Ozone from ionizers
Many ion generators also produce ozone, a lung irritant that causes coughing, chest tightness and can aggravate asthma. The US EPA notes that some units exceed health standards even when used as directed, and that ozone at safe levels does little to clean indoor air. The California Air Resources Board adds that ozone reacts indoors to form formaldehyde and ultrafine particles.
A room-scale experiment found an ion generator increased ozone, formaldehyde and other compounds, and raised ultrafine particles when a scented air freshener was present.
If you buy an air cleaner
- Look for CARB certification (ozone emissions limited to 0.050 ppm).
- Avoid products that generate ozone deliberately, or that call ozone “activated oxygen” or “fresh air”.
- Don’t run ion generators together with scented products.
- Clean nearby surfaces — ionizers deposit particles on walls and furniture.
Radioactive minerals in “anion” products
Some “negative ion” powders and fabrics use monazite, which contains thorium. Regulators in Korea, Taiwan and the Netherlands have acted against such products — mattresses, pillows, pendants, bracelets and masks — and the US Nuclear Regulatory Commission has published a fact sheet. Regulators’ concern centres on items worn against the skin for long periods. See our clothing guide for what to ask a seller.
Use alongside care
The best evidence for negative ions is as an add-on for seasonal or chronic depression, using powered generators under study conditions. It is not a substitute for medical treatment. Anyone with depression, asthma or a heart or lung condition should talk to a doctor before relying on any device.