Sunscreen may lead to more time in the sun
A Norwegian cohort study (19) of women over the age of 40 used Cox regression to investigate the association between use of sunscreen and risk of malignant melanoma. In a model that included hair colour, freckles, UV radiation in region of residence, and the results of follow-up questionnaires, there was no significant difference between those who used high SPF sunscreen and those who used no sunscreen at all. The authors' explanation was that the latter group comprised participants who were less exposed to UV radiation.
We simply do not know whether sunscreen can increase or decrease the incidence and mortality of malignant melanoma
Some previous analyses have found a positive association between malignant melanoma and the use of sun-protection creams, i.e. that the use of sunscreen increases the risk of malignant melanoma, but recent meta-analyses find no such association (20, 21). We simply do not know whether sunscreen can increase or decrease the incidence and mortality of malignant melanoma. It is hard to imagine that sunscreen per se can cause malignant melanoma, but if people use sunscreen to enable them to stay in the sun longer rather than to reduce their UV exposure, that could explain the previous findings. In a French randomised double-blind placebo-controlled trial, one group of participants was given SPF 30 and another SPF 10. There proved to be no difference between the two groups in the number of cases of sunburn, but those who received SPF 30 sunbathed far longer than those who received SPF 10 (22).
Questions have been raised about whether sunscreen may be harmful. In the Norwegian Consumer Council's sunscreen test in 2017, 37 of the 45 sunscreens tested were found to be either environmentally damaging, allergenic or to cause hormone imbalances (23).