Sun and skin – a dangerous combination
Box 2 | Types of skin cancer
There are only three cell types in the skin that can become cancerous as a result of exposure to ultraviolet radiation: basal cells, squamous cells and melanocytes. All three occur in the epidermis – the upper layer of the skin.
- Basal cell carcinomas account for about 80 per cent of all skin cancer cases. At first they look like small, pinkish raised areas. They are most common on areas that receive the greatest exposure to ultraviolet radiation – the face, ears and neck. They are not painful, but they grow and eventually start to look like an ulcer, because they develop a crater in the middle. However, they don’t spread into the rest of the body and so are not usually lethal. If left in place they can end up looking very unsightly but they are easy to remove.
- Squamous cell carcinomas account for about 10 to 20 per cent of skin cancers. These are more dangerous than basal cell carcinomas. They grow faster and can spread beyond the skin and kill. They typically appear on the face, ears, the top of a bald head and also on hands and arms. They are more common in men than women. They look like sores, sometimes oozing fluid or even blood and often with crusts on them. They may feel tender. They can grow quite fast – especially those on the lip and ear.
- Melanocytes are the melanin-producing cells and they are scattered along the bottom of the epidermis. Every basal cell is attached to a melanocyte. There is one melanocyte per 10 to 20 basal cells. (Melanocytes also lie in the hair roots, where they give their pigment to the hair, thereby determining its colour.) Melanin produced in the melanocytes is delivered to the basal skin cells.
Paler-skinned people do not have fewer melanocytes than black people, but simply produce less melanin and a different kind of melanin per melanocyte. Ultraviolet radiation stimulates the enzyme that makes melanin.
Melanomas are the deadliest skin cancers of all. They account for only about 5 per cent of cases but cause 80 per cent of skin cancer deaths. Melanomas can occur anywhere on the body. The important signs are either a new mole, a recent change in the size, shape or colour of an existing freckle or mole, or bleeding or tenderness of a mole. As it grows, a melanoma will eventually push beyond the epidermis of the skin, and then can spread throughout the body. But if spotted early, it can be easily removed before it spreads, and the prognosis is then good. If left untreated, a malignant melanoma is usually fatal.
Melanomas may occur on areas of the body that don’t receive regular exposure to the sun. It is thought that they are caused by brief intense exposure to ultraviolet radiation for short periods – especially during childhood or adolescence. People most at risk seem to be those in indoor occupations as adults, with little time in the sun, who spend a short time each year exposed to the sun and get sunburnt. They recover after their holiday but may develop a melanoma 20 or more years later.
The bad news
Australia – particularly the northern parts – is the world’s skin cancer capital. Statistically speaking, an Australian has a far greater risk than almost anyone else of developing one of the non-melanoma cancers at some stage in life. Skin cancer is the most common cause of cancer death in white people aged 25 to 40 in Australia.
Boxes
Box 1. The ultraviolet family
Box 3. The molecular mechanisms of skin cancer
Box 4. Diagnosing skin cancer
Box 5. Australian research
Box 6. Sunblocks and sunscreens
Related sites
Melanoma (Queensland Institute of Medical Research, Australia)
Non-melanoma skin cancer (Australian Institute of Health and Welfare)
Page updated November 2008.