What sunscreen ingredient is known to cause coral bleaching?

The sunscreen ingredient known to cause coral bleaching is oxybenzone.

Oxybenzone, also called benzophenone-3 or BP-3, is an organic ultraviolet filter used in some sunscreen formulations. It absorbs ultraviolet radiation, including portions of the UVA and UVB ranges, helping protect skin from sun exposure. The compound can wash from swimmers’ skin into coastal water, where laboratory studies have linked sufficiently high concentrations with harm to coral larvae, DNA damage, deformities, and increased vulnerability to bleaching.

Oxybenzone is sometimes confused with octinoxate, another organic UV filter that has also raised coral-health concerns. Zinc oxide and titanium dioxide are mineral UV filters and are not the same chemicals. Avobenzone is another organic sunscreen filter, but it is not the canonical answer to this coral-bleaching question.

The environmental issue became especially prominent in Hawaii, which enacted legislation banning the sale of sunscreens containing oxybenzone and octinoxate; the restriction took effect in 2021. The science is more nuanced than the slogan: coral bleaching has many causes, especially unusually warm seawater, and researchers continue to debate how laboratory concentrations compare with real-world exposure. Oxybenzone remains a well-established quiz answer because of its documented environmental controversy.