Waterproof mascara that doesn’t run. Foundation that stays put. For many women, long-wear make-up is a welcome convenience.

Yet the reason many of these products cling so firmly to the skin is because of so-called ‘forever chemicals’ known as PFAS, (per- and polyfluoroalkyl substances).

This is a family of 10,000 ­manmade chemicals designed to produce ­surfaces that are smooth, glossy and water-resistant.

But increasingly, concerns are being raised that these chemicals are linked to hormone disruption, a weaker immune system and even some cancers.

Now France is to become the first country to ban PFAS from all cosmetics, textiles and waxed products (such as ski wax)­­­­ from January.

In the UK, the Health and Safety Executive completed a review of PFAS in 2023, but ministers are still to decide whether to ban or restrict them (according to an answer to a parliamentary question in May).

PFAS are found everywhere, from tap water to house dust, and in the blood of every human, according to the UN Environment Programme and the US Centers for Disease Control.

PFAS have chemical bonds that are virtually indestructible, meaning they can take ­centuries to break down and ­disappear – hence the moniker ‘forever’ chemicals.

The problem, say scientists, is that their durability in products means durability inside the body, too. This is why there are concerns about their use in make-up.

PFAS molecules stick to proteins in the blood, where they can interfere with hormones and the immune system.

One PFAS commonly used in make-up, for example, is PTFE, which creates a silky texture and helps it cling to lashes or skin for a flawless, waterproof finish.

‘PFAS are highly persistent, and for several of them the ­evidence for toxicity is strong,’ says Professor Miriam ­Diamond, an environmental chemist at the University of Toronto, and author of a major 2021 study that suggested PFAS were present in more than half of tested cosmetics.

‘If PFAS get into the eye, the tear duct is a very efficient route into the body. Eyelid skin is thin and permeable,’ she says. ‘And when it comes to ­lipstick, a woman can easily swallow several pounds of ­lipstick in her lifetime.’

A review in Environment International in 2024 reported that ­forever chemicals can get through the skin and enter the bloodstream, especially from products applied repeatedly to thin skin (such as older people’s) or skin damaged by conditions such as eczema, sun exposure or exfoliants.

Professor Diamond says this matters because some of the strongest human evidence links PFAS exposure to weaker immune systems.

‘People with higher PFAS ­levels in their blood show weaker vaccine responses and lower antibody production,’ she explains. A 2023 study in the journal Environmental Health ­Perspectives found adults with higher PFAS exposure produced significantly weaker antibody responses after Covid-19 vaccination.

Professor Diamond adds: ‘Other studies show changes in fat and sugar metabolism that raise diabetes risk.’

A 2022 study in the journal Toxics found that people with higher levels of PFAS in their blood were more likely to develop insulin resistance and type 2 diabetes.

‘The prudent thing is to stop using PFAS in cosmetics as it’s not necessary,’ argues Professor Diamond.

PFAS come in many forms, but most fall into two groups: long chain and short chain.

The older, long-chain types – such as PFOA and PFOS – have been banned in several countries, including the UK, after being linked to cancer and other health problems.

These have largely been replaced in consumer goods, including make-up, by short-chain PFAS, which are thought to break down more quickly in the environment.

But scientists now warn that these newer versions – including those found in some ­cosmetics – may travel further through the body because they’re smaller molecules and prove just as harmful, if not more so, in the long run.

Professor Graham Peaslee, an environmental scientist at the University of Notre Dame in the US, has spent more than a decade studying how PFAS move through the body. He says short-chain versions may be even more concerning than the older ones, not least because manufacturers ‘must use more of the short-chain chemicals to do the same job as the older ones, and because they’re more water-soluble they get out into the environment even faster’.

He adds short-chain PFAS also move through the skin more easily and enter the body in greater amounts.

A 2022 study by the ­University of Birmingham found that up to 50 per cent of applied PFAS could pass through human skin within 24 hours.

Early lab studies suggest that once inside the body, PFAS can cross the blood-brain barrier – the defence that normally stops most chemicals reaching brain tissue, raising concerns they could interfere with brain chemistry or nerve function. But more research is needed.

A spokesperson for the Cosmetic, Toiletry and Perfumery Association said cosmetics are already covered by strict safety laws and that a voluntary Europe-wide phase-out of PFAS is in progress.

‘Shoppers shouldn’t have to play detective to avoid harmful ingredients,’ says Anna ­Watson, head of policy and advocacy at Chem Trust, a charity ­campaigning for tougher regulations for harmful chemicals.

‘These forever chemicals must be banned to truly ­protect our health and the environment,’ she adds.

Until then, Professor Peaslee says the simplest fix lies with shoppers: ‘If we all choose the PFAS-free options, there will be no demand for the ones made with toxic chemicals.’

To identify if a product ­contains these, look for PTFE, perfluorononyl dimethicone, perfluorodecalin, or words beginning ‘perfluoro-’ or ‘polyfluoro-’ on the label.