Oxybenzone or benzophenone-3 or BP-3 (trade names Milestab 9, Eusolex 4360, Escalol 567, KAHSCREEN BZ-3) is an organic compound belonging to the class of aromatic ketones known as benzophenones. It takes the form of pale-yellow crystals that are readily soluble in most organic solvents. It is widely used in sunscreen formulations, plastics, toys, furniture finishes, and other products to limit UV degradation. In nature, it can be found in various flowering plants (angiosperms). The compound was first synthesised in Germany by chemists König and Kostanecki in 1906. The use of oxybenzone as sunscreen ingredient is currently under scrutiny by the scientific community due to controversies about the molecule's environmental impact and safety profile (see section below). As a result, sunscreens containing oxybenzone have been banned from sale in Hawaii, Palau, and Thailand.
Structure and electronic structure Being a conjugated molecule, oxybenzone absorbs light at lower energies than many aromatic molecules. As in related compounds, the hydroxyl group is hydrogen bonded to the ketone. This interaction contributes to oxybenzone's light-absorption properties. At low temperatures, however, it is possible to observe both the phosphorescence and the triplet-triplet absorption spectrum. At 175 K the triplet lifetime is 24 ns. The short lifetime has been attributed to a fast intramolecular hydrogen transfer between the oxygen of the C=O and the OH.
Production Oxybenzone is produced by the Friedel-Crafts reaction of benzoyl chloride with 3-methoxyphenol.
Uses Oxybenzone is used in plastics as an ultraviolet light absorber and stabilizer. It is used, along with other benzophenones, in sunscreens, hair sprays, and cosmetics because they help prevent potential damage from sunlight exposure. It is also found, as a stabilizer in concentrations up to 1%, in nail polishes. Oxybenzone can also be used as a photostabilizer for synthetic resins. This substance can leach from food packaging, and is widely used as photo-initiators to activate a chemical that dries ink faster. Despite its photoprotective qualities, much controversy surrounds oxybenzone because of possible negative hormonal and photoallergenic effects, leading many countries to regulate use in sunscreen products.
Sunscreen Oxybenzone provides a broad-spectrum ultraviolet coverage which includes UVB and short-wave UVA rays. As a photoprotective agent, it has an absorption profile spanning from 270 to 350 nm with absorption peaks at 288 and 350 nm. Due to toxicity and environmental concerns, the percentage of sunscreen products on the market containing oxybenzone in the USA dropped to 13% in 2023 from 60% in 2019. Some brands market their sunscreens as "oxybenzone free" due to the generally negative perception of benzophenones by both the consuming public and scientific researchers.
Safety
In vivo studies The incidence of oxybenzone causing skin eruptions is extremely uncommon, however, oxybenzone has been associated with rare allergic reactions triggered by sun exposure. In a study of 82 patients with photoallergic contact dermatitis, just over one quarter showed photoallergic reactions to oxybenzone. Evidence points to oxybenzone having contact allergen effects. Oxybenzone is allegedly the most common allergen found in sunscreens. In a 2008 study of participants ages 6 and up, oxybenzone was detected in 96.8% of urine samples. Humans can absorb anywhere from 0.4% to 8.7% of oxybenzone after one topical application of sunscreen, as measured in urine excretions. This number can increase after multiple applications over the same period of time. Because oxybenzone is the least lipophilic of the three most common UV filters, it is the least likely to end up trapped in the stratum corneum and the most likely to be absorbed and metabolized. When applied topically, UV filters, such as oxybenzone, are absorbed through the skin, metabolized, and excreted primarily through the urine. The method of biotransformation, the process by which a foreign compound is chemically transformed to form a metabolite, was determined by Okereke and colleagues through oral and dermal administration of oxybenzone to rats. The scientists analyzed blood, urine, feces, and tissue samples and found three metabolites: 2,4-dihydroxybenzophenone (DHB), 2,2-dihydroxy-4-methoxybenzophenone (DHMB) and 2,3,4-trihydroxybenzophenone (THB). To form DHB the methoxy functional group undergoes O-dealkylation; to form THB the same ring is hydroxylated. Ring B in oxybenzone is hydroxylated to form DHMB. A study done in 2004 measured the levels of oxybenzone and its metabolites in urine. After topical application to human volunteers, results revealed that up to 1% of the applied dose was found in the urine. The major metabolite detected was DHB and very small amounts of THB were found. By utilizing the Ames test in Salmonella typhimurium strains, DHB was determined to be nonmutagenic. In 2019, the U.S. Food and Drug Administration (FDA) noted in their recommendations for future study that, "While research indicates that some topical drugs can be absorbed into the body through the skin, this does not mean these drugs are unsafe." Oxybenzone can also occur as a natural product.
Environmental effects Studies have shown possible links between oxybenzone exposure and mortality in coral larvae, coral bleaching, and to genetic damage in marine invertebrates. However, some of these studies have been criticised for not having control groups or representing real-world conditions. Nevertheless, these have led to the ban of oxybenzone-containing sunscreen in many areas such as Palau, Hawaii, nature reserves in Mexico, Bonaire, the Marshall Islands, the United States Virgin Islands, Thailand's marine natural parks, the Northern Mariana Islands, and Aruba.
Health and environmental regulation
Aruba Aruba banned the use of oxybenzone in sunscreens due to environmental concerns in 2019.
Australia As of 2023, the maximum concentration of oxybenzone in a sunscreen cannot exceed 10% according to the TGA (Therapeutic Goods Administration).
Bonaire As of 2019 Bonaire banned oxybenzone due to coral toxicity concerns, with regards to coral larvae
Canada Revised as of 2012, Health Canada allows oxybenzone for cosmetic use up to 6%.
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