Sunscreens contain either inorganic chemicals (zinc oxide, titanium dioxide, etc.) that reflect or scatter UV rays, or organic chemicals (avobenzone, oxybenzone, etc.) that absorb UV rays through their chemical bonds so your skin doesn’t absorb them. Inorganic chemicals act as a physical sunblock, and were often seen on totally rad beachgoers and surfers in the 1980s and 90s. These days manufacturers make the particles much smaller so the white is less visible.
Sunscreens are manufactured by mixing together raw materials with purified water in large vats, which are then injected into plastic containers on an automated assembly line. A study by Valisure, a pharmacy and research testing lab, found 78 out of 294 sunscreen batches from 69 companies contained benzene, despite the fact that benzene is not an ingredient in any of the products. Benzene is a chemical formed by natural processes, such as volcanoes and forest fires, and by humans, and has been linked to blood cancers such as leukemia. No one is sure how benzene found its way into so many batches of sunscreen, but the assumption is accidental contamination. If you are concerned about the sunscreen in your home, you can check the complete list of sunscreens that tested positive for benzene here.
Coral reefs have been dying from bleaching with a frequency that has increased dramatically over the past 20 years. This is troubling because coral reefs are the most biologically productive and diverse ecosystems in the world, providing food protein for half a billion people. An algae that lives in healthy coral tissues provides nutrients to the reefs through photosynthesis, and also helps to make coral reefs the beautiful colors that they are known for. When these algae die or leave the reef, the corals are thus exposed and die. One source of coral bleaching is the chemicals in sunscreen that wash off of our bodies and enter our waterways when we swim or shower.
In 2008, scientists at the Polytechnic University of the Marche Region in Ancona, Italy, studied the effects of sunscreen exposure on samples of tropical reefs. They found that four common sunscreen ingredients stimulated dormant viral infections in the algae, killing not only the host algae, but also infecting nearby coral communities. This study was bolstered by a 2016 study performed by the National Oceanic and Atmospheric Administration (NOAA) that found very similar results, as well as DNA damage and growth abnormalities. The devastating effects of these chemicals on coral reefs and other marine life is still being studied, so the full extent is not yet known.
On January 1, 2020, the western Pacific nation of Palau was the first country to ban certain chemicals in sunscreens. Other places that have banned some of these chemicals include Hawaii, parts of Mexico, Bonaire, Aruba, the U.S. Virgin Islands. The Coral Reef Alliance recommends wearing UPF clothing and a hat, avoiding spray on sunscreens, and using mineral-based sunscreens when needed to help protect our coral reefs.