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 295nm to 315nm to protect the skin from sun damage. Hydrophobic trimethylcyclohexyl provides a greasy feel and prevents it from dissolving in water.
Similar to other UV filter compounds,[4] more homosalate was absorbed into the uppermost stratum corneum (i.e., the separating layer) of the face (25% of the applied dose) compared to volunteers. This is about two to three times the amount of sunscreen in the stratum corneum, the upper layer of the face, compared to the back. Homosalate was not detected in the volunteers' urine or plasma samples in the study. [5] [6]

Homosalate has been identified as an antiandrogen in vitro,[7] as well as 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 of in vivo toxicity, endocrine dysfunction, or adverse effects; and none of these adverse events have been reported in homosalate humans.

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