No one really knows what causes asthma, but doctors have identified at least 10 known triggers including allergies, food additives, and more. Learn more about asthma triggers at WebMD., Asthma triggers are things that set off or make asthma symptoms worse. Common triggers include: Indoor allergens, such as dust mites, mold, and pet dander or fur; Outdoor allergens, such as pollens and mold; Emotional stress; Physical activity, although with treatment you or your child should still be able to stay active, An asthma trigger is a thing, activity or condition that makes asthma worse. When you encounter a trigger it can cause a sudden worsening of symptoms, often called an asthma attack, episode or flare-up. Common asthma triggers include respiratory infections, allergens, irritants, exercise and emotions. Knowing what causes your asthma symptoms is , Asthma is a common respiratory condition that can make it difficult to breathe. Being exposed to certain triggers can make it more likely for you to have asthma attacks. Common triggers for asthma include environmental factors, exercise, and certain medications., Nonallergic outdoor irritants (see Table 17-3) that trigger asthma are also exceedingly common and important to identify and eliminate.Studies have implicated several outdoor pollutants as potential triggers of asthma symptoms. Air pollutants such as ozone, nitrogen oxides, acidic aerosols, and particulate matter can lead to asthma symptoms and frank exacerbations., Common asthma triggers Colds, flu and other respiratory infections. Colds and flu can hit hard if you have asthma. In fact, the common cold is behind around 4 out of 5 bad asthma attacks. Check out our Asthma Winter Checklist for great tips on how to avoid these types of triggers..