In-depth guide

UPDATED FEB 2026

AFFF Thyroid Disease Lawsuit

Part of the AFFF Firefighting Foam investigation

The short answer

Thyroid disease is one of six conditions with a C8 Science Panel "probable link" to PFOA exposure. PFAS are potent endocrine disruptors that interfere with thyroid hormone synthesis and metabolism, causing hypothyroidism, hyperthyroidism, and thyroid cancer.

Thyroid disease is often the earliest clinical manifestation of PFAS exposure and may affect a broader population than PFAS-linked cancers, making it significant for the AFFF litigation.

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PFAS and Thyroid Disease: Endocrine Disruption

The thyroid gland is one of the organs most sensitive to PFAS exposure. Per- and polyfluoroalkyl substances are classified as endocrine disruptors — chemicals that interfere with the body's hormonal signaling systems. PFAS specifically target the thyroid by competing with thyroid hormones (T3 and T4) for binding sites on transport proteins, disrupting the hypothalamic-pituitary-thyroid axis, and altering circulating hormone levels. These effects can cause the full spectrum of thyroid disease: hypothyroidism, hyperthyroidism, autoimmune thyroiditis, thyroid nodules, and thyroid cancer.

The C8 Science Panel determined a "probable link" between PFOA exposure and thyroid disease based on the 69,000-person Mid-Ohio Valley study. Residents with higher PFOA blood levels had significantly elevated rates of thyroid dysfunction. Subsequent studies have confirmed the association across multiple populations, including firefighters, military personnel, and communities with PFAS-contaminated drinking water. The consistency of findings across diverse populations strengthens the causal inference.

Thyroid disease may affect a broader population of PFAS-exposed individuals than cancers because the endocrine-disrupting effects of PFAS occur at lower exposure levels than the carcinogenic effects. This means that individuals whose PFAS exposure was not sufficient to cause cancer may still develop thyroid disease. For the AFFF litigation, thyroid disease claims represent a significant portion of the total case volume because the condition is more common than kidney or testicular cancer.

Thyroid Disease Symptoms and Diagnosis

Hypothyroidism — the most common thyroid condition linked to PFAS exposure — causes fatigue, weight gain, cold intolerance, constipation, dry skin, depression, and difficulty concentrating. Hyperthyroidism causes weight loss, rapid heartbeat, anxiety, tremor, heat intolerance, and insomnia. Both conditions are diagnosed through blood tests measuring thyroid-stimulating hormone (TSH), free T4, and free T3 levels. Thyroid antibody testing can identify autoimmune thyroiditis (Hashimoto's disease).

Thyroid cancer — while less common than functional thyroid disease — is a more serious diagnosis that may also be linked to PFAS exposure. Papillary thyroid carcinoma, the most common subtype, has been associated with PFAS exposure in several studies. Thyroid cancer is typically detected as a nodule on physical examination or incidentally on imaging studies, and diagnosed through fine needle aspiration biopsy. Treatment involves thyroidectomy, radioactive iodine therapy, and lifelong thyroid hormone replacement.

Individuals with AFFF exposure who have been diagnosed with any form of thyroid disease should consult both their endocrinologist and an AFFF attorney. The combination of the C8 Science Panel "probable link" determination and the well-understood endocrine-disrupting mechanism of PFAS provides a strong foundation for thyroid disease claims in MDL 2873.

Research & evidence

Scientific Evidence

meta-analysis

Meta-Analysis of PFAS Exposure and Cancer Risk: Kidney and Testicular Cancer

Mastrantonio M, Bai E, Uccelli R, Cordiano V, Screpanti A, Corigliano P. (2023). La Medicina del Lavoro

Key findings

  • Relative risk of 1.74 for kidney cancer among individuals with high PFAS exposure compared to low-exposure controls
  • Relative risk of 2.22 for testicular cancer among individuals with high PFAS exposure — the strongest relative risk of any PFAS-cancer association
  • Dose-response relationship demonstrated: higher PFAS blood levels correlated with progressively higher cancer risk
  • Results consistent across multiple study designs and populations, strengthening the causal inference
retrospective

"The Devil They Knew": Industry Knowledge of PFAS Dangers Since 1970

Brennan NM, Evans AT, Fritz MK, Peak SA, von Holst HE. (2023). Annals of Global Health

Key findings

  • PFAS manufacturers knew about the persistence and toxicity of their products as early as 1970 — more than 50 years before widespread public awareness
  • 3M conducted internal studies showing PFAS bioaccumulation in worker blood at 1,000 times normal levels and animal studies showing tumor formation, then classified results as confidential
  • Manufacturers used trade secret protections and proprietary research agreements to prevent damaging findings from reaching regulators or the public
  • The pattern of corporate concealment parallels the tobacco and asbestos industries and supports punitive damages claims based on willful and malicious conduct
cohort

C8 Science Panel: Probable Link Evaluations for PFOA-Associated Diseases

Fletcher T, Savitz D, Steenland K. (2012). Environmental Health Perspectives

Key findings

  • Determined "probable link" between PFOA exposure and six diseases: kidney cancer, testicular cancer, thyroid disease, ulcerative colitis, high cholesterol, and pregnancy-induced hypertension
  • Study population of 69,000 residents made it one of the largest PFAS health studies ever conducted, providing exceptional statistical power
  • Findings have been cited in virtually every subsequent PFAS lawsuit and regulatory action worldwide
  • The "probable link" standard — requiring more than just association but less than definitive proof — was a negotiated scientific threshold that has become the benchmark for PFAS causation evidence

FAQ

Frequently Asked Questions

36 QUESTIONS

The primary categories of eligible plaintiffs include: firefighters (municipal, airport, military, or industrial) who handled AFFF during training or fire suppression; military personnel stationed at bases where AFFF was used or stored (the DoD has identified 455+ contaminated installations); military families who lived on or near contaminated bases; community residents whose drinking water was contaminated by PFAS from nearby military bases, airports, or fire training facilities; and industrial workers at PFAS manufacturing plants. Linked conditions include kidney cancer, testicular cancer, thyroid disease, ulcerative colitis, liver damage, non-Hodgkin lymphoma, and high cholesterol. Attorneys handle these cases on contingency — fee terms vary by attorney.

Dive deeper

Related Guides

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The full investigation

Part of the AFFF Firefighting Foam Investigation