic acid or glutathione at this stage helps. This is nature’s way of protecting the skin and the integrity of the DNA
  • The size of melanocytes – this differs between people, which affects the amount of melanin produced
  • The number of melanosomes (see below)
  • Pathological conditions of the skin, such as albinism and vitiligo, which are conditions caused by a lack of melanin and the gradual loss of melanocytes

There are many environmental factors that can determine the number of melanin deposits. Hormones can also play a role, including growth hormones and the hormonal changes that occur during pregnancy, which can lead to skin pigmentation in some women.

There are two types of melanin. These are:

  • Eumelanin: the commonest type of melanin. It is brownish in colour and said to offer better protection against UV rays
  • Pheomelanin: this type gives skin a reddish-brown colour and is also responsible for both red hair and freckles

The functions of melanocytes

  • They protect the skin by scattering UV light. A new study from the Lund University, Sweden, tries to explain how this protection occurs
  • Protect the skin from DNA damage by UV light
  • Deactivate harmful free radicals (reactive oxygen species)
  • Help to absorb and distribute heat
  • Protect cell membrane oxidation

Melanocytes produce melanin and transport it to the skin cells via arm-like structures called dendrites. The melanin pigments are contained in special organelles called melanosomes. The cells that receive the melanin are called keratinocytes, and the amount moved to them is demand driven. For example, if the skin is exposed to the sun (UV light), more melanin will move to the cells. This process also protects the DNA structure against UV rays damage.

What a suntan means

A suntan is a change that occurs when more melanin is released and taken up by keratinocytes. This is a protective response to prevent further damage to the skin. So, as admirable as having a tan is, it is a sign of skin pigmentation due to UV rays damage.

The difference between dark and light skins

The colour of dark skin is due to there being more melanin deposits in it which, in turn, is due to the melanocytes being larger. They also have more dendrites, which are larger and have more melanosomes.As a result, the overall amount of melanin transported to the keratinocytes is higher.

This offers more protection against UV rays and so dark-skinned people are better protected against photo ageing caused by these rays. This means dark skin photo ages slower than light skin. However, this doesn’t mean that dark or black skins are absolutely safe from the effects of UV rays, so the appropriate measure should always be taken against these rays.

On the other hand, light skins have:

  • Smaller melanocytes
  • Fewer dendrites (projections into the layers of the epidermis)
  • Smaller melanosomes
  • Fewer melanin deposits in the epidermal cells

The difference in the appearance of skin colour is also determined by the way the melanosomes are distributed. In white skins, melanin remains inside the melanosomes and is held together in the basal layer of the epidermis. Whereas in dark/black skins, melanosomes (that contain melanin pigments) move all the way to the upper part of the epidermis, where they burst and set free the melanin pigments into the keratinocytes cells. The melanin is distributed evenly, unlike in white skin.

Any changes in melanocytes production (melanogenesis) can determine the state of skin pigmentation. The distribution of melanin, and where it is deposited by the melanosomes, will also determine how the skin appears.

A summary of how skin pigments occur:

  • A person’s genetics determine the colour of the skin
  • The concentration and distribution of melanin pigments gives the skin its colour, from the fairest to the darkest and all the shades in between
  • The environment can determine the amount of melanin produced. More melanin is produced when it is exposed to UV rays. This is to protect the skin against free radicals, inflammation and burns,and the DNA against possible malignant changes
  • A suntan is a form of skin damage pigmentation that occurs with regular exposure to sunrays. It is associated with an increase in eumelanin, which offers better skin protection against cancerous changes
  • Skin burning occurs more often when there is irregular exposure to the sun, which increases the risk of malignant skin changes. Irregular exposure is also associated with an increase in pheomelanin levels
  • Although dark/black skins are better protected from UV rays than white skins, they are still at risk of skin damage, especially from UVA rays
  • Artificial UV rays have the same effects on the skin as natural UV sunrays
  • Cyanosis, erythema and pallor are other forms of skin pigmentation that are not directly related to the skin pigmentation process

If you spot any type of pigmentation that has no obvious cause or makes you anxious, report it to a skin specialist for assessment.

References

  • Slominiski A, Tobin DJ, Shibahara S. et al. ‘Melanin Pigmentation in Mammalian Skin and Its Hormonal Regulation.’ Phyiol. Rev. Vol 84, No. 4, pp 1155-1228. 2004
  • Videira, I. F. dos S., Moura, D. F. L., & Magina, S. (2013). ‘Mechanisms regulating melanogenesis.’ Anais Brasileiros de Dermatologia, 88(1), 76–83. http://doi.org/10.1590/S0365-05962013000100009
  • Lund University. ‘Skin pigment renders sun’s UV radiation harmless using projectiles.’ ScienceDaily. ScienceDaily, 26 September 2014.
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