Are PFAS ‘Forever Chemicals’ Causing Thyroid Cancer?

Looking at the science behind the headlines

Gideon M-K; Health Nerd


Pictured: Some PFAS, probably. Photo by Markus Spiske on Unsplash

PFAS — the collective acronym for per- and polyfluoroalkyl substances — are something that we love to hate. They are a class of chemicals used in a lot of industrial applications, such as clothing and plastics, because they have a bunch of useful qualities. They are also increasingly the focus of epidemiological research, because there are concerns about whether PFAS could be causing a range of human health issues.

In addition, PFAS are somewhat worrying because they take a long time to break down in the environment. This has lead the media to dub them ‘forever chemicals’. And, according to recent headlines, these forever chemicals might be giving people thyroid cancer.

This was the first image that came up in a search for “thyroid”, which I guess is both technically correct and a bit confusing. Photo by Taylor Deas-Melesh on Unsplash

Fortunately for all of us, the link between PFAS and thyroid cancer is, at best, incredibly weak. While it’s not impossible that PFAS substances might be causing issues with your thyroid, the evidence thus far is unconvincing and probably not worth worrying about.

The Science

The headlines that have sprung up everywhere about PFAS are based on a new epidemiological investigation published recently in the journal eBioMedicine, an offshoot of the prestigious journal the Lancet. In this study, researchers took a group of people with thyroid cancer who’d had a range of blood tests before their diagnosis, and compared them to some matched controls who had blood tests but no thyroid cancer.

After controlling for a number of factors, the researchers found that for one PFAS, specifically n-PFOS, there was a modest correlation with thyroid cancer. The corrected odds ratio for this association was 1.56, which means that the odds of having thyroid cancer were increased by 56% for people with much higher levels of this substance in their blood.

This finding has led to the many headlines about PFAS causing cancer, but I think it’s worth putting the results into proper context before getting terrified about this all-new cancer risk. Firstly, this study was genuinely tiny — the authors…