The purpose of sunscreen is to create a barrier against ultraviolet (UV) radiation, including UV-A and UV-B.1 Photoaging is primarily caused by exposure to UV-A, whereas sunburns are caused by UV-B. Both forms of UV cause DNA damage, with UV-A believed to cause DNA damage indirectly through the production of reactive oxygen species and UV-B more directly through the formation of pyrimidine photoproducts. More recently, data suggest that exposure to the visible light spectrum can also cause pigmentation. Exposure to both UV-A and UV-B has been demonstrated to increase the risk of nonmelanoma skin cancers — basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) — as well as melanoma.
Sunscreen contains ingredients, or UV filters, that protect against and/or counteract the DNA damage caused by UV exposure. These UV filters are categorized by their composition and are either organic (ie, “chemical”), such as oxybenzone, avobenzone, octinoxate, and octisalate; or inorganic (ie, “physical”), such as titanium dioxide and zinc oxide. Sunscreen may also be formulated with antioxidants that can further mitigate DNA damage caused by UV exposure.
The use of sunscreen, as well as sun avoidance and wearing protective clothing, are considered important strategies to help prevent the development of nonmelanoma skin cancers, melanoma, and photoaging.1 The American Academy of Dermatology recommends that individuals use a broad-spectrum sunscreen of SPF 30 or higher that is water resistant, in addition to other sun protection measures.2
The use of sunscreen reduces photodamage and DNA damage; therefore, its use should also decrease the risk of skin cancers. However, questions have been raised about sunscreen safety, including whether the UV filters used in sunscreen can actually cause cancer.
Nonmelanoma Skin Cancers
To date, there has been 1 randomized controlled trial (RCT) that has evaluated the use of sunscreen and its effect on the incidence of skin cancer. This trial was conducted in the 1990s and randomly assigned 1621 Australians to use SPF 16 sunscreen on their head, neck, arms, and hands every morning or use sunscreen at their discretion (such as not at all or only recreationally).3 During 4.5 years of study follow-up, the use of sunscreen significantly decreased the incidence of SCC (rate ratio [RR], 0.61; 95% CI, 0.46-0.81), but not BCC.
Participants were followed for an additional 8 years after that study ended, and the preventive effect against SCC persisted (RR, 0.62; 95% CI, 0.38-0.99).4 There was a nonsignificant trend toward a lower rate of BCC among individuals who used daily sunscreen.
This RCT was included with 28 observational studies in a meta-analysis, which found no association between the use of sunscreen and the development of all skin cancers (odds ratio [OR], 1.08; 95% CI, 0.91-1.28), which remained consistent when adjusted for skin phenotype.5 Similarly, there was no association between sunscreen use and the risk of nonmelanoma skin cancers (OR, 0.99; 95% CI, 0.62-1.57).