- Skin Colour
- Skin type
- Sun exposure and skin changes
- Sun Exposure and cancer risk
- Skin colour is primarily determined by genetic inheritance but exposure to sunlight also alters skin colour.
- There are six skin types, fair skin that always burn, dark skin that never burns and everything in between.
- Melanin is the pigment that determines skin colour as well as hair and eye colour.
- Melanin is produced by skin cells when they are exposed to the sun. The more sun exposure, the more melanin is produced.
- There are two types of melanin, eumelanin which gives skin a brown colour (tan) and pheomelanin which gives skin a red colour (burn).
- Regular sun exposure (e.g. every day) is associated with tanning. It increases eumelanin levels which gives skin a brownish tan and provides protection against the sun’s rays. This reduces the risk of burning and skin cancer with future sun exposure.
- Irregular sun exposure (e.g. only during holidays or weekends) is associated with burning. It increases pheomelanin levels and increases cancer risk.
- Exposure to artificial ultra-violet radiation from tanning beds has the same effect on skin colour and cancer risk as exposure to the sun’s ultra violet rays.
Human skin comes in a wide variety of colours, ranging from shades of dark brown to almost white. Although an individual’s skin colour 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 colour.
Levels of melanin are primarily determined by genetics; individuals born to fair skinned parents will inherit their parent’s fair skin, as individuals born to dark skinned parents will inherit dark skin. The level of inherited skin pigmentation is referred to 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 the cells which produce melanin, also influence skin colour. These factors inherited at birth, which cannot be changed, are referred to as intrinsic factors.
Extrinsic factors, things outside the body, also influence skin colour 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 the 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 skin’s upper layers. Pigmentation which occurs several days after sun exposure is a result of new melanin being produced in response to UVB exposure. Other extrinsic factors which influence skin pigmentation and colour include DNA damage (often induced by UVB exposure) and age, as the way the body produces melanin changes as a person ages.
Skin type is a classification based on the skin’s reaction to exposure to the sun’s UV radiation, after a period of non-exposure (e.g. sun exposure at the beginning of summer, when the skin has not been exposed during winter). The skin’s reaction is measured in terms of burning and tanning.
The Fitzpatrick system of classifying skin type is most commonly used in the assessment of skin cancer risk. The Fitzpatrick 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 burns, always tans.|
|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 is a pigment found in skin cells. There are two types of melanin which have visibly different effects on skin pigmentation. Eumelanin produces dark brown pigmentation and is the primary melanin type in individuals with darkly pigmented skin. Because eumelanin is insoluble, its skin-darkening (tanning) effects last a relatively long time, compared to the temporary skin-reddening effect of pheomelanin which is soluble. Pheomelanin is a red-yellow coloured pigment and the primary type of melanin in fair skinned individuals who are prone to sunburn. Eumelanin offers better protection from the sun’s UV rays compared to pheomelanin.
The melanin content of an individual’s skin is primarily determined by genetics meaning that babies inherit their skin colour from their parents. In particular a gene called plays a major role in determining an individual’s skin pigmentation.
Melanin levels are also determined by behaviours which influence exposure to the sun, because the body produces more melanin when it is exposed to the sun. An individual who works outside in the sun everyday will develop more darkly pigmented or tanned skin over time than they would if they worked indoors all day.
Melanin plays a vital role in protecting the body from UV radiation because it filters sunlight before it can damage skin cells. Sun exposure stimulates the body to produce more melanin to protect its skin cells. Thus there is a close association between skin colour and an individual’s place of origin (or their ancestor’s place of origin). Individuals with darker skin originate from areas with high levels of ultraviolet radiation, close to the equator.
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Melanogenesis is the process through which cells called melanocytes produce melanin. These cells develop in the neural tube of the foetus, then migrate to the underlying layer of the skin (the basal layer) before birth. Melanocytes also migrate to hair follicles and determine an individual’s hair colour. The process of melanin production 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 skin’s layers until it is required for photo-protection (protecting the skin from UV radiation).
In dark skinned individuals melanin is distributed throughout all the skin’s layers. It is stored for longer periods of time. In lighter skinned individuals melanin degradation occurs more quickly. The melanin which is produced is stored mainly in the upper layer of skin (the squamous cells) with very little melanin stored in the under layer of skin (the basal layer).
