Topical sunscreens act by absorbing or scattering UV radiation and are widely available for general public use as a consumer product. Surveys carried out in the UK find that sunscreen use is regarded as the most important, and by implication the most effective, sun protection measure. But is perception borne out by reality? Sunscreens applied at the thickness tested by manufacturers need only possess an SPF of 15 to prevent sunburn even for all day exposure in tropical sunshine. Yet behavioural studies show that high SPF (>15) sunscreens do not always prevent sunburn. That the protection achieved is often less than that expected depends upon a number of factors: application thickness and technique; type of sunscreen applied; resistance to water immersion and sand abrasion; and when, where and how often sunscreen is re-applied. These factors provide ample evidence that the numerical measure of protection indicated on the product pack is generally higher than achieved in practice. This mismatch between expectation and realisation may be one contributing factor why sunscreens have been reported to be a risk factor in melanoma.