The concept of the sun protection factor was originally proposed by the Austrian scientist Franz Greiter and subsequently adopted by many regulatory authorities and the cosmetic and pharmaceutical industries. It is popularly interpreted as how much longer skin covered with sunscreen takes to burn compared with unprotected skin.1 This interpretation can encourage users to prolong their sun exposure accordingly, yet there is ample evidence that the numerical measure of protection indicated on the product pack is generally higher than achieved in practice.2 This mismatch between expectation and realisation may be one contributing factor to why use of sunscreens has been reported to be a risk factor in melanoma.3 I suggest that the role of sunscreens as a preventive measure against sunburn, and presumably skin cancer, would be strengthened if a qualitative rather than quantitative measure of photoprotection was used.