In determining skin colour, the number melanocytes of 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. Hyper-pigmentation (e.g. as in darkening of the nipples during pregnancy) and hypo-pigmentation (as in albinism) occur without change in the number of melanocytes.
It is the process of melanin production and the manner in which melanosomes are transferred to and distributed within keratinocytes which changes skin colour. The size and quantity of melanosomes, also determines skin colour. Darkly pigmented skin is associated with larger and more prolific melanosomes. They are elongated and the melanin they produce is stored in the keratinocytes for longer than it is stored in the keratinocytes of fair skinned individuals.
In addition to melanin, other pigments including haemoglobin and carotene also help determine skin colour.
Carotene is an orange/yellow pigment found in the skin as well as in yellow and orange vegetables. Eating excessive quantities of vegetables like carrots over a long period of time can change the skin colour. However it’s a rare occurrence and won’t happen with normal fruit and vegetable intake. If you notice your palms, face or the soles of your feet take on a yellow tinge, it’s far more likely to be a result of liver problems than it is eating too many carrots.
Excess amounts of carotene can result in accumulation in the skin, concentrated in tissues containing fat, for example the skin yellowing associated with jaundice from liver dysfunction.
Other skin pigment changes
The skin may also show abnormal colours such as:
- Cyanosis: Blueness of the skin in this condition occurs due to low levels of oxygen in the circulating blood. This deficiency causes the haemoglobin to turn reddish-violet.
- Erythema: refers to skin reddening and occurs due to increased blood flow in dilated blood vessels.
- Pallor: Loss of colour due to decreased blood flow.
Sun exposure and skin changes
Exposure to the ultraviolet radiation from the sun causes changes to the skin colour. In the short term too much sun can result in what doctors called erythema and most people refer to as 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 causing skin reddening to change to darker, tanned skin within a few days. Other UV induced skin changes include thickening of the outer layer of skin, freckles and moles and premature skin ageing, characterised by reduced elasticity, increased dryness and wrinkles.
Immediate skin changes (immediate pigmentation), seen within 5-10 minutes of sun exposure and lasting for minutes to several days, are induced by UVA radiation. They occur not because of increased melanin production but due to redistribution of melanin stored in keratinocytes in the upper layers of the skin. Delayed pigmentation which occurs several days after exposure to sunlight and has a longer duration (several weeks) is induced mainly by UVB radiation. These changes occur due to increasing production of melanin, particularly eumelanin.
Over long periods of time, chronic sun exposure increases melanin levels and increased levels of eumelanin offer additional protection from the sun’s UV radiation.
Sun exposure and cancer risk
Exposure to UV radiation from the sun and artificial sources like tanning beds is a major risk factor for all types of skin cancer (melanoma, the rarest but most deadly type, basal cell carcinoma and squamous cell carcinoma). The duration and intensity of sun exposure influences the type of skin cancer. Chronic sun exposure, for example being exposed to the sun everyday due to outdoor work, influences the melanin content of the skin; over time skin darkens. Chronic sun exposure does not appear to increase, and may offer protection from melanoma.
Intermittent, acute sun exposure is the major risk factor for melanoma, because over-exposure to sunlight causes cancerous DNA changes. Acute sun exposure refers to exposure for short periods of time in an individual whose skin is not usually exposed to the sun and is more likely to result in sunburn. This type of sun exposure occurs in office workers who spend a weekend or holiday at the beach.
Skin type influences the risk of cancer. Darker skin with more melanin is less likely to burn and skin cancer is rarely seen in darkly pigmented individuals, except on the non-pigmented skin of their bodies like the soles of their feet and palms of their hands. Fair skinned patients are more susceptible to the acute effects of sun exposure and have a relatively high risk of skin cancer.
As skin cancer risk increases with cumulative lifetime exposure to UV radiation, age is also a risk factor. Skin cancer is not however limited to the adult population; 6% of all cancers in children are melanoma, which is the second most common form of cancer in 15-29 year olds.
|For more information about Skin Cancer, including types and treatments, visit Skin Cancer Overview.|
|Learn more about Malignant skin melanoma.|
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