Index
Human skin comes in a wide variety of colors, from shades of dark brown to almost white.
Although the color of an individual’s skin is influenced by numerous factors, the most significant is its content of a pigment called melanin .
Melanin is also the pigment responsible for determining hair and eye color.
Melanin levels are determined primarily by genetics; People born to light-skinned parents will inherit light skin from their parents, just as people born to dark-skinned parents will inherit dark skin.
The level of inherited skin pigmentation is known as constitutive pigmentation.
A number of other factors determined at birth – for example, the way a person’s body produces hormones and the way these hormones signal cells that make melanin – also influence skin color.
These factors inherited at birth, which cannot be changed, are known as intrinsic factors.
Extrinsic factors, things outside the body, also influence skin color and provide acquired pigmentation. Exposure to ultraviolet (UV) radiation from the sun is the most important extrinsic factor.
The sun emits UVA and UVB rays, and different types of UV rays have different effects on skin pigmentation.
Exposure to UVA rays produces immediate pigmentation by influencing melanin, which has already been produced and is waiting in the upper layers of the skin.
Pigmentation that occurs several days after sun exposure is the result of the production of new melanin in response to UVB exposure.
Other extrinsic factors that influence skin pigmentation and color include DNA damage (often induced by UV exposure) and age, as the way the body produces melanin changes as that a person grows old.
Type of skin
Skin type is a classification based on the skin’s reaction to exposure to UV radiation from the sun, after a period of no exposure (eg, sun exposure in early summer, when the skin has not been exposed during winter).
Skin reaction is measured in terms of burning and tanning.
The Fitzpatrick skin type classification system is most commonly used in skin cancer risk assessment.
Fitzpatrick’s skin types are:
- Type I: extremely fair skin, always burns, never tans.
- Type II: Fair skin, always burns, sometimes tans.
- Type III: medium skin, sometimes burning, always tanned.
- Type IV: olive skin, rarely burns, always tans.
- Type V: moderately pigmented brown skin, never burns, always tans.
- Type VI: markedly pigmented black skin, never burns, always tans.
melanin
Melanin is a pigment found in skin cells. There are two types of melanin that have visibly different effects on skin pigmentation.
Eumelanin produces dark brown pigmentation and is the main type of melanin in individuals with dark pigmented skin.
Because eumelanin is insoluble, its skin darkening (tanning) effects last for a relatively long time, compared to the temporary skin reddening effect of pheomelanin which is soluble.
Pheomelanin is a red-yellow pigment and the main type of melanin in fair-skinned people who are prone to sunburn. Eumelanin offers better protection against UV rays from the sun compared to pheomelanin.
The melanin content of an individual’s skin is determined primarily by genetics, which means that babies inherit skin color from their parents.
In particular, a so-called gene plays an important role in determining the pigmentation of an individual’s skin.
Melanin levels are also determined by the behaviors that influence sun exposure, because the body produces more melanin when exposed to the sun.
An individual who works outside in the sun every day will develop more pigmented or tanned skin over time than working indoors all day.
Melanin plays a vital role in protecting the body against UV radiation because it filters sunlight before it can damage skin cells. Sun exposure stimulates the body to produce more melanin to protect skin cells.
Therefore, there is a close association between skin color and the individual’s place of origin (or the place of origin of his ancestor). Individuals with darker skin originate in areas with high levels of ultraviolet radiation, near the equator.
Melanogenia
Melanogenesis is the process through which cells called melanocytes produce melanin. These cells develop in the neural tube of the fetus and then migrate to the underlying layer of skin (the basal layer) before birth.
Melanocytes also migrate to hair follicles and determine the color of an individual’s hair. The melanin production process is influenced by hormones, immune and inflammatory factors, and brain signals.
Melanocytes interact with other skin cells called keratinocytes, which are responsible for storing melanin in cells called melanosomes.
Each melanocyte interacts with 30-40 keratinocytes to which it transfers melanin for storage in the layers of the skin until it is required for photoprotection (protecting the skin from UV radiation).
In dark-skinned individuals, melanin is distributed throughout all layers of the skin. It is stored for long periods of time. In lighter-skinned individuals, the degradation of melanin occurs more rapidly.
The melanin produced is mainly stored in the upper layer of the skin (the squamous cells) with very little melanin stored in the lower layer of the skin (the basal layer).
