Oxybenzone Explained

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.[1] In nature, it can be found in various flowering plants (angiosperms).[2] 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).[3] As a result, sunscreens containing oxybenzone have been banned from sale in Hawaii, Palau,[4] and Thailand.[5]

Structure and electronic structure

Being a conjugated molecule, oxybenzone absorbs light at lower energies than many aromatic molecules.[6] As in related compounds, the hydroxyl group is hydrogen bonded to the ketone.[7] 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.[8]

Production

Oxybenzone is produced by the Friedel-Crafts reaction of benzoyl chloride with 3-methoxyphenol.[9]

Uses

Oxybenzone is used in plastics as an ultraviolet light absorber and stabilizer.[9] 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.[9] Oxybenzone can also be used as a photostabilizer for synthetic resins.[9] This substance can leach from food packaging, and is widely used as photo-initiators to activate a chemical that dries ink faster.[10] 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.[11]

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.[12] Some brands market their sunscreens as "oxybenzone free"[13] 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,[14] 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.[15] Evidence points to oxybenzone having contact allergen effects. Oxybenzone is allegedly the most common allergen found in sunscreens.[16] [17] [18] [19]

In a 2008 study of participants ages 6 and up, oxybenzone was detected in 96.8% of urine samples.[20] 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.[21] 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.[22]

When applied topically, UV filters, such as oxybenzone, are absorbed through the skin, metabolized, and excreted primarily through the urine.[23] 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).[24] [25] To form DHB the methoxy functional group undergoes O-dealkylation; to form THB the same ring is hydroxylated.[23] Ring B in oxybenzone is hydroxylated to form DHMB.[23]

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.[26] The major metabolite detected was DHB and very small amounts of THB were found.[26] By utilizing the Ames test in Salmonella typhimurium strains, DHB was determined to be nonmutagenic.[27] 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."[28] Oxybenzone can also occur as a natural product.[29] [30]

Environmental effects

Studies have shown possible links between oxybenzone exposure and mortality in coral larvae, coral bleaching, and to genetic damage in marine invertebrates.[31] [32] [33] [34] [35] [36] However, some of these studies have been criticised for not having control groups or representing real-world conditions.[37] [38] [39] [40] Nevertheless, these have led to the ban of oxybenzone-containing sunscreen in many areas[41] such as Palau,[42] Hawaii, nature reserves in Mexico, Bonaire, the Marshall Islands, the United States Virgin Islands, Thailand's marine natural parks,[43] the Northern Mariana Islands,[44] and Aruba.

Health and environmental regulation

Aruba

Aruba banned the use of oxybenzone in sunscreens due to environmental concerns in 2019.[45]

Australia

As of 2023, the maximum concentration of oxybenzone in a sunscreen cannot exceed 10% according to the TGA (Therapeutic Goods Administration).[46]

Bonaire

As of 2019 Bonaire banned oxybenzone due to coral toxicity concerns, with regards to coral larvae[47]

Canada

Revised as of 2012, Health Canada allows oxybenzone for cosmetic use up to 6%.[48]

European Union

The European Food Safety Authority categorises All the benzophenones, such as oxybenzone, as persistent, bio-accumulative, toxic, and a possible human carcinogen and endocrine disruptor.[49] The Scientific Committee on Consumer Products (SCCP) of the European Commission concluded that it poses a significant risk to consumers as a contact allergenic potential.[50] It is allowed in face, hand, and lip products up to 6%, in body products up to 2.2%, and in other formulations up to 0.5%.[51]

Japan

Revised as of 2001, the Ministry of Health, Labour, and Welfare notification allows oxybenzone for cosmetic use up to 5%.[52]

Mexico

Nature Reserves across Mexico have banned the usage of sunscreens containing Oxybenzone[53]

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 came into force in 2020.[54] [55]

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.[9]

Thailand

Thailand has prohibited sunscreens containing chemicals harmful to corals, including oxybenzone, in all its marine national parks. This decision was driven by evidence highlighting the detrimental effects of certain sunscreen ingredients on coral larvae, reproduction, and inducing reef bleaching. Violators face fines up to 100,000 baht (£2,100), although enforcement methods remain unspecified.[56]

United States

In 2021 the U.S. FDA changed their classification of oxybenzone and no longer regard it as GRASE (Generally Recognised As Safe and Effective)[57] due to the lack of safety data to support the classification.

The Hawaii State Legislature has legislated oxybenzone as illegal for use in sunscreens and personal care products since 2021 due to its environmental effects, such as mortality in developing coral, coral bleaching, genetic damage to coral, and other marine organisms.[58] [59]

Key West has also banned the sale of sunscreens that contain the ingredients oxybenzone (and octinoxate). The ban was to be effective as of January 1, 2021.[60] However, this legislation was superseded by the Florida State Legislature by Senate Bill 172,[61] 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.

Notes and References

  1. Web site: Oxybenzone - Substance Information - ECHA . echa.europa.eu . 2019-05-01.
  2. Web site: Benzophenone-3 (BP-3) Factsheet National Biomonitoring Program CDC. 2019-05-24. www.cdc.gov. 2019-05-29.
  3. Web site: Oxybenzone Offers Sun Protection—At a Cost. Byrdie.
  4. Web site: Palau is first country to ban 'reef toxic' sun cream. January 1, 2020. www.bbc.com.
  5. Web site: Thailand bans coral-damaging sunscreens in marine parks. August 4, 2021. www.bbc.com.
  6. Castro GT, Blanco SE, Giordano OS . 10.3390/50300424 . UV Spectral Properties of Benzophenone. Influence of Solvents and Substituents . 2000 . Molecules . 5 . 3 . 424–425 . free .
  7. Lago AF, Jimenez P, Herrero R, Dávalos JZ, Abboud JL . Thermochemistry and gas-phase ion energetics of 2-hydroxy-4-methoxy-benzophenone (oxybenzone) . The Journal of Physical Chemistry A . 112 . 14 . 3201–8 . April 2008 . 18341312 . 10.1021/jp7111999 . 2008JPCA..112.3201L .
  8. Chrétien MN, Heafey E, Scaiano JC . Reducing adverse effects from UV sunscreens by zeolite encapsulation: comparison of oxybenzone in solution and in zeolites . Photochemistry and Photobiology . 86 . 1 . 153–61 . 2010 . 19930122 . 10.1111/j.1751-1097.2009.00644.x . 43408456 .
  9. Web site: Hazardous Substances Data Bank . 2-HYDROXY-4-METHOXYBENZOPHENONE . National Library of Medicine (US), Division of Specialized Information Services . 9 March 2014.
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  12. Web site: Edney. Anna . 2023-05-24 . There's Still Scary Stuff in Sunscreen . 2023-08-15. www.bloomberg.com . en.
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  26. Sarveiya V, Risk S, Benson HA . Liquid chromatographic assay for common sunscreen agents: application to in vivo assessment of skin penetration and systemic absorption in human volunteers . Journal of Chromatography. B, Analytical Technologies in the Biomedical and Life Sciences . 803 . 2 . 225–31 . April 2004 . 15063329 . 10.1016/j.jchromb.2003.12.022 .
  27. "Hazardous Substances Data Bank". 2,4-Dihydroxybenzophenone. National Library of Medicine (US), Division of Specialized Information Services. Retrieved 19 April 2014.
  28. Office of the Commissioner . 2019-05-09. FDA finalizes recommendations for studying absorption of active ingredients in topically-applied OTC monograph drugs. FDA. en.
  29. Web site: 2017-12-01 . Benzophenone-3 (BP-3) Factsheet . 2019-05-01 . www.cdc.gov.
  30. Web site: 2019-05-24 . Benzophenone-3 (BP-3) Factsheet National Biomonitoring Program CDC . 2019-05-29 . www.cdc.gov.
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  36. Downs . C. A. . Bishop . Elizabeth . Diaz-Cruz . M. Silvia . Haghshenas . S. Abbas . Stien . Didier . Rodrigues . Alice M. S. . Woodley . Cheryl M. . Sunyer-Caldú . Adrià . Doust . Shadan Nasseri . Espero . William . Ward . Gene . Farhangmehr . Aref . Tabatabaee Samimi . S. Maryam . Risk . Michael J. . Lebaron . Philippe . 2022-03-01 . Oxybenzone contamination from sunscreen pollution and its ecological threat to Hanauma Bay, Oahu, Hawaii, U.S.A. . Chemosphere . en . 291 . Pt 2 . 132880 . 10.1016/j.chemosphere.2021.132880 . 34780745 . 2022Chmsp.291m2880D . 10261/257615 . 244095190 . 0045-6535. free .
  37. Web site: Hughes . Terry . vanc . There's insufficient evidence your sunscreen harms coral reefs .
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  40. Web site: PubPeer criticism of Downs, et al. .
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  42. News: McGrath . Matt . vanc . November 2018 . Coral: Palau to ban sunscreen products to protect reefs . BBC News . BBC . 2020-01-01.
  43. Web site: 2021-08-04 . Thailand bans coral-damaging sunscreens . 2022-11-02 . France 24 . en.
  44. Web site: Torres . Governor Ralph . April 2020 . COMMONWEAlTH of the NORTHERN l\fARlANA ISLANDS - OFFICE OF THE GOVERNOR . Commonwealth Law Revision Commission.
  45. Web site: Overheid . Aruba . 2019-11-21 . Single use plastic, the use of Styrofoam and Oxybenzone prohibited! . 2022-11-02 . www.government.aw . en.
  46. Web site: May 2023 . Active ingredients currently restricted for use in therapeutic sunscreens . Australian Government: TGA, ARGS, Department of Health and Aged Care . 40.
  47. Web site: Stephanie Pappas . 2018-05-17 . Another Tropical Paradise Enacts a Sunscreen Ban . 2023-08-18 . livescience.com . en.
  48. Web site: Guidance Document Sunscreen Monograph. Health Canada. 9 March 2014. 2012-12-03.
  49. Web site: March 2019 . Endocrine Disruptors: from Scientific Evidence to Human Health Protection . European Parliament . European Parliament - Policy Department for Citizens' Rights and Constitutional Affairs - Directorate General for Internal Policies of the Union PE 608.866.
  50. Web site: Aguirre . Claudia . vanc . Shedding Light on Sun Safety – Part Two . The International Dermal Institute . 9 March 2014 . 19 May 2014 . https://web.archive.org/web/20140519123813/http://dermalinstitute.com/us/library/66_article_Shedding_Light_on_Sun_Safety_Part_Two.html . dead .
  51. Web site: COMMISSION REGULATION (EU) 2022/1176.
  52. Web site: Standards for Cosmetics . Ministry of Health and Welfare Notification No.331 of 2000 . Japanese Government . 9 March 2014.
  53. Miller . Ingo B. . Pawlowski . Sascha . Kellermann . Matthias Y. . Petersen-Thiery . Mechtild . Moeller . Mareen . Nietzer . Samuel . Schupp . Peter J. . 2021-06-26 . Toxic effects of UV filters from sunscreens on coral reefs revisited: regulatory aspects for "reef safe" products . Environmental Sciences Europe . 33 . 1 . 74 . 10.1186/s12302-021-00515-w . 2190-4715 . free .
  54. News: Palau to ban sunscreen to save coral reefs . BBC News . November 2018 . McGrath . Matt . vanc .
  55. Web site: The Republic of Palau Adopts the World's Strictest National Sunscreen Standard – PalauGov.pw . 2023-08-18 . en-US.
  56. News: 2021-08-04 . Thailand bans coral-damaging sunscreens in marine parks . en-GB . BBC News . 2023-08-18.
  57. Research . Center for Drug Evaluation and . 2021-11-16 . Questions and Answers: FDA posts deemed final order and proposed order for over-the-counter sunscreen . FDA . en.
  58. News: Folley . Aris . vanc . 2 May 2018 . Hawaii lawmakers approve ban on sunscreens with chemicals harmful to coral reefs . The Hill . 2 May 2018.
  59. Galamgam J, Linou N, Linos E . November 2018 . Sunscreens, cancer, and protecting our planet . The Lancet. Planetary Health . 2 . 11 . e465–e466 . 10.1016/S2542-5196(18)30224-9 . 30396433 . free.
  60. News: Filosa . Gwen . vanc . Key West bans the sale of sunscreens that hurt coral reefs in the Keys . 6 February 2019 . Miami Herald . February 5, 2019.
  61. Web site: SB 172: Florida Drug and Cosmetic Act . 2020-11-10 . The Florida Senate.

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