Dying For A Tan

No one knows the suns energy output although it is estimated to be 386 billion, billion megawatts. Some of this energy makes it to the Earth in the form of ultraviolet radiation. There are 3 types of ultraviolet radiation: UVA, UVB and UVC. These UV rays can damage skin cells if they come into contact with unprotected flesh, this can in turn cause skin cancer. So why would anyone want to be out in the sun for long periods of time? The simple answer is that UVA library and UVB rays can both give you a suntan. [1]

To understand the effects on the body of ultraviolet radiation we must first look at the physiology of the skin. The skin (or as it is sometimes known the cutaneous membrane) envelops surface of the body. It is considered to be an organ as it is made up of many tissues all working together. The composition of the skin consists of two main parts. The exterior, thinner layer, which is made up of epithelial tissue, is the epidermis. [2] The epithelial tissue is composed of stratified squamous epithelium and has no fixed thickness. The epidermis, depending on where it is located on the body, consists of 4 or 5 layers. With 3 or 4 of these layers respectively being made up of dead cells. [3] Below the epidermis is the dermis, which is made up of connective tissue and elastic fibres. There are only a few cells present in the dermis including fibroblasts and macrophages. Also present in the dermis are two of the three major pigments, which determine our skin colour. The first is a yellowy-orange substance called carotene. Carotene is found in the fatty areas of the dermis and is the precursor of vitamin A. The other pigment isn't directly found in the dermis but is found in the blood vessels running through dermis. This pigment is called Haemoglobin. Haemoglobin will only have a major impact on the skins pigmentation if there is little carotene and melanin. Haemoglobin gives the skin its pinkish tones. The final pigmentation is melanin and this dark pigment, is primarily involved in giving people a tan. [2] Melanin is manufactured in skin cells called melanocytes located in the stratum basale region of the epidermis. When we come into contact with Ultraviolet radiation, from the sun or a sun lamp for example, the melanocytes are stimulated. They begin to produce new melanin granules. The new melanin granules are transferred to upper epithelial tissue of the skin. The pigment keeps on building up until there is sufficient protection from the UV radiation. The result of which is darker skin and thus a tan. [4]

Nearly every human being has the same number of melanocytes. The amount of melanin produced and the degree of granular aggregation will decide a persons skin colour. [3] However not everything always works out so well, and pigmentary diseases are common. Pigment loss may be from all over the body or just certain parts. "Patchy loss" as it is sometimes called, can be seen in the most common pigmentation disease, Vitiligo. Vitiligo affects 1% of the population and is not any more common in any one particular race. Vitiligo is the partial or total disappearance of melanocytes from patches of skin producing white non-scaly macules. The disappearance of the melanocytes maybe due to an autoimmune response within the body, where antibodies actually attack and destroy the melanocytes. [2] Just under a third of patients can site a family history of the disorder. Vitiligo is very infrequently present at childbirth and often appears when a person is 10- 30 years old and maybe agitated by injury or sunburn. The disease is very unpredictable and can spread, remain fixed or (in a limited number of cases) repigmate the diseased skin. In light skinned people the disease is often only seen when the affected areas become sunburnt, however in dark skinned people the disease is seen all year. So avoidance or protection from the sun is prerequisite. Another less common, but probably more well-known pigmentation disease is Albinism. Albinos have normal melanocytes numbers, but cannot produce any melanosome because of a faulty gene control of tyrosinase. [5] Therefore melanin will be missing from the skin, hair and eyes. [2] Due to this, none of the skin should come into contact with the ultraviolet radiation at all! The usual protection (sunscreens, opaque clothing etc) is essential whenever an albino person wishes to go out in the sun, as due to the complete lack of melanin they will have no natural protection from the sun. Both Vitiligo and Albinism are examples of Hypopigmentation. There is another form of pigmentary diseases however these are much less severe and often disappear after a while. Freckles and Chloasma are both examples of Hyperpigmentation. Both these diseases are due to Hypermelanosis and require no special treatment and will recover fully in time. [5]

Of course it is not only people with pigmentation diseases that need to be careful when they are out in the sun. Everybody has different skin, although most people can be classified as having a certain skin phototype (SPTs). SPT's are usually genetically determined although as a patients get older it can also depend on how the individual patient reacts in the sun and his or hers history of sun exposure. Table 1 summarises how skin phototypes are categorised: [6]

Table 1: Skin Phototypes.

Phototype Reactions to Sun Comments

1 Burns Easily; Never Tans Comprises, with SPT 2, 25% of light skinned people in the United States.

2 Burns Easily; tans minimally Comprises, with SPT 1, 25% of light skinned people in the United States.

3 Burns moderately; tans gradually

4 Burns minimally; tans always

5 Burns rarely; tans profusely Comprises people with brown skin; can sunburn following long exposures to UVR

6 Never burns; deeply pigmented Comprises people with black skin; can sunburn following long exposures to UVR

E.J.Barone. J.C.Jones. J.E.Schaefer. Skin Disorders. 2000. 1st edition.123.

Of course even having an SPT of 5 or 6 does not guarantee that you will not sunburn from UVA, UVB or UVC rays. UVC rays have a wavelength of less than 280 nm and never reaches the earth as it is currently fully blocked by the ozone layer. UVB (280-320) and UVA (320 - 400 nm) do make it to the earth's surface. [7] UVB radiation is mostly absorbed by the epidermis [5] and solar erythema or sunburn will tend to develop between 12 and 24h after sun exposure. Damaged Keratinocytes release prostaglandins and related mediators and this is why the sunburn and erythema appear. However, tanning may happen 48-72h

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