Mineral sunscreens have emerged as a substitute for chemical sunscreens in the attempt to protect key ecosystems such as coral reefs. However, our in-depth microcosm study and field investigations into mineral sunscreens reveal irreversible damages to corals and potential pollution for the coral reef environment. This unveils a novel threat to coral reefs, underscoring the imperative for a well-rounded approach to future sunscreen use and sustainable coral conservation.