In determining skin color, the number of melanocytes is not as important as the type of melanin the cells produce. The number of melanin-producing cells is similar between people of different ethnic groups.
Hyperpigmentation (for example, as in darkening of the nipples during pregnancy) and hypopigmentation (as in albinism) occur without change in the number of melanocytes.
It is the process of melanin production and the way in which melanosomes are transferred and distributed within keratinocytes that changes the color of the skin. The size and quantity of melanosomes also determines the color of the skin.
Dark pigmented skin is associated with larger and more prolific melanosomes. They are elongated and the melanin they produce is stored in keratinocytes for longer than it is stored in keratinocytes of fair-skinned individuals.
In addition to melanin, other pigments, such as hemoglobin and carotene, also help determine skin color.
Hemoglobin
Hemoglobin is a red pigment that runs through the blood vessels. This causes the skin to become redder in places where the blood vessels are closer to the surface, for example, the lips.
Carotene
Carotene is an orange / yellow pigment found in skin, as well as yellow and orange vegetables. Eating excessive amounts of vegetables like carrots over a long period of time can change the color of the skin.
However, it is rare and will not occur with normal consumption of fruits and vegetables. If you notice a yellow tinge to your palms, face, or soles, it is much more likely due to liver problems than eating too many carrots.
Excessive amounts of carotene can lead to accumulation in the skin, concentrated in fat-containing tissues, for example, the yellow color of the skin associated with jaundice from liver dysfunction.
Other changes in skin pigment
The skin can also show abnormal colors such as:
- Cyanosis: the whiteness of the skin in this condition occurs due to low levels of oxygen in the circulating blood. This deficiency causes the hemoglobin to turn reddish-purple.
- Erythema – refers to redness of the skin and occurs due to increased blood flow in dilated blood vessels.
- Paleness: loss of color due to decreased blood flow.
Sun exposure and skin changes
Exposure to ultraviolet radiation from the sun causes changes in skin color. In the short term, too much sun can result in what doctors call erythema and most people call sunburn.
Artificial exposure to UV radiation, for example, from a tanning bed has a similar effect.
In the longer term, UV exposure stimulates melanin production, which causes the redness of the skin to change to darker, tanned skin within a few days.
Other UV-induced skin changes
- Thickening of the outer layer of the skin.
- Freckles and moles.
- Premature aging of the skin. characterized by reduced elasticity, increased dryness and wrinkles.
UVA radiation induces immediate changes in the skin (immediate pigmentation), seen within 5-10 minutes of sun exposure and lasting from minutes to several days.
They do not occur due to increased melanin production, but rather due to the redistribution of melanin stored in keratinocytes in the upper layers of the skin.
Delayed pigmentation that occurs several days after exposure to sunlight and lasts longer (several weeks) is mainly induced by UVB radiation.
These changes occur due to increased production of melanin, especially eumelanin.
Over long periods of time, chronic sun exposure increases melanin levels and elevated eumelanin levels offer additional protection against UV radiation from the sun.
Sun exposure and cancer risk
Exposure to UV radiation from the sun and man-made sources such as tanning beds is a major risk factor for all types of skin cancer (melanoma, the rarest but most deadly type, basal cell carcinoma, and carcinoma of the squamous cells).
The duration and intensity of sun exposure influences the type of skin cancer. Chronic sun exposure, for example being in the sun every day due to outdoor work, influences the melanin content of the skin; over time the skin darkens.
Chronic sun exposure does not appear to increase, and may offer protection against melanoma.
Acute, intermittent exposure to the sun is the main risk factor for melanoma, because excessive exposure to sunlight causes cancerous changes in DNA.
Acute sun exposure refers to exposure for short periods of time in a person whose skin is not usually exposed to the sun and is more likely to produce a sunburn.
This type of sun exposure occurs in office workers who spend a weekend or vacation at the beach.
Skin type influences cancer risk. Darker skin with more melanin is less likely to burn, and skin cancer is rarely seen in people with dark pigments, except on the unpigmented skin on their bodies, such as the soles of the feet and the palms of the hands. .
Fair-skinned patients are more susceptible to the acute effects of sun exposure and have a relatively high risk of skin cancer. Because the risk of skin cancer increases with cumulative lifetime exposure to UV radiation, age is also a risk factor.
However, skin cancer is not limited to the adult population; 6% of all cancers in children are melanoma, which is the second most common form of cancer between 15 and 29 years of age
