Harvard researchers found that nearly 16 percent of the test participants suffered from endocrine dysfunction in connection with PFAS exposure.
A new study published in JAMA Network Open has found that exposure to perfluoroalkyl and polyfluoroalkyl substances-commonly referred to as PFAS, or “forever chemicals”-is linked to significantly higher rates of endocrine disruption among American women.
The study, conducted by the lead researcher Rezaul Karim Ripon from Harvard T.H. Chan School of Public Health, used data from nearly 2,000 women to find that those with higher levels of certain PFAS compounds in their blood were substantially more likely to experience hormonal imbalances requiring treatment with estrogen or progesterone.
Widespread Exposure, Growing Concern
PFAS are man-made chemicals in a family of compounds that have been used in everything from non-stick cookware to water-resistant clothing and food packaging. Their extreme durability has made them omnipresent in the environment—and in human bodies. Nearly everyone in the United States has detectable levels of PFAS in their blood, according to researchers, mostly through contaminated drinking water, food, and household dust.
These chemicals are everywhere, and they’re not going away, the study notes, highlighting that PFAS contamination is here to stay.
Key Findings
The study tested for seven different PFAS compounds in blood samples of women aged 31 to 74 years. Of the total 1,995 participants in the study, 15.8% showed signs of endocrine disruption, indicated by their need for hormone replacement therapy.
The results showed striking patterns:
- In women with endocrine disruption, significantly higher concentrations of several PFAS compounds were found, especially n-PFOS, PFNA, and PFOA.
- Among these compounds, n-PFOS had the strongest association, with estimates over threefold higher than those for other types of PFAS.
- When looking at exposure to multiple PFAS chemicals in combination, the odds of endocrine disruption for women in the highest exposed category (75th percentile) were found to be 82% higher than for women in the lower exposed category (25th percentile).
Sm-PFOS was revealed as the major driver in the mixture, responsible for most of the magnitude of the effects observed.
The Cocktail Effect
What makes this research particularly significant is that, for the first time, it examines mixtures of PFAS, rather than evaluating individual chemicals in isolation. Using a sophisticated statistical technique called Bayesian kernel machine regression, the team was able to show that exposure to mixtures of these chemicals increases health risks.
The researchers found: “Exposure to mixtures of PFAS remained positively associated with developing endocrine disruption,” suggesting that the real-world scenario of multiple chemical exposures may pose greater health threats than previously understood.
How PFAS Disrupt Hormones
The study provides a potential mechanism for how these chemicals interfere with normal hormone function. PFAS molecules structurally resemble fatty acids, which enables them to interfere with the proteins responsible for the transport of hormones, mainly those of thyroid hormones. This could provide a molecular explanation for the high efficiency of these chemicals in disrupting the body’s sensitive endocrine system.
Previous studies have indicated that PFAS can alter lipid metabolism, amino acid processing, and thyroid hormone function-all integral parts of the endocrine system.
Who’s Most Affected
The present study also found that women with endocrine disruption were more likely to be older and non-Hispanic White; the median age of affected women was 67 years, while in women without disruption, it was 45 years. Higher concentrations of several PFAS compounds were consistently found in the affected group.
Limitations and Next Steps
The researchers acknowledge several important limitations: The cross-sectional design of the study does not allow for a causal relationship to be established between PFAS exposure and endocrine disruption, and vice versa.
In addition, the definition of endocrine disruption here, based on hormone replacement therapy use, may not capture all cases of hormonal dysfunction and may include, for example, women taking hormones for menopausal symptom management or for the prevention of osteoporosis.
Public Health Implications
These findings emphasize the urgent need for regulatory action and public health interventions in light of widespread and persistent environmental contamination with PFAS. Their persistence ensures that exposures building up today will persist both in the environment and in human bodies for decades to come.
As ongoing research unravels the health ramifications of these omnipresent chemicals, the study joins a growing body of proof that ties PFAS to major health concerns, spanning from cancer and immune system dysfunction to reproductive and developmental problems. The research team thus calls for further investigation into the long-term effects of PFAS mixtures and emphasizes the importance of reducing exposure through contamination prevention and remediation efforts. The study was published in JAMA Network Open on December 5, 2025, and examined data from the National Health and Nutrition Examination Survey collected between the years 2015 and 2020.
Published: December 8, 2025 doi:10.1001/jamanetworkopen.2025.39425
