“Natural” isn’t always best, and ironically, the same studies people use to demonize chemical filters as being unsafe to reef environments ALSO show mineral filters have similar or more substantial impact. Part of this is due to the fact that zinc oxide (ZnO) has the ability to bleed Zn+ ions, especially at pH <7. It’s these cations that are believed to be the primary issue inducing damage to coral environments. Coating mineral filters with inert materials such as silica, triethoxycaprylylsilane, and alumina help to prevent or reduce these cations. The focus on “natural” mineral sunscreens often means the inclusion of uncoated filters due to the synthetic materials used for coating being deemed as bad since they’re not also “natural”. Titanium dioxide also shows similar impact, although its impact is related to its free radical production when not coated. It’s been mentioned frequently that “reef-safe” isn’t a regulated term, with no method set to standardize what parameters to make this claim for, and the studies done also exemplify this: there’s no consistent endpoint or testing parameters (different organisms respond differently to the different UV filters), and man-made reef environments were used in various tests, along with concentrations of UV filters not realistically present in natural marine environments. References: doi:10.1007/s43630-024-00674-8. doi:10.1186/s12302-021-00515-w. doi:10.1002/ieam.4889. doi:10.1007/s43630-023-00446-w. Wong M. Is Your Sunscreen Killing Coral Reefs? The Science. Lab Muffin Beauty Science. June 6, 2025. Accessed January 15, 2026