Oxybenzone

Structure and electronic structure

Being a conjugated molecule, oxybenzone absorbs 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 Friedel-Crafts reaction of benzoyl chloride with 3-methoxyphenol(3-hydroxyanisole).

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, in concentrations up to 1%, in nail polishes. Oxybenzone can also be used as a photostabilizer for synthetic resins. Benzophenones can leach from food packaging, and are widely used as photo-initiators to activate a chemical that dries ink faster.

As a sunscreen, it provides broad-spectrum ultraviolet coverage, including 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. It is one of the most widely used organic UVA filters in sunscreens today. It is also found in nail polish, fragrances, hairspray, and cosmetics as a photostabilizer. Despite its photoprotective qualities, much controversy surrounds oxybenzone because of its possible hormonal and photoallergenic effects, leading many countries to regulate its use.

Safety and controversy

Some debate focuses on the potential of oxybenzone as an endocrine disruptor. According to the Environmental Working Group (EWG) oxybenzone is ineffective and harmful. Similar concerns have been expressed for related products including avobenzone, octisalate, octocrylene, homosalate, and octinoxate. Due to the advent of PABA-free sunscreens, oxybenzone is now the most common allergen found in sunscreens.

In vivo studies

Among common sunscreen chemicals, oxybenzone is associated with allergic reactions triggered by sun exposure. In a study of 82 patients with photoallergic contact dermatitis, over one quarter showed photoallergic reactions to oxybenzone.

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. Oxybenzone is particularly penetrative because it is the most lipophilic of the three most common UV filters.

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 determinated to be nonmutagenic.

Effects on coral

Benzophenones (along with three other active ingredients) in sunscreens have been linked to coral bleaching and die-offs. A 2015 study published by the Archives of Environmental Contamination and Toxicology directly linked oxybenzone to the declining health of coral reefs popular with tourists.

Australia

Revised as of 2007, the National Industrial Chemicals Notification and Assessment Scheme (NICNAS)) Cosmetic Guidelines allow oxybenzone for cosmetic use up to 10%.

Canada

Revised as of 2012, Health Canada allows oxybenzone for cosmetic use up to 6%.

European Union

The Scientific Committee on Consumer Products (SCCP) of the European Commission concluded in 2008 that it does not pose a significant risk to consumers, apart from contact allergenic potential. It is allowed in cosmetics up to 10%.

Japan

Revised as of 2001, the Ministry of Health, Labour, and Welfare notification allows oxybenzone for cosmetic use up to 5%.

Sweden

The Swedish Research Council has determined that sunscreens with oxybenzone are unsuitable for use in young children, because children under the age of two years have not fully developed the enzymes that are believed break it down. No regulations have come of this study yet.

United States

Oxybenzone was approved for use in the US by the FDA in the early 1980s. Revised as of April 1, 2013, the FDA allows oxybenzone in OTC sunscreen products up to 6%.