When pollution settles over Utah's valleys in the wintertime, sometimes creating the dirtiest air in the country, some residents don breathing masks to protect themselves.
Experts say they aren't necessarily a cure-all. The masks usually aren't tight-fitting enough to protect a person's lungs and they don't have filters fine enough to stop the tiny particulate matter that is harmful.
If they fit both categories, a person would have struggle to breathe while doing physical activities.
That's why the Utah Division of Air Quality doesn't make any recommendations about masks.
Brian Moench, an anesthesiologist and president of Utah Physicians for a Healthy Environment, says people would be better off buying air purifiers for their bedrooms.
Northern Utah has endured heavy pollution this winter from winter inversions caused by weather and geography.