Are PFAS forever chemicals harmful to your health?

The health effects of PFAS have been studied extensively since the early 2000s, particularly through the C8 Health Project -- one of the largest epidemiological studies ever conducted -- which tracked nearly 70,000 people living near a DuPont PFOA-manufacturing plant in West Virginia.

Cancer: The C8 study and IARC (International Agency for Research on Cancer) have established probable links between PFOA exposure and kidney cancer and testicular cancer. In 2023, IARC classified PFOA as a Group 1 carcinogen (carcinogenic to humans) and PFOS as a Group 2B carcinogen (possibly carcinogenic).

Thyroid disruption: PFAS interfere with thyroid hormone synthesis and transport. Multiple epidemiological studies have found associations between higher PFAS blood levels and thyroid disease, particularly hypothyroidism in women¹. This is concerning because thyroid hormones are critical for metabolism and fetal brain development.

Immune suppression: PFAS exposure reduces antibody responses to vaccines in both children and adults. The NTP concluded in 2016 that PFOA and PFOS are "presumed to be an immune hazard to humans" based on consistent evidence from human and animal studies⁵.

Metabolic effects: A JAMA Network Open study found that higher PFAS blood levels were associated with greater weight regain after dieting, potentially through suppression of resting metabolic rate².

Reproductive health: PFAS exposure during pregnancy has been linked to preeclampsia, reduced birth weight, and developmental effects in children.

The evidence base for PFAS health effects has strengthened considerably over the past decade. Key findings from the peer-reviewed literature:

Cancer mechanisms and epidemiology: PFOA's 2023 IARC Group 1 classification was based on "sufficient evidence" in humans for kidney cancer, with mechanistic evidence including epigenetic alterations, oxidative stress, immunosuppression, and receptor-mediated effects. The C8 study found a dose-response relationship between PFOA serum levels and kidney cancer incidence. Testicular cancer risk was elevated with odds ratios of 1.3-3.0 in occupational cohorts, with stronger associations at higher cumulative exposures.

Thyroid pathophysiology: PFAS compete with thyroid hormones (T3 and T4) for binding to transport proteins such as transthyretin and thyroid-binding globulin¹. In vitro studies demonstrate direct inhibition of the sodium-iodide symporter and thyroid peroxidase. Population studies consistently show associations between PFAS quartiles and TSH elevation, particularly in women of reproductive age. Prenatal PFAS exposure has been associated with altered thyroid hormone levels in neonates, raising concerns about neurodevelopmental impacts.

Immunotoxicity dose-response: The NTP systematic review graded the evidence as "high" confidence for immunosuppression in humans⁵. These immune effects occur at background exposure levels found in the general population, suggesting there may be no safe threshold.

Metabolic disruption: The JAMA Network Open study by Liu et al. followed 621 overweight or obese participants over two years². Those in the highest tertile of baseline PFAS levels regained an average of 2.4 kg more weight than those in the lowest tertile, with the association strongest for PFOS. The mechanism appears to involve PPAR-alpha activation and disruption of lipid and energy metabolism. Elevated total cholesterol is one of the most consistently replicated findings across PFAS epidemiological studies, with effects observed at serum PFOA levels as low as 2 ng/mL.

Reproductive and developmental toxicity: A meta-analysis of 24 studies found that each 1 ng/mL increase in maternal PFOA was associated with an 18.9 g decrease in birth weight. Animal studies demonstrate PFAS-induced disruption of estrogen, androgen, and progesterone signaling, with human data showing associations between PFAS exposure and longer time-to-pregnancy, endometriosis, and polycystic ovary syndrome.