If you can see or smell a fire, chances are the air is unhealthy.
Mike Villegas of the Ventura County Air Pollution Control District said the fine particles impact your health the most.
Villegas said wind after a fire can kick up the fine ash that can get into a person's lungs.
Health experts said people should stay indoors and avoid outdoor activities when a fire is burning nearby.
Villegas said masks used to cover you mouth and nose will keep the large ashes away but it can't keep out the pollution from the haze created by a fire.
Young people with developing lungs and older people with asthma, lung or heart conditions are the most at risk.