Overall there is some very limited evidence from studies done in Australia (where the frequency of skin cancer in fair skinned people is very high) that sunscreens might help protect against the risk of skin cancer. But this is not conclusive and the best advice for people in the UK is to use sunscreens as part of an overall programme of skin protection. Other sensible measures to take - such as avoiding prolonged exposure to strong sunlight and wearing a hat and appropriate protective clothing if going out at the hottest times of day - certainly sunscreens shouldn't be used to allow excessive sunbathing.

Skin cancer is becoming increasingly common in the UK with more than 40,000 new cases being diagnosed a year.
There are three main types of skin cancer: rodent ulcers (also called basal cell carcinomas or BCCs), malignant melanomas and squamous cell carcinomas (SCCs). Rodent ulcers are by far the commonest of the three.

Excessive exposure to sunlight is a risk factor for the development of all types of skin cancer but the pattern is slightly different. For melanomas, excess exposure to sun as a child, especially if this caused sunburns, increases the chances of the growth developing in adult life. For both BCCs and melanomas intermittent, intensive, exposure, again especially if there is burning, increases the risk. For SCCs, however, it seems that long term, more or less continuous exposure to the elements (for example people with outdoor jobs, like farmers) seems more important. Being fair skinned and/or having light coloured or red hair also increases the chances of getting skin cancer.

Although there is no doubt that the ultraviolet radiation in sunlight is a cause of skin cancer, there must be other factors involved, which are not yet properly understood. Skin tumours do sometimes develop in people who have had very little exposure, and some occur on parts of the body which are usually covered.

Ultraviolet radiation in sunlight is made up of two types: UVA and UVB. The older types of sunscreens, which were intended simply to prevent sunburn, only protected against UVB. Today's sunscreens protect against both types of radiation and come in varying 'strengths'. Protection against UVB is measured by a sun protection factor (SPF) and this needs to be at least 15 to offer useful protection. Protection against UVA is measured by a rating system using one to four stars. The higher the number of stars, the better the level of protection. Theoretically, if you use a SPF15 sunscreen properly, your risk would be a fifteenth of the normal risk (around 7% of normal), but in practice, because we rarely use them properly, we probably only gain a 20 / 50 % reduction of the normal risk.

Sunscreens have few side effects although some people find they cause stinging or skin irritation. Their main danger is that people might feel they give false security and spend longer in strong sunlight than they should do because they are using a sunscreen, thereby increasing their skin cancer risk.