Asthma triggers can set off asthma symptoms and may differ in patients. Exercise can be a trigger. Other com­mon triggers include allergens like dust and dust mites, furry animals, mold, pollen from trees, grass or flowers, and cockroaches. Irritants that can trigger asthma include aerosols such as hair or bug spray, air pollution, cigarette smoke, and strong odors from per­fumes, air fresheners or cleaning fluids. Asthma can also be brought on by cold air, getting a cold or the flu, and even stress.