Can humidifier disinfectants increase your risk of lung cancer?

What's actually in it

Some people add disinfectant chemicals to home humidifiers to prevent mold and bacterial growth in the water tank. These chemicals include polyhexamethylene guanidine (PHMG) and chloromethylisothiazolinone (CMIT). When the humidifier runs, it aerosolizes these chemicals into a fine mist that you breathe in all night.

The chemicals were never designed to be inhaled. They were meant for surface cleaning. But when atomized by a humidifier, they bypass your body's defenses and land directly on delicate lung tissue.

What the research says

A 2026 study in Cancer Epidemiol used propensity score matching to compare lung cancer rates in people who used humidifier disinfectants versus those who didn't. Users had a higher risk of developing lung cancer even after accounting for smoking, age, and other risk factors.

The damage appears to come from chronic low-level chemical inhalation over months or years of nightly use. The disinfectant chemicals cause repeated inflammation and tissue damage in the lungs, creating conditions that favor tumor development.

Plain distilled water in your humidifier is all you need. Clean the tank regularly with vinegar instead of chemical disinfectants. If you see mold or slime, scrub it out manually rather than adding chemicals that get aerosolized into your bedroom.