The most well known effect of UV radiation is the slight reddening or burning of the skin in sunshine. This change of colour is caused by an expansion of the skin's blood vessels. For most people burning is followed by tanning within a couple of days. A permanent tan will occur when the UV radiation causes a pigment called melanin to form in the pigment cells of the skin. Over a period of years, exposure to radiation originating from the Sun causes damage in the skin's connective tissues, so-called photo-aging. This shows itself as a thickening of the skin, as wrinkles and decreasing elasticity. UV radiation increases the risk of getting skin cancer.
Research has shown that even small amounts of UV radiation can cause considerable harm. UV damages the genetic material of DNA and is related to some types of skin cancer. It is important to note however, that UV radiation has always had this effect on humans. In recent years non-melanoma skin cancer has become more prevalent in many parts of the world because people are spending more time in the Sun and are exposing more of their skin in the process.
The relationship between the occurrence of milder non-melanoma skin cancers and time spent in the Sun is well documented. Such cancers generally occur in people in their 70s and 80s on areas of the skin usually exposed to sunlight (such as the face or hands). Malignant melanoma however, usually occurs in younger people and in skin areas not necessarily exposed to sunlight. It tends to occur most commonly among groups of people less likely to have spent significant amounts of time outdoors.
The risk of developing malignant melanoma is directly related to the sensitivity of an individual's skin to the Sun. Fair-skinned individuals are more susceptible than darker-skinned individuals. The victims are almost exclusively Caucasians, particularly fair-skinned Caucasians. The incidence of malignant melanoma has been increasing among light-skinned populations around the world for decades.
Ozone in the stratosphere protects Earth from damaging amounts of UV radiation. A depleted ozone layer would allow more of the Sun's rays to reach Earth's surface. An increase in the levels of UV reaching the Earth as a result of ozone depletion may compound the effects of spending more time in the Sun. According to some estimates a sustained 10% global loss of ozone may lead to a 26% increase in the incidence of skin cancers among fair skinned people.
Australia, with high sunshine levels, has very high skin cancer rates. An estimated 2 out of every 3 people in most parts of the country will develop some form of skin cancer. In Queensland, where sunshine levels are greatest, the probability jumps to 3 in every 4. In 1930s America the chances of developing the more serious malignant melanoma was 1 in 1500. In 1991 it had soared to 1 in 150, and it is predicted to rise to as much as 1 in 75 early in the 21st century.