Sun and skin – a dangerous combination
Key text
This topic is sponsored by Healthpact.
With its sunny climate and predominantly pale-skinned population, Australia has one of the world’s highest rates of skin cancer. But with early detection, most skin cancers can now be cured.
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You will get more from this topic if you have mastered the basics of DNA and genes and electromagnetic radiation – these links will take you to an annotated list of sites with helpful background information. |
What is in sunlight?
The sun is an immense nuclear reactor. As well as producing heat and light, it also emits other types of electromagnetic radiation. We cannot detect much of this radiation without special instruments. This can be a problem, because sometimes the ‘hidden’ components of sunlight can damage living things.
Fortunately, the Earth’s atmosphere filters out much of the more dangerous solar radiation. But some gets through – mainly in the ultraviolet (UV) band (Box 1: The ultraviolet family).
The ultraviolet radiation in sunlight causes skin cancer
Ultraviolet radiation doesn’t get very far into our bodies. It mainly affects our skin and eyes. Even though we can’t feel it – just as we can’t feel an X-ray – it can damage us. The higher the dose, the greater the likelihood of damage.
The most serious effect of sunlight on skin is the generation of cancer. There are three main types of skin cancer, classified according to the type of skin cell affected (Box 2: Types of skin cancer). The majority of skin cancers are not lethal.
Cancer is often brought about by exposure to a mutagen, which can change (or mutate) the genes. Ultraviolet radiation is a well-known mutagen. It promotes a chemical change in the DNA, which may manifest itself as an error or misprint in the information encoded in a gene (Box 3: The molecular mechanisms of skin cancer).
A mutation can take many years to show up as a symptom. In the intervening decades, the altered DNA has remained, and the misprint in the gene has been copied into more and more cells. Two in three Australians will have been diagnosed with skin cancer before they turn 70.
Sunlight also causes other damage
Sunlight doesn’t just cause cancer. It can also cause painful sunburn, which usually shows up the day after exposure. Sunlight also ages skin. Sun-weathered skin becomes leathery and loses its softness and lustre. Other blemishes, such as moles and solar keratoses, can also form. These are unsightly but they are not usually considered dangerous.
The eyes are also affected by radiation from the sun. Minor damage will show up in the formation of a pterygium, which can be removed. Far more serious are cataracts, which can cause blindness.
Reactions to sunlight differ
People vary in how much ultraviolet exposure their bodies can tolerate before their skin is damaged or cancer occurs. Because dark-skinned people have greater amounts (and a different form) of melanin in their skin, they are much less sun-sensitive than fair-skinned people. Melanin absorbs ultraviolet radiation, like a sunblock. The cells beneath the melanin are therefore somewhat protected.
Exposure to sunlight causes the skin to produce more melanin in an attempt to protect itself. In pale-skinned races, this shows up as a tan. Dark-skinned people will also produce more melanin after time spent in sunlight.
In pale-skinned people, the maximum amount of melanin that the skin can make isn’t enough to protect against the doses of ultraviolet radiation that occur in and around the tropics. When people of European origin live in places that have much higher levels of year-round ultraviolet radiation than Europe, then their skin can never naturally protect itself. This is the problem facing most of Australia’s population.
The rate of skin cancer in Australia is very high
Australians have one of the highest rates of skin cancer in the world at nearly four times the rate in the USA. With only 0.3 per cent of the world’s population, we manage to account for 6 per cent of all the lethal forms of skin cancer diagnosed globally. About 1200 people die each year in Australia as a result of skin cancer.
The skin cancer rate is likely to increase when many of the ‘baby-boomers’ who loved the sun in their youth enter their 50s and find that cancers have developed. In addition, ozone depletion in the stratosphere is increasing the amount of ultraviolet radiation reaching the ground over Australia, thereby worsening the risk.
In future, the skin cancer rate may fall as the understanding of the link between sunlight and cancer becomes more widespread and people protect themselves more.
Detecting and dealing with skin cancer
If caught early enough, most skin cancers can be removed with very little harm done (Box 4: Diagnosing skin cancer). However, the longer a cancer remains, the greater are the chances that it will spread.
Australian research
Because of the seriousness of the skin cancer problem in Australia, our researchers are among the world leaders in the field (Box 5: Australian research) .
How to prevent skin cancer
Public education campaigns have made most Australians aware of sun damage. We rank as one of the best countries in the world in terms of how we deal with the problem. Obviously, keeping out of the sun is the best prevention. Next comes sun-proof clothing, then sunblocks and sunscreens (Box 6: Sunblocks and sunscreens). Finally, a careful check of your skin will help catch any potential cancers as early as possible.
Boxes
1. The ultraviolet family
2. Types of skin cancer
3. The molecular mechanisms of skin cancer
4. Diagnosing skin cancer
5. Australian research
6. Sunblocks and sunscreens
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Page updated March 2009.