Do essential oil diffusers release harmful chemicals into your indoor air?

What's actually in it

Essential oil diffusers heat or vibrate concentrated plant oils to fill a room with scent. These oils aren't just pleasant aromas. They're complex chemical mixtures containing terpenes, alcohols, aldehydes, and other volatile organic compounds (VOCs). When released into the air, these compounds react with ozone and other indoor pollutants to form secondary pollutants like formaldehyde and ultrafine particles.

Tea tree oil, eucalyptus, and pine-based oils are especially high in terpenes like limonene and alpha-pinene, which are among the most reactive VOCs in indoor settings.

What the research says

A 2025 study in J Occup Environ Hyg measured VOC and particle emissions from essential oil diffusers running with tea tree oil in a controlled setting. The researchers tracked what chemicals were released and at what concentrations, then compared them to health-based exposure limits.

The diffusers released measurable amounts of terpenes, alcohols, and other VOCs into the air. The concentrations increased with longer diffusing times and smaller room sizes. Some compounds reached levels that could irritate airways in people with asthma or chemical sensitivities.

The study also detected fine and ultrafine particles released during diffusing. These tiny particles can penetrate deep into the lungs. The combination of VOCs and particles means diffusers contribute to indoor air pollution, even though they're marketed as natural and healthy.

If you use a diffuser, run it for short periods with good ventilation. Avoid diffusing in bedrooms while sleeping. People with asthma, allergies, or young children in the home should be especially cautious.