Why doesn't Typology use homosalate?

Derived from carbon, homosalate is an organic sun filter found in the composition of many sun creams. It is valued for its ability to absorb UVB rays, which are responsible for tanning, sunburn, and also implicated in the occurrence of skin cancers. While the use of homosalate as a sun filter was limited to 10%, the European Scientific Committee has now restricted it to 7.34%. In other countries, such as the United States, the concentration of homosalate in sun products can reach 15%. It is worth noting that homosalate is one of the nine UV filters authorised worldwide, including octocrylene and oxybenzone.

The photoprotective power of homosalate is based on its unique chemical structure. This derivative of salicylic acid has a conjugated aromatic nucleus linked to an ester group, which gives it the ability to absorb light energy in the UVB region, between 295 and 315 nm. When a photon hits the molecule, it absorbs this energy and quickly dissipates it as heat, thus preventing UV rays from damaging the DNA of skin cells.

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.

• Règlement (CE) n°1223/2009 du Parlement Européen et du Conseil.

• BARSELO D. & al. An overview of UV-absorbing compounds (organic UV filters) in aquatic biota. Analytical and Bioanalytical Chemistry (2012).

• DONG YOO S. & al. Percutaneous absorption, disposition, and exposure assessment of homosalate, a UV filtering agent, in rats. Journal of Toxicology and Environmental Health (2014).

• MATTA M. K. & al. Effect of Sunscreen Application Under Maximal Use Conditions on Plasma Concentration of Sunscreen Active Ingredients: A Randomized Clinical Trial. JAMA (2019).

• YAZAR S. & al. Assessment of the cytotoxicity and genotoxicity of homosalate in MCF-7. Journal of Cosmetic Dermatology (2020).

• Scientific Committee on Consumer Safety (SCCS). Opinion on Homosalate (2021).

• ALMEIDA I. F. & al. UV Filters: Challenges and Prospects. Pharmaceuticals (2022).

• CARDAMONE E. & al. Use of Physiologically-Based Kinetics Modelling to Reliably Predict Internal Concentrations of the UV Filter, Homosalate, After Repeated Oral and Topical Application. Frontiers in Pharmacology (2022).

• TANG Z. & al. Occurrence and distribution of organic ultraviolet absorbents in sediments from small urban rivers, Tianjin, China: Implications for risk management. Ecotoxicology and Environmental Safety (2022).

• ROTONDI M. & al. In vitro study of the UV-filter homosalate effects on rat and human thyroid cells. Environmental Pollution (2024).