With peak UV reaching very high levels this week, a good sunscreen is a Phoenician's best friend.
But is that friendship toxic to humans, animals or the environment?
A new report by the National Academies of Sciences, Engineering and Medicine joins a chorus of experts who have long called for better answers.
The paper calls for the EPA to perform environmental risk assessments of the active ingredients in sunscreens.
When used regularly, broad-spectrum sunscreens of SPF 30 and above reduce risks of skin cancer, sunburn and premature aging.
But some of their UV-filtering ingredients persist and build up in ecosystems, and much more research is needed to assess their damage, and how their impacts vary by species, water flow and proximity to human activity.
The paper says such studies should account for climate change, rising ocean temperature and pollution, and test what happens when UV filters mix.
