• Outdoor allergens, such as pollens from grass, trees and weeds
  • Indoor allergens, such as pet dander, dust mites and mold
  • Certain drugs and food additives
  • Irritants in the air, such as smoke, chemical fumes and strong odors
  • Colds, the flu or other illnesses
  • Exercise (although people with asthma can benefit from some exercise)
  • Stress
  • Weather conditions, such as cold air or extremely dry, wet or windy weather