12 January 2009

Skin changes caused by UV

Suntan, sunburn and ageing - all ways in which the sun can affect your skin. But how does it all work? Get the lowdown here.


The sun's UV rays can affect the skin in the following ways:

Suntan is the result of a complex series of chemical and physical processes in the skin caused by UVA and UVB.

UVB activates the production of vitamin D by acting on a chemical present in the epidermis. UVB also activates melanin-producing cells in the epidermis causing the chemical reactions which result in the production of melanin, the suntan pigment. It also causes the melanin producers to share the pigment with neighbouring keratin producers in an attempt to protect these from sun damage.

However, the melanin producers in the skin don't have the ability to make enough melanin to protect the skin adequately.

UV light also results in the production of other cells, called keratinocytes, which carry the melanocytes to the surface of the skin. The increase in pigment provides the brown colour that we call a tan, and the increase in the number of keratinocytes makes the horny layer of the skin thicker. This gives the skin a leather-like appearance.

A true tan begins to appear 2-3 days after exposure and reaches a peak 2-3 weeks later.

A suntan is not a sign of good health. It is a defence mechanism that still permits UV light to cause ageing and other changes in the skin.

Eighty percent of sun-induced skin damage occurs before the age of 18 and manifests later in life.

Sunburn occurs when the body receives an overdose of radiation.

The UVB light in the sun’s rays burns the skin cells and breaks them down, which increases blood flow to the area and the flow of fluid into the cells. This chain reaction causes redness, swelling, pain and, in severe cases, blistering.

The cells begin to repair within 71 hours of exposure, but the repaired skin has a thicker upper layer than before.

The common harmful effects of UVA are invisible and accumulate over the years.

UVA damages the dermis, causing wrinkles and loss of elasticity, which makes the skin look "old". These changes start to appear during the early 20s in the unprotected skins of fair-skinned people.

Leucoplakia is a slightly raised pale white blotch that may occur on the outer half of the lip.

Leucoplakia that isn't due to sunlight occurs on other mucous surfaces. This is pre-cancerous and could turn into squamous cell carcinoma.

Solar keratosis
Solar keratosis refers to small, irregular, whitish-yellow or brown scaly thickening of the skin, which can be found on the neck, ears, hands and outer half of the lower lip. This is not skin cancer, but a warning that the skin is prone to cancer.

- (Cancer Association of South Africa, November 2007)


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Skin expert

Dr Suretha Kannenberg holds a degree in Medicine and a Masters in Dermatology from the University of Stellenbosch. She is employed as a consultant dermatologist by Stellenbosch University and Tygerberg Academic Hospital, where she is involved in clinical duties and the training of medical students and dermatology residents. Her areas of interest and research include vitiligo, eczema and acne. She also performs limited private practice work in the Northern suburbs of Cape Town in general and cosmetic dermatology.

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