Risks associated with MBBT sunscreen filter?

Methylene bis-benzotriazolyl tetramethylbutylphenol, a contentious UV filter.

Methylene bis-benzotriazolyl tetramethylbutylphenol, more commonly known as MBBT, is an organic organic UV filter found in many sun protection products, but not Typology's. It has the unique characteristic of having a broad UV absorption spectrum (290 to 400 nm). Furthermore, due to its chemical structure, which includes two benzotriazole groups connected by a methylene bridge, it has excellent photostability, meaning the molecule resists degradation when exposed to sunlight. From a regulatory perspective, the use of MBBT is permitted up to 10% in the European Union and this UV filter is listed in Annex IV of Regulation (EC) No 1223/2009. However, it is not authorised in the United States, where the regulatory validation of UV filters is complicated due to the special status of sun protection products, which are considered as drugs.

In sun care products, MBBT can be found in two forms: nanoparticulate and non-nanoparticulate. The nano form allows for better dispersion and transparency on the skin, avoiding any white effect, but both forms are equally effective in terms of UV protection. Both raise questions about the risks they pose to the skin and health of users, as well as to the environment.

Structure chimique du MBBT. — Chemical structure of MBBT.
Source: Scientific Committee on Consumer Safety (SCCS). Opinion on 2,2'-Methylene-bis-(6-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol) (nano form). Submission III COLIPA No. 579 (2015).

MBBT is a substance that is minimally absorbed but highly persistent.

According to assessments by the Scientific Committee on Consumer Safety (SCCS), MBBT exhibits very low skin absorption. A study in vitro showed that only 0.02% of the applied molecule in its nano form penetrated intact human skin, and about 0.07% on damaged skin. This implies that the systemic risk associated with skin exposure remains limited. These results are reassuring, especially since nanoparticles raise concerns due to their small size, which could allow them to cross the skin barrier.

As a precautionary measure, we do not use nanoparticles at Typology.

However, MBBT is extremely hydrophobic, with an estimated log P of 12.7, and has a very low water solubility, less than 5 ng/L. These properties account for its strong persistence in the environment. Indeed, when it is rinsed into water, for instance at the beach, MBBT tends to accumulate in sediments and aquatic organisms, thereby posing potential risks to marine ecosystems. Traces have been found in shellfish, fish, and crustaceans, suggesting a potential for bioaccumulation. Furthermore, MBBT is not biodegradable, another harmful characteristic if it ends up in the environment.

The nano form of MBBT still raises concerns.

As mentioned above, MBBT is often used in nanometric form. However, unlike the non-nano form, according to the CSSC, data on its genotoxicity remains insufficient. To remind, the genotoxicity of a substance refers to its ability to damage the DNA of a living organism. The genotoxic character of a compound is generally a good indication of its cancer-causing potential. At the moment, the committee has not been able to firmly rule on the safety of the nano form of MBBT due to the lack of currently available data. Tests in vitro on animal cell lines have not shown a clear genotoxic effect, but the results have not been conclusive enough for the CSSC to declare a lack of danger.

Inhalation tests were also conducted by the CSSC, demonstrating an absence of acute pulmonary toxicity at 0.488 mg/L with respirable particles of 1.4 µm. Despite this, the committee recommends not using the nano form in spray or loose powder formulations, due to the lack of long-term data on respiratory toxicity. This caution is all the more justified as nanometre-sized particles could theoretically reach the lung alveoli, potentially leading to entry into the bloodstream and potentially harmful effects on tissues.

MBBT is suspected to be irritating to the skin.

Several studies conducted on animals have investigated the acute, subchronic toxicity and local effects of MBBT. When applied daily to rats for several weeks at high doses (up to 2,000 mg/kg/day), MBBT did not cause any notable systemic or organic adverse effects. However, from a local tolerance perspective, the picture remains unclear. Indeed, tests were conducted on mice to which 20% MBBT was applied. A few isolated cases of skin allergy were reported, as well as the formation of scabs. Although the concentration used is twice the amount permitted in skincare products, the CSSC concluded that it would be "useful to monitor possible irritation effects via the programmes of cosmetovigilance".

That’s why we don’t use MBBT in our solar products. Despite its UV protection effectiveness, its toxicological uncertainties, environmental impact and local irritant potential have led us to prefer better documented UV filters.