Oxybenzone or benzophenone-3 (trade names Milestab 9, Eusolex 4360, Escalol 567, KAHSCREEN BZ-3) is an organic compound. It is a pale-yellow solid that is readily soluble in most organic solvents. Oxybenzone belongs to the class of aromatic ketones known as benzophenones. It is a naturally occurring chemical found in various flowering plants as well as being an organic component of many sunscreen lotions. It is also in widespread use in things like plastics, toys, furniture finishes, and more to limit UV degradation.
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||228.247 g·mol−1|
|Density||1.20 g cm−3|
|Melting point||62 to 65 °C (144 to 149 °F; 335 to 338 K)|
|Boiling point||224 to 227 °C (435 to 441 °F; 497 to 500 K)|
|Acidity (pKa)||7.6 (H2O)|
|Flash point||140.5 °C (284.9 °F; 413.6 K)|
|Lethal dose or concentration (LD, LC):|
LD50 (median dose)
|>12800 mg/kg (oral in rats)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Structure and electronic structureEdit
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.
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.
Some debate focuses on the potential of oxybenzone as a contact allergen with a 2001 study finding contact dermatitis "uncommon" for oxybenzone. Due to the advent of PABA-free sunscreens, oxybenzone is now the most common allergen found in sunscreens.
In vivo studiesEdit
The incidence of oxybenzone causing photoallergy 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.
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 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."
Effects on coralEdit
Media reports link oxybenzone in sunscreens to coral bleaching, although some environmental experts dispute the claim. A 2015 study published in the Archives of Environmental Contamination and Toxicology linked oxybenzone to effects on cell culture experiments and juvenile coral, but the study has no environmental relevance and was fraught with methodological errors and poorly controlled. However, the purported link between oxybenzone and coral decline is widely disputed within the environmental community. A 2019 study of UV filters in oceans found far lower concentrations of oxybenzone than previously reported, and lower than known thresholds for environmental toxicity. Additionally, the National Oceanic and Atmospheric Administration (NOAA) has indicated that coral decline is instead associated with effects from climate change (warming oceans, rising water levels, acidification), overfishing, and pollution from agriculture, wastewater, and urban run-off.
Health and environmental regulationEdit
Revised as of 2007, the National Industrial Chemicals Notification and Assessment Scheme (NICNAS) Cosmetic Guidelines allow oxybenzone for cosmetic use up to 10%.
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 sunscreens and cosmetics at levels of up to 6% and 0.5% respectively.
The Palau government has signed a law that restricts the sale and use of sunscreen and skincare products that contain oxybenzone, and nine other chemicals. The ban comes into force in 2020.
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.
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%.
The Hawaii State Legislature has passed a bill that would prohibit the sale of non-prescription sunscreens containing oxybenzone and other chemicals that may be damaging to coral reefs (e.g. octyl methoxycinnamate), effective January 1, 2021.
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