In the lungs, this warm, moist air normally travels through millions of treelike branches that are covered with a layer of mucus. Mucus is sticky and can trap small particles before they damage the lungs or block an airway. Mucus moves upwards toward the mouth and nose where coughing, sneezing and swallowing removes