Why doesn't Typology use homosalate?

For the following reasons and as a precautionary measure, we have decided to exclude homosalate from our sun care products at Typology.

Homosalate is a polluting sunscreen filter.

The primary concern raised against homosalate is its environmental impact. Indeed, this sunscreen filter is not easily biodegradable and tends to persist in marine ecosystems, where it can subsequently be found in water, sediments, or even bioaccumulated in certain aquatic organisms. This is due to its physicochemical properties: homosalate is slightly soluble in water but very lipophilic, which promotes its accumulation in living tissues. As a precaution, several countries or regions of the world, such as Florida, have begun to regulate the use of certain sunscreen filters suspected of harming marine biodiversity, particularly corals, such as oxybenzone or octocrylene. While homosalate is not yet among the filters banned in these sensitive areas, it is closely monitored for its possible ecotoxic effect.

Studies have indeed shown that homosalate is present in various waters, for instance in the rivers that run through the city of Tianjin in China, polluted with homosalate, octisalate, and octocrylene. These UV filters are then found in the bodies of certain aquatic species. In fact, research conducted in 2012 demonstrated that up to 3,100 ng/g of homosalate could be found in fish tissues, and up to 7,112 ng/g in mussels. Thus, the risk of bioaccumulation of homosalate in marine organisms is very real.

Homosalate poses a cytotoxic risk.

Homosalate has also been the subject of toxicological concerns, particularly regarding its potential effect on cell viability. A recent study, conducted on the human breast cell line MCF-7, highlighted a dose-dependent cellular toxicity from concentrations exceeding 1,000 µM. At these doses, cell viability begins to significantly decrease, dropping to 57% at 2,000 µM. Furthermore, at concentrations of 750 to 1,000 µM, a significant formation of micronuclei was observed after 24 hours of exposure. Micronuclei are classic markers of genotoxic damage: they indicate the presence of chromosomal fragments not integrated into the nucleus during cell division. This phenomenon can reflect either DNA damage or a defect in the cell repair system. Homosalate also proved to be clastogenic under these conditions, that is, capable of inducing structural chromosomal aberrations, a worrying characteristic that raises concerns about potential carcinogenicity.

Note : These concentrations are higher than those found in skincare products. However, these figures fuel the growing concerns about this UV filter, particularly regarding its long-term safety.

It appears that Homosalate may be able to penetrate the skin barrier.

Another concerning point: homosalate could potentially cross the skin barrier and enter the bloodstream. In 2020, a study conducted by FDA researchers assessed the plasma concentrations of several sun filters, including homosalate, seven days after application four times a day for four days on 75% of the body surface at a rate of 2mg/cm², the recommended dose for a sun protection effectiveness. The plasma concentrations of homosalate reached 23.1 ng/mL, levels exceeding the maximum recommended threshold of 0.5 ng/mL set by the FDA.

Animal studies align with this. Research conducted on rats evaluated the skin penetration of homosalate in different formulations (vaseline, oily solution, lotion, and gel). The gel proved to be the best carrier, with a systemic bioavailability of 4 to 5% after topical application. Once in circulation, homosalate presents a high volume of distribution (13 to 17 L/kg) and a prolonged elimination half-life (up to 26 hours), which indicates a significant persistence in the body. This pharmacokinetic profile, combined with the filter's ability to cross the skin barrier, raises questions about its potential cumulative effect.

Homosalate is suspected to be an endocrine disruptor.

One of the most sensitive issues regarding homosalate concerns its potential effect on the hormonal system. Studies have sought to determine whether this UV filter could interact with human hormonal receptors, particularly oestrogen receptors (ER). An initial study, using a binding test in vitro between the alpha type oestrogen receptor and radio-labelled estradiol, concluded that homosalate did not show any direct affinity with the oestrogen receptor, even at very high concentrations (up to 100 mM). Prima facie, one could therefore think that homosalate does not possess oestrogenic properties.

However, a second study, based on a cellular test, observed different results. Using modified embryonic human cells (293HEK) to express human hormonal receptors and an estrogen-activated reporter gene, researchers found that homosalate activated the transcription of the alpha-type estrogen receptor (ERα). Partial activation was also observed with the ERβ receptor. These results suggest a low to moderate estrogenic potential of homosalate, which cannot be completely disregarded.

As of now, the Scientific Committee on Consumer Safety (SCCS) believes that the available data does not allow for a definitive conclusion regarding the endocrine-disrupting nature of homosalate. However, it acknowledges the existence of concerning signals and calls for further studies.