Research on the health harms of PFAS is widely available for many long-chain PFAS, with much of the focus on PFOA and PFOS.

Increasing research indicates PFAS demonstrates the potential for harm across endocrine, neurological, respiratory, immune, urinary, gastrointestinal, reproductive, and cardiovascular systems.

The following specific conditions have been studied in relation to general PFAS exposure:

• Asthma: There is limited evidence that in utero and early life exposure to PFAS increases the risk of infections, allergies, asthma, and atopic dermatitis.
• Cancer: The International Agency for Research on Cancer (IARC) classified perfluorooctanoic acid, PFOA, a legacy PFAS, as a possible human carcinogen. The most evidence-based associations with PFOA and cancer are for kidney and testicular cancer. There are also associations in the literature between PFAS and prostate cancer.
• Diabetes: Studies show PFAS appear to behave as potential diabetogens. They can affect PPAR (peroxisome proliferator-activated) receptors that regulate adipocyte differentiation and lipid and glucose homeostasis.
• Hyperlipidemia: Numerous studies show a positive association between elevated PFAS levels and serum lipids, notably LDL and total cholesterol.
• Male infertility: Preclinical studies and epidemiological studies suggest PFAS exposure affects testosterone levels and semen quality, potentially due to toxicity to Leydig cells and changes in levels of steroidogenic enzymes.
• Female infertility: Studies suggest that PFAS, found in follicular fluid, may contribute to fertility issues and affect oocyte development.
• Kidney Disease: Numerous epidemiological studies report an association between exposure to PFAS and reduced kidney function or kidney cancer. Toxicology studies demonstrate structural alterations in the proximal tubules of the nephron and dysregulated metabolic pathways, amongst other mechanisms.
• Liver Disease: Several epidemiological studies report an association between increased PFOA and elevated transaminases. Additional studies on multiple PFAS report changes in liver biomarkers, including transaminases, bilirubin, and GGT.
• Lower infant birth rate: Low birth weight is a consistently reported adverse pregnancy outcome in epidemiological and animal studies relating to gestational PFAS exposure. Studies have found this result in PFOA and several other legacy PFAS.
• Obesity: At least 15 studies have reported positive associations between overweight or obesity and the exposure to at least one PFAS. The studies span many geographic regions and diverse age groups, including maternal exposure and childhood obesity, as well as adults. Mechanisms underlying this may relate to altered leptin levels and other metabolic dysregulations.
• Pre-eclampsia: Several epidemiologic studies have found positive associations between maternal exposure to PFAS and pre-eclampsia. Some research suggests this is related to the impairment of placental function, though the exact mechanism has yet to be fully elucidated.
• Thyroid disease: Studies have found associations with elevated PFOS and PFOA, an increased risk of thyroid disease, and associated alterations in TSH and thyroid hormone levels. In vitro and animal studies support a thyroid-disrupting effect of both old and new-generation PFAS.
• Ulcerative Colitis: PFOA has been shown to have a significant, positive association with ulcerative colitis in highly exposed individuals, though mechanisms remain unclear.