Editor's note from Insider Pick's guides reporter Owen Burke:
While zinc oxide and titanium dioxide have been researched, tested, and mostly endorsed as reasonably safe sunscreen ingredients for many decades, the jury is still largely out on the active organic compounds used in chemical sunscreens, which are considerably younger.
Although mineral-based sunscreens are preferable because they have been tested extensively and deemed largely safe for people and the environment, they are not entirely free from controversy, either.
Zinc oxide and titanium dioxide are powders that can be manufactured as ultra-fine nanoparticles (measured in nanometers, or billionths of a meter), which allow these thick sunscreens to go on sheerly without leaving a white residue, and appear to be harming reefs, too. Plus, as with most powders, they're also potential respiratory toxins in high enough concentrations.
NPR reported in 2015 on a study published in the journal "Archives of Environmental Contamination and Toxicology," which estimated that some 6,000-14,000 tons of sunscreen end up lathering coral reefs worldwide every year. This past year, forensic ecotoxiclogist Craig Downs, Ph.D., told Vogue to look for products with "non-nano" ingredients larger than 150 nanometers, at which size their toxicity level to sea creatures — and you, as a respiratory threat in spray-ons — becomes minute.
Navigating the retail market with this information can be tricky. Terms that suggest environmental and social responsibility like "reef-safe" and "non-nano" are largely, if not entirely unregulated, so take them with a grain of salt, and do your best to find brands that support these claims. We will, too.