UV radiation from the Sun can benefit health, generating vitamin D production in the skin. The required amount of radiation is, however, quite small. In summer, an exposure of 15 minutes to the hands and face is adequate. Vitamin D is also found in food. A normal diet will provide enough vitamin D for people even in winter. In the treatment of some skin diseases such as psoriasis, UV radiation is being effectively exploited. Under a doctor's control, the benefit from the treatment is much greater than any consequential increase in skin cancer risk.
However, over exposure to UV radiation can impair the body's ability to fight off disease, in addition to causing cancer and a range of eye disorders. UV suppresses the immune system, irrespective of skin colour, making it easier for tumours to take hold and spread.
UV radiation suppresses allergic reactions of the skin and affects the immune system. When skin has been over-exposed to UV radiation, the activity of antibody-producing white blood cells is suppressed. These effects are not restricted to the part of skin actually subject to exposure, but may also occur on shielded parts of skin and throughout the whole immune system. As a result, the body fails to produce the antigens required for defence against a variety of diseases. This could have serious consequences, including a much-diminished effectiveness of vaccinations.
At the present time, the significance of a weakening of the immune system caused by UV radiation is not properly understood. The weakening can possibly act to promote the development of skin cancers and worsen infectious diseases stemming from bacteria, viruses and tropical parasites. It may also activate viruses already present on the skin, such as herpes, and lead to an increase in diseases like measles, malaria, tuberculosis, leprosy and fungal infections, all of which have a stage involving the skin. People carrying the herpes virus should protect their faces against strong sunlight.
Scientific research suggests that sunburn can alter the distribution and function of disease-fighting white blood cells in humans for up to 24 hours after exposure to the Sun. In addition, repeated exposure to UV radiation may cause more long-lasting damage to the body's immune system. Whilst little research has been conducted on the effects of decreasing stratospheric ozone on human immunity, it is likely that continued destruction of the ozone layer will lead to further health complications, in addition to skin cancers and eye disorders, as a result of the suppression of our ability to fight off disease.