As researchers for the certifying body for personal protective equipment in the United States, we caution against misinterpretation of Wei Huang’s and Lidia Morawska’s contention that face masks could increase health risks from air pollution (Nature 574, 29–30; 2019).

Although the authors attempt to distinguish between ‘medical masks’ and ‘specialist respirators’, a clearer definition of ‘mask’ would avoid confusion over the capabilities of different protective devices. As they point out, surgical masks are loose-fitting and ineffective against air pollution. However, respirators approved by the National Institute for Occupational Safety and Health (NIOSH) fit tightly to the face and filter at least 95% of airborne particles, including aerosolized nanoparticulates (E. Vo et al. Ann. Occup. Hyg. 59, 1012–1021; 2015).

Even NIOSH-approved respirators that have not been personally fitted provide some protection in non-occupational settings (see go.nature.com/35ztfy). Outdoor workers in California, for example, wore such devices as safeguards against non-oily particulate hazards produced by this year’s wildfires (go.nature.com/35jwdw).

An absence of evidence from clinical trials is no reason not to take precautionary measures.