Sun protection can start with simple habits: seek shade when the sun is strong, wear a broad-brimmed hat and covering clothes, and plan outdoor time around heat and ultraviolet exposure. Sunscreen can cover skin that clothing does not. The old version of this page reproduced a newspaper story about SPF labels without linking readers to the original research.
What does the randomized evidence say?
The Nambour trial assigned 1,621 Australian adults to daily sunscreen use or discretionary use, alongside a separate beta-carotene comparison. Over about four and a half years, daily sunscreen did not significantly lower the number of people with a first new basal-cell or squamous-cell cancer. It did reduce the total number of squamous-cell tumors. Beta-carotene did not prevent either type in that trial (the original Nambour randomized trial). These distinct outcomes should not be collapsed into a claim that sunscreen prevents every skin cancer.
Researchers followed the participants further and recorded 11 new primary melanomas in the daily-use group versus 22 in the discretionary group. The estimate for all melanomas narrowly missed the usual statistical threshold, while the analysis of invasive melanomas suggested a reduction. The authors described melanoma prevention as possible, not certain (Nambour melanoma follow-up).
A useful daily routine
Shade and clothing reduce the amount of skin exposed and do not require choosing a particular ingredient. Add a broad-spectrum sunscreen to exposed skin when needed, and reapply according to its label, especially after swimming or sweating. SPF is a laboratory measure of protection from sunburn under specified conditions; it is not permission to stay in strong sun indefinitely. A vitamin supplement cannot replace these habits. The aim is to prevent burning and repeated excess exposure while still enjoying time outdoors.
