Oxybenzone

Oxybenzone or benzophenone-3 or BP-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[4] chemical found in various flowering plants[5] 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.[6]

Oxybenzone[1]
Names
IUPAC name
(2-Hydroxy-4-methoxyphenyl)-phenylmethanone
Other names
Oxybenzone
Benzophenone-3
2-Hydroxy-4-methoxybenzophenone
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard 100.004.575
KEGG
UNII
Properties
C14H12O3
Molar mass 228.247 g·mol−1
Density 1.20 g cm−3[2]
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)[3]
Hazards[2]
NFPA 704 (fire diamond)
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilHealth code 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
1
1
0
Flash point 140.5 °C (284.9 °F; 413.6 K)
Lethal dose or concentration (LD, LC):
>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).
N verify (what is YN ?)
Infobox references

Structure and electronic structure

Being a conjugated molecule, oxybenzone absorbs light at lower energies than many aromatic molecules.[7] As in related compounds, the hydroxyl group is hydrogen bonded to the ketone.[8] 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.[9]

Production

Oxybenzone is produced by Friedel-Crafts reaction of benzoyl chloride with 3-methoxyphenol.[10]

Uses

Oxybenzone is used in plastics as an ultraviolet light absorber and stabilizer.[10] 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.[10] Oxybenzone can also be used as a photostabilizer for synthetic resins.[10] Benzophenones can leach from food packaging, and are widely used as photo-initiators to activate a chemical that dries ink faster.[11]

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.[12] It is one of the most widely used organic UVA filters in sunscreens today.[12] 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

Some debate focuses on the potential of oxybenzone as a contact allergen[12] with a 2001 study finding contact dermatitis "uncommon" for oxybenzone.[13] Due to the advent of PABA-free sunscreens, oxybenzone is now the most common allergen found in sunscreens.[14][15][16][17]

In vivo studies

The incidence of oxybenzone causing photoallergy is extremely uncommon,[13] 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.[18]

In a 2008 study of participants ages 6 and up, oxybenzone was detected in 96.8% of urine samples.[19] 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.[20] Oxybenzone is particularly penetrative because it is the most lipophilic of the three most common UV filters.[21]

When applied topically, UV filters, such as oxybenzone, are absorbed through the skin, metabolized, and excreted primarily through the urine.[22] 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).[23][24] To form DHB the methoxy functional group undergoes O-dealkylation; to form THB the same ring is hydroxylated.[22] Ring B in oxybenzone is hydroxylated to form DHMB.[22]

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.[25] The major metabolite detected was DHB and very small amounts of THB were found.[25] By utilizing the Ames test in Salmonella typhimurium strains, DHB was determined to be nonmutagenic.[26] 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."[27]

Effects on coral

Media reports link oxybenzone in sunscreens to coral bleaching,[28] although some environmental experts dispute the claim.[29] A small number of studies have been released which linked coral damage to oxybenzone exposure.[30][31] A 2015 study published in the Archives of Environmental Contamination and Toxicology led to ban of oxybenxzone containing sunscreen in Palau.[32] However, the purported link between oxybenzone and coral decline is widely discussed within the environmental community since most studies on the subject have been conducted in a lab environment.[33] 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.[34]

Health and environmental regulation

Australia

Revised as of 2007, the National Industrial Chemicals Notification and Assessment Scheme (NICNAS) Cosmetic Guidelines allow oxybenzone for cosmetic use up to 10%.[35]

Canada

Revised as of 2012, Health Canada allows oxybenzone for cosmetic use up to 6%.[36]

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.[37] It is allowed in sunscreens and cosmetics at levels of up to 6% and 0.5% respectively.[38]

Japan

Revised as of 2001, the Ministry of Health, Labour, and Welfare notification allows oxybenzone for cosmetic use up to 5%.[39]

Palau

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.[40]

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 to break it down. No regulations have come of this study yet.[10]

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%.[41]

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.[42][43]

Key West has also banned the sale of sunscreens that contain the ingredients oxybenzone (and octinoxate). The ban goes into effect on January 1, 2021.[44] However, this legislation was superseded by the Florida State Legislature by Senate Bill 172.[45] Which prohibits local governments from regulating over-the-counter proprietary drugs and cosmetics (such as sunscreen containing oxybenzone and octinoxate). The statute became effective July 1, 2020.

The City of Miami Beach, Florida voted against a ban of oxybenzone, with commissioners citing public health concerns and lack of clarity on scientific evidence supporting such a ban.[46]

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