Could nail varnishes be a source of exposure to endocrine disruptors?

According to the World Health Organisation (WHO), an endocrine disruptor is "a substance or mixture of substances that alters the functions of the endocrine system and consequently induces harmful effects in an intact organism, its offspring, or within sub-populations".

In simpler terms, it refers to a family of compounds capable of interacting with the hormonal system, thus affecting various bodily functions (metabolism, nervous system, reproductive functions). Endocrine disruptors can, for example, interact with the synthesis, transport, mode of action or even the degradation of hormones. Most often, these substances alter the natural production of intrinsic hormones, mimic the action of these hormones by substituting for them or prevent their action by attaching to the receptors with which they usually interact. Exposure to endocrine disruptors is particularly problematic for pregnant women and young children, whose endocrine system is highly vulnerable to chemical alterations. Unfortunately, endocrine disruptors are ubiquitous in our daily lives and can even be hidden in certain skincare products.

Several studies have shown that certain compounds found in many nail varnishes could interfere with the hormonal system. Among the problematic molecules, phthalates are found, particularly dibutyl phthalate (DBP), which was once widely used to soften varnishes and prevent them from chipping too quickly. Dibutyl phthalate is now banned in the European Union due to its proven impact on the reproductive system. Research has shown that it can alter testosterone production in men and accelerate the onset of puberty in women.

Despite the removal of DBP from nail varnishes, concern remains.

Indeed, dibutyl phthalate was not the only problematic ingredient in nail varnishes. Parabens, often found in nail varnishes as preservatives , are also suspected to be endocrine disruptors. These molecules could potentially mimic the action of oestrogens and bind to receptors specific to these hormones, thereby activating them. Consequently, parabens raise questions about their impact on fertility and their role in the occurrence of hormone-dependent cancers, such as breast cancer. Studies conducted on rodents report effects of parabens on male and female reproductive systems, but other studies conducted on humans do not show an association between urinary paraben concentrations and circulating hormone levels or sperm quality. The epidemiological studies available to date are still too few to assert that parabens are endocrine disruptors, but certain elements suggest caution.

Another ingredient often implicated in nail varnishes is triphenyl phosphate (TPHP). This molecule, also used in inks and paints, is suspected of interacting with and disrupting the hormonal system. Data on its toxicity in humans is scarce, but studies conducted on animals raise concerns. For instance, it has been shown that short-term exposure (21 days) to triphenyl phosphate in zebrafish was associated with a disruption of the balance of sexual hormones and reproductive function. Even though TPHP is not a proven endocrine disruptor, it remains a concern, especially considering that, according to the international Skin Deep database, managed by the Environmental Working Group and listing more than 27,000 cosmetics, TPHP was listed on the label of about one in two nail varnishes available for sale between 2012 and 2015.

A recent study sought to assess whether the application of nail varnish could potentially expose individuals to TPHP. To do this, urinary levels of diphenyl phosphate (DPHP), a primary metabolite of TPHP, were measured before and after the application of a TPHP-containing varnish on nails or gloves. This was done to determine whether TPHP was absorbed through the skin or inhaled. The results revealed a significant increase in urinary DPHP levels after applying the varnish directly to the nails, as opposed to applying it on gloves, suggesting a predominantly dermal absorption of TPHP. While further research is still needed to confirm the potential dangers of TPHP and its potential role as an endocrine disruptor, these findings highlight the importance of remaining vigilant about its use.