Homosalate is an

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

used in some

sunscreen Sunscreen, also known as sunblock, sun lotion or sun cream, is a photoprotection, photoprotective topical product for the Human skin, skin that helps protect against sunburn and prevent skin cancer. Sunscreens come as lotions, sprays, gels, fo ...

s. It is made by the

Fischer–Speier esterification Fischer esterification or Fischer–Speier esterification is a special type of esterification by refluxing a carboxylic acid and an Alcohol (chemistry), alcohol in the presence of an acid catalyst. The reaction was first described by Emil Fischer ...

salicylic acid Salicylic acid is an organic compound with the formula HOC6H4COOH. A colorless (or white), bitter-tasting solid, it is a precursor to and a active metabolite, metabolite of acetylsalicylic acid (aspirin). It is a plant hormone, and has been lis ...

and 3,3,5-trimethylcyclohexanol, the latter being a hydrogenated derivative of isophorone. Contained in 45% of U.S. sunscreens, it is used as a chemical UV filter. The salicylic acid portion of the molecule absorbs

ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...

rays with a wavelength from 295 nm to 315 nm, protecting the skin from sun damage. The

hydrophobic In chemistry, hydrophobicity is the chemical property of a molecule (called a hydrophobe) that is seemingly repelled from a mass of water. In contrast, hydrophiles are attracted to water. Hydrophobic molecules tend to be nonpolar and, thu ...

trimethyl cyclohexyl group provides greasiness that prevents it from dissolving in water.

Safety

Homosalate was identified in a court case brought by German chemical company Symrise who claimed that the ingredient used in sunscreen did not require animal testing. Symrise lost the appeal against a European Chemicals Agency (ECHA) decision that requires the German manufacturer to test sunscreen ingredients on animals. The Court of Justice of the European Union (CJEU) decision applies to two formerly approved ingredients used exclusively in sunscreens — UV filter homosalate and 2-ethylhexyl salicylate. Similar to other UV filter compounds, more homosalate is absorbed into the uppermost stratum corneum (''ie, the stratum disjunctum'') of the face (25% of applied dose) versus back of volunteers. This amounted to approximately two to three times the amount of sunscreen that was present in the superficial

stratum corneum The stratum corneum (Latin language, Latin for 'horny layer') is the outermost layer of the epidermis (skin), epidermis. Consisting of dead tissue, it protects underlying tissue from infection, dehydration, chemicals and mechanical stress. It is ...

layers of the face compared with the back. There was no homosalate detected in the urine samples or

blood plasma Blood plasma is a light Amber (color), amber-colored liquid component of blood in which blood cells are absent, but which contains Blood protein, proteins and other constituents of whole blood in Suspension (chemistry), suspension. It makes up ...

samples of the volunteers in this study. Homosalate has been identified as an antiandrogen (testosterone blocker) ''in vitro'', as well as having estrogenic activity toward estrogen receptors α, and general ''in vitro'' estrogenic activity. Homosalate has been shown to be an antagonist toward

androgen An androgen (from Greek ''andr-'', the stem of the word meaning ) is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. This includes ...

and

estrogen Estrogen (also spelled oestrogen in British English; see spelling differences) is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three ...

receptors ''

in vitro ''In vitro'' (meaning ''in glass'', or ''in the glass'') Research, studies are performed with Cell (biology), cells or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in ...

''. Some work has shown that organic UV filters in general can present concerns. There is no ''

in vivo Studies that are ''in vivo'' (Latin for "within the living"; often not italicized in English) are those in which the effects of various biological entities are tested on whole, living organisms or cells, usually animals, including humans, an ...

'' evidence of toxicity, endocrine disfunction or adverse effects; and none of these adverse events have ever been reported to occur in humans. An ''in vivo'' study involving repeated subcutaneous injections of homosalate at dose levels up to 1000mg/kg of body weight to juvenile female Wistar rats over three consecutive days revealed no estrogenic potential in the uterotrophic assay. Another study on immature Long–Evans rats receiving up to 892 mg/kg of body weight of homosalate in their daily diet found no estrogenic effects in vivo. Research on zebra fish also found no estrogenic effects after being continuously exposed to homosalate for 96 hours straight. The SCCS has declared there is no sufficient evidence that identifies pure homosalate as an endocrine disruptor in humans and further declared that ''in vivo'' research has confirmed that homosalate has no genotoxic, phototoxic or

photosensitive Photosensitivity is the amount to which an object reacts upon receiving photons, especially visible light. In medicine, the term is principally used for abnormal reactions of the skin, and two types are distinguished, photoallergy and phototoxicity. ...

effects when applied topically.

References

{{Salicylates 3,3,5-Trimethylcyclohexyl esters Salicylate esters Sunscreening agents 3-Hydroxypropenals