Homosalate is an organic compound used in some sunscreens. It is formed by the Fischer-Speier esterification of salicylic acid and 3,3,5-trimethylcyclohexanol, a hydrogenated derivative of isophorone. It is found in 45% of US sunscreens as a chemical UV filter. [3] The salicylic acid part of the molecule absorbs ultraviolet rays with a wavelength of 295 nm to 315 nm to protect the skin from sun damage. Hydrophobic trimethylcyclohexyl provides greasy properties, preventing it from dissolving in water.
Similar to other UV filter compounds,[4] more homosalate was absorbed into the uppermost stratum corneum (i.e., the detachment layer) of the face (25% of the dose used) compared to the back of the volunteers. There are about two to three times as much sunscreen in the superficial stratum corneum of the face as compared to the back. Homosalate was not detected in the urine or plasma samples of volunteers in this study. [5][6]

Homosalate has been identified as an in vitro antiandrogen, [7], and has estrogenic activity at estrogen receptor alpha, [8] and general in vitro estrogenic activity. [9] Homosalate has been shown to be an antagonist of androgen and estrogen receptors in vitro. [10] Several studies have shown that organic UV filters are often cause for concern. [11]

There was no evidence homosalate of in vivo toxicity, endocrine disturbances, or adverse effects; and these adverse events have not been reported in humans.

An in vivo study involving repeated subcutaneous injections of homosalate to juvenile female Wistar rats on three consecutive days at dose levels up to 1000 mg/kg body weight showed no estrogenic potential in utero nutritional assays. Another study in immature Long-Evans rats found no estrogenic effects in vivo at up to 892 mg/kg body weight of homosalate in the daily diet. Studies in zebrafish also found no estrogenic effects after continuous exposure to homosalate for 96 hours. The SCCS states that there is insufficient evidence that pure homosalate is an endocrine disruptor in humans and further states that in vivo studies have demonstrated that homosalate has no genotoxic, phototoxic or photosensitizing effects when applied topically