What you should know about 'forever chemicals' and their impact on health

Invisible, omnipresent "forever chemicals" have been linked to a wide range of serious effects on human health, prompting growing calls for them to be banned. While there is firm evidence that at least one of the more than 4,000 human-made chemicals called PFAS causes cancer, researchers are still attempting to fully understand their broader impact on health.

Here is what we know so far.

What are PFAS?

Per- and polyfluoroalkyl substances (PFAS) are synthetic chemicals first developed in the 1940s to withstand intense heat and repel water and grease.

Ever since, they have been used in a wide range of household and industrial products including food packaging, make-up, stain-proof fabric, non-stick pots and pans and foam used to fight fires.

Because PFASs take an extremely long time to break down — earning them the nickname "forever chemicals" — over the years they have leached into the soil and groundwater, entering our food chain and drinking water.

These chemicals have now been detected virtually everywhere on Earth, from the top of Mount Everest to inside human blood and brains.

Two biggest culprits

The two most researched PFAS compounds have already been banned or restricted in many countries, though they remain detectable throughout the environment.

Perfluorooctanoic acid (PFOA), which was once used to make the non-stick cookware coating Teflon, was in December classified as "carcinogenic to humans" by the International Agency for Research on Cancer (IARC).

The World Health Organization agency said there is "sufficient evidence" that PFOA gave animals cancer during experiments, as well as "limited evidence" of renal cell and testicular cancer in humans.

Perfluorooctane sulfonic acid (PFOS) — once the key ingredient in the Scotchgard fabric protector — was meanwhile ruled "possibly carcinogenic to humans".

There was limited proof of cancer in animals but "inadequate evidence regarding cancer in humans", the IARC said.

Other linked diseases

More broadly, observational studies indicate that exposure to PFAS chemicals correlates with elevated risks of cancer, obesity, thyroid, liver, and kidney diseases, as well as higher cholesterol levels, low birth weight, infertility, and potentially diminished response to vaccines.

However, such observational research cannot prove that the chemicals directly cause these health problems.

The level of risk can vary greatly depending on the level of PFAS people are exposed to — almost everyone on Earth is believed to have at least a little PFAS in their bodies.

According to the IARC, those most at risk of significant PFAS exposure are individuals who handle the chemicals directly during the manufacturing of products.

Question of Exposure

The exact level of PFAS exposure that is considered harmful to health has been debated.

Previously, guidelines in many countries suggested that less than 100 nanograms of PFAS per litre of tap water was sufficient to protect health.

However, the US has proposed lowering the limit to four nanogrammes of PFOA and PFOS per litre — and the EU is considering following suit.

Last year, a media investigation found PFAS levels over 100 nanogrammes per litre at 2,100 sites across Europe and the UK.

The level soared over 10,000 nanogrammes at 300 of the sites, according to the investigation carried out by 16 newsrooms.

Chemical whack-a-mole

Further complicating the ability of research to comprehend the health effects of PFAS is that new compounds are still being developed.

Researchers have cautioned that as manufacturers phase out compounds identified as potentially hazardous, they often substitute them with another member of the PFAS family that has undergone less scrutiny.

Harvard environmental researcher Elsie Sunderland has called this process "chemical whack-a-mole".

Calls for action

Environmentalists and health experts across the world have been increasingly sounding the alarm about forever chemicals.

French MP Nicolas Thierry will introduce a bill that — if passed — would ban non-essential PFAS in France from 2025.

The European Union is also considering a Europe-wide ban on PFAS from as early as 2026.

What can you do?

For people at home, it is nearly impossible to avoid consuming minuscule amounts of PFAS.

However, experts recommend reducing contact with non-stick cookware and grease-proof food packaging such as fast food wrappers.

Drinking filtered or bottled water and storing leftovers in glass -- not plastic -- containers could also help.