Can chlorinated tap water chemicals disrupt your thyroid?
Yes. Mixed exposure to trihalomethanes and haloacetic acids from chlorinated tap water was linked to altered thyroid hormone levels.
What's actually in it
When chlorine disinfects tap water, it reacts with organic matter to create trihalomethanes (THMs) and haloacetic acids (HAAs). You absorb these byproducts by drinking the water, showering in it, and breathing steam from hot water. The exposure is daily and lifelong.
Your thyroid gland is sensitive to halogenated chemicals because they resemble iodine, the element your thyroid uses to make hormones. THMs and HAAs can interfere with this process.
What the research says
A 2026 study in Environ Sci Technol measured urinary THMs and HAAs in adults and tested how the combined exposure affected thyroid function.
People with higher combined levels of these chlorination byproducts had altered thyroid hormone levels. The effects were stronger when multiple byproducts were present together, suggesting the chemicals work as a mixture.
The thyroid changes included shifts in T3, T4, and TSH that could affect metabolism, energy, and body weight. Even modest thyroid disruption can cause fatigue, weight changes, and mood problems.
Using a carbon filter on your drinking water and kitchen faucet removes most chlorination byproducts. Shorter showers and better bathroom ventilation reduce exposure from steam.
The research at a glance
| Study | Journal | Year |
|---|---|---|
| Thyroid Function Effects of Mixed Exposure to Urinary Trihalomethanes and Haloacetic Acids. | Environ Sci Technol | 2026 |
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