A "Safer" PFAS Replacement Is Disrupting Thyroid Hormones

The chemicals replacing old PFAS aren't any safer. A newer PFAS alternative called Cl-PFESA is disrupting thyroid hormone production in human cells at levels found in children's blood.

Thyroid Hormones Went Haywire

Researchers exposed human thyroid cells to Cl-PFESA (chlorinated polyfluoroether sulfonate) at concentrations matching what's actually found in kids' blood. The cells started overproducing T3 and T4 thyroid hormones, according to a 2026 study in Toxicology.

That's the opposite of what animal studies predicted. In lab animals, PFAS typically suppresses thyroid function. But in human thyroid cells, Cl-PFESA activated a gene called PAX8 that cranked up the hormone-making machinery.

Iodine Made It Unpredictable

When researchers added iodide (the form of iodine your thyroid uses), the effects weren't straightforward. Low iodide boosted the disruption. Higher levels partially suppressed it. This means your iodine intake could make Cl-PFESA exposure better or worse in ways nobody is monitoring.

Cl-PFESA was introduced as a "safer" replacement for older PFAS chemicals. It's already showing up in human blood, including children.

What You Can Do

Avoid products marketed as stain-resistant or waterproof. Filter drinking water. Skip greaseproof food wrappers. And explore non-toxic home essentials to reduce your family's PFAS exposure from everyday products.

Also see non-toxic kitchen essentials for safer alternatives.

Source: Teng M, Zhuang J, Yang L, et al. (2026). Toxicology.