There is no evidence you should reapply sunscreen every 2 hours.
The FDA's 2-hour reapplication guideline for sunscreen is based on weak studies and circular logic, new analysis shows.
The lesswrong investigation found that the widely repeated sunscreen reapplication rule is supported by a weak evidence base. The FDA first introduced the 2-hour recommendation in 2007, citing a 2001 study of beachgoers with a tiny sample and virtually no controls, along with press releases and pamphlets from the AAD and other authorities. Despite criticisms, the rule was carried forward in the 2011 final rule and remains on labels today, with the agency defending it by referencing those same sources.
- The FDA's 2-hour reapplication rule first appeared in a 2007 proposed rule, not in earlier guidelines dating to 1978 and 1993.
- Two studies cited by the FDA include Wright et al. 2001 (only 67 beachgoers in an uncontrolled survey) and a press release from the AAD.
- The 2011 final rule codified the 2-hour language despite criticism that data did not support the timeframe.
Why It Matters
This challenges a widely accepted public health guideline, urging consumers and regulators to demand better evidence for routine safety recommendations.