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PFAS and cancer: what do we know about forever chemicals?

by Tim Gunn , Sophie Brooks | News

11 December 2023

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The International Agency for Research on Cancer's (IARC's) website, seen on a phone and a computer.
The International Agency for Research on Cancer (IARC) is part of the World Health Organization (WHO). T. Schneider/

The International Agency for Research on Cancer (IARC) has finalised its evaluation of possible links between two ‘forever chemicals’ and cancer in humans. 

Forever chemicals, known to scientists as poly and perfluoroalkyl substances (PFAS), are a group of thousands of man-made chemicals used for manufacturing and in various everyday products.  

They’re nicknamed forever chemicals because the special chemical structures that make them so useful are also extremely difficult to break down. As a result, PFAS can stick around long after people have finished with them. They can also enter the surrounding environment, which means we can encounter them without knowing it. 

The two chemicals IARC looked at are no longer produced or used in the UK. IARC has now classified one of them, perfluorooctanoic acid (PFOA), as cancer-causing, or carcinogenic (Group 1), but this decision wasn’t based on strong evidence showing an increase in cancer cases in people exposed to PFOA.

Instead, IARC noted ‘sufficient’ evidence for PFOA-linked cancers in one species of experimental (lab) animal. They also found ‘strong’ evidence that PFOA can cause changes in the human body that may lead to the development of cancer. 

When looking specifically at cancer cases in humans exposed to PFOA, IARC only found ‘limited’ evidence of a direct link to renal cell carcinoma and testicular cancer. For all other cancer types, IARC’s committee considered the evidence for a direct link ‘inadequate’. 

The other chemical IARC reviewed, perfluorooctanesulfonic acid (PFOS), has been classified as ‘possibly carcinogenic to humans’ (Group 2B). This decision was also based on ‘strong’ evidence that PFOS may cause changes within our body that could be linked to cancer.  

But, in this case, IARC noted that there was ‘inadequate’ evidence that PFOS directly causes any type of cancer in people. The evidence in experimental animals was also ‘limited’. Overall, this suggests there is currently no convincing evidence that PFOS causes cancer in humans.  

How does IARC’s classification system work? 

IARC’s classification system reflects whether something has the potential to cause cancer (its ‘hazard’), but it doesn’t tell us how dangerous that thing is (its level of risk).  

By classifying PFOA as Group 1, IARC is saying that, overall, scientific evidence suggests it has the potential to cause cancer. That doesn’t mean it poses the same level of risk as other things in the group. Active smoking, second-hand smoke and air pollution are all in Group 1 as well, but they come with very different levels of risk. 

And, even though PFOA is classified as something that can cause cancer, the level of risk it poses to people depends on many things that are still being investigated, including our level of exposure and its potential interaction with other chemicals.  

PFOS is now in Group 2B, meaning the evidence on the potential for it to cause cancer is still inconclusive. This is the same category as things like aloe vera and bracken ferns, but, again, this doesn’t tell us the level of risk (if there is one). 

Studying PFAS 

It’s difficult to study the specific health effects of forever chemicals like PFOA and PFOS might have on people, and at what level of exposure they might pose a problem.  

Although animal studies let scientists test the effect of individual substances on living models, they don’t completely match the human body. It’s also common for these studies to use exposure levels far higher than those that people experience.  

The limited human studies into PFAS and cancer are affected by other factors, like people’s genetics, lifestyles and exposure to different chemicals. That makes it difficult to draw a definitive link.  

But we are learning more. After reviewing new studies, IARC moved PFOA from Group 2B (possibly carcinogenic) to Group 1 (carcinogenic). The evidence that PFOA can cause cancer still isn’t as strong as the evidence we have for some other things classified in Group 1, but the change shows just how important research is for understanding cancer risk. It’s essential more research is done to help improve our understanding of these chemicals and their health impacts. 

Where are these forever chemicals? What can we do about them? 

It’s now illegal to use PFOA or PFOS in the UK, but we’re still living with them. Before regulations were put in place in the 2000s, PFOA and PFOS were used in packaging, carpets, cookware, manufacturing processes, firefighting foams and waterproof clothing. Even though those products and processes might not exist anymore, the chemicals they contained still may not have broken down. 

The fact forever chemicals are so long-lasting also means they can filter out into the environment. That makes it difficult for individual people to avoid them. Because of that, effective monitoring is important for us to understand whether and which measures may be needed to reduce any potential risk – from PFOA, PFOS or any similar chemical.  

Researchers are still looking into PFOA and PFOS, but there are proven ways to reduce the risk of cancer. Visit our causes of cancer page for more information.