- Tobacco smoke
- Infections such as colds, flu, or pneumonia
- Allergens such as food, pollen, mold, dust mites, and pet dander
- Exercise
- Air pollution and toxins
- Weather, especially extreme changes in temperature
- Drugs (such as aspirin, NSAID, and beta-blockers)
- Food additives (such as MSG)
- Emotional stress and anxiety
- Singing, laughing, or crying
- Smoking, perfumes, or sprays
- Acid reflux
