The definition of melanin (not to be confused with melatonin) is that of a protein secreted by melanocytes. What is it for? It has the function of protecting the skin and eyes from damage caused by the sun’s UV rays, even through tanning.
The lack of melanin is responsible for white hair and white spots on the skin.
What to eat to increase melanin? Foods that provide the precursors necessary for its synthesis (soy, beans, Parmesan cheese, meat, egg whites, …) and carrots and other yellow and orange vegetables, rich in beta-carotene, which help darken the skin. The same substances can be integrated with products in capsules or tablets called “tan activators”.
Protecting yourself with cosmetics containing SPF is always essential, especially for children and pregnant or breastfeeding women at risk for melasma.
What is melanin and its relationship to the skin?
The term melanin comes from the Greek word μέλας, which means black. Melanin is in fact the brown pigment that helps determine the color of the skin, eyes and hair.
What is it for? Through its darkening action, it protects the skin and eyes from the aggressive action of the sun’s rays.
Its synthesis (melanogenesis) is activated by the sun and takes place in cells (melanocytes) present in the deep layers of the skin, in the iris of the eyes and in the hair follicle. Their number is more or less always the same, but the amount of melanin they produce changes: this explains why some people have a dark phototype and others a light one.
There are several subtypes: the main ones are eumelanin (beige, blond or darker and brown in color) and pheomelanin (red melanin).
Melanin is at the center of several disorders that interfere with its production. The quantity that is synthesized can be insufficient (hypopigmentation or depigmentation) or, on the contrary, excessive (hyperpigmentation) and both phenomena can concern limited areas or be spread over the entire surface of the body.
Furthermore, its chemical structure can be altered due to genetic causes. Dermatology mainly deals with these disorders, even if their diagnosis and treatment may involve other medical specializations.
Melanin should not be confused with another substance, melatonin, involved in regulating sleep-wake rhythm.
Does it have a relationship with eye color?
The colored part of the eye is called the iris and consists of a membrane located around the pupil. The muscles of the iris relax and contract causing the pupil to dilate and close.
When the sun’s rays hit the iris, the melanin it contains stimulates the contraction of the muscles and the narrowing of the pupil. This allows you to regulate the amount of UV rays reaching the retina and protects the latter from potentially irreversible damage.
The color of the iris depends on how much pigment it contains: if it contains little, the eyes are blue. If it contains a greater amount, they are green and if melanin is abundant, they are brown. If the melanin is unevenly distributed on the surface of the iris, the eyes appear mottled: typical of the case of brown eyes mottled with green.
Why do some people have two different colored eyes? Because the amount of melanin in their eyes is different (ocular heterochromia). Several famous people are also remembered for this characteristic. Among the most recent, rock star David Bowie; among those of the past, Alexander the Great (“…he weeps with black eyes like death; he weeps with eyes as blue as the sky…”, narrates Pascoli in the poem Alexandros).
Similarly, melanin plays a role in determining hair color. Graying, i.e. the process following which the hair turns white, is due to the aging of the melanocytes contained in the hair follicle.
Relationship between melanin and tanning
Solar radiation is mainly composed of ultraviolet rays (UVA and UVB) and infrared rays (IR): the former are responsible for tanning, the latter for the increase in skin temperature.
How is melanin produced? When we lie down in the sun, it is the UV rays themselves that activate their synthesis. In the skin, thanks to the action of some enzymes, its precursor (the amino acid tyrosine) undergoes a series of reactions which transform it into pigment.
Melanogenesis takes place in melanocytes, cells present in the deep layers of the skin and, in particular, in melanosomes, which are vesicles in which melanin accumulates.
As it is synthesized, the mature melanosomes are expelled from the melanocytes and transported towards the keratinocytes, cells found in the more superficial layers of the skin. Once they enter these cells, the vesicles open and let out the melanin, which is distributed throughout the cytoplasm. The result is the coloring of the skin surface, i.e. the tan.
It is clear that this process is not instantaneous, but takes time: this is why the skin does not turn amber immediately, but takes a couple of days to color. The effect that we perceive immediately, however, is due to the oxidation of the melanin reserves already present in the skin.
The immediate effect has protective functions but very limited in time: after 20 minutes of exposure it is already practically zero.
If you are interested in the topic, find out your phototype and how to protect yourself from the sun’s rays.
What is melanin used for?
The function of melanin is to protect the skin from the negative effects of the sun’s ultraviolet rays. By coloring the most superficial layers of the skin, this pigment creates a sort of filter that prevents (or reduces) the entry of solar radiation towards the lower layers, where it can cause serious and permanent damage.
This allows, for example, to prevent (within certain limits) inflammation of the skin, with the consequent release of oxidizing substances which trigger the formation of free radicals, the main causes of skin aging (photoaging). But in the long run, also to prevent the risk of skin cancers, from basalioma (a less serious and invasive form) to melanoma (an extremely aggressive neoplasm).
In the eyes, the melanin in the iris allows the sun’s rays to be perceived and consequently activate the muscles that constrict the pupil: in this way, the amount of light that reaches the retina is reduced, to protect it from injuries that can irreversibly compromise the view.
Types of melanin
The color of the skin, hair and eyes does not depend so much on the number of cells that produce melanin, which is more or less the same for all, but on how much they produce. Basically, it depends on the number and size of melanosomes, the vesicles in which it accumulates, and their distribution in the keratinocytes.
Melanosomes are fewer and smaller in white people than in black people.
The color also depends on the type of melanin. The main types are:
- Eumelanin: it has a blond, brown or dark brown colour.
- Pheomelanin: it has a reddish color and for this reason it is also called red melanin.
- Trichochrome: is a derivative of pheomelanin.
- Neuromelanin: is the dark pigment present in some types of neurons that form an anatomical structure of the brain called the substantia nigra.
- Allomelanins: these are natural melanins that do not have animal origin, but are present in plant species (humic acids), fungi (Aspergillus niger) or in some types of soils and coals.
There is also a distinction between immediate pigmentation, which is the one that forms directly after a few minutes of exposure, and progressive, indirect pigmentation.
The first is generated by UVA rays and depends on the oxidation of the melanin already present in the skin, a sort of emergency reserve in case of sudden sunbathing. Immediate protection is defined as ephemeral, because it is sufficient to protect only the first 20 minutes of exposure.
Indirect pigmentation, on the other hand, occurs in the following 2-3 days and is due to the fact that, following the action of UV rays, the number of melanosomes increases and the synthesis of melanin and its transport towards the more superficial layers of the skin are faster.
Synthesis and production
Melanin is synthesized in the skin from tyrosine through the action of some enzymes. Tyrosine is a non-essential amino acid, which our body produces from the essential amino acid phenylalanine.
The synthesis of melanin takes place in melanocytes, cells present in the deep layers of the skin, which accumulate them inside special vesicles called melanosomes. The mature melanosomes migrate towards the more superficial skin layers, moving into the keratinocytes.
Here they arrange themselves around their nuclei, in order to protect their DNS from the sun’s rays and prevent the formation of mutations that can give rise to tumours. When the vesicles are opened, the melanin is released, spreads and colors the skin a darker tone: this is what we call a tan.
Tanning is a natural filter that shields the entry of ultraviolet rays into the deep layers of the skin, where the induced damage could be serious.
When does the tan go away? The tan disappears because the melanin is subject to degradation and because the progressive and continuous desquamation of the superficial layers of the skin leads to a continuous loss and regeneration of new keratinocytes.
Melanin and tan
As anticipated in the previous paragraphs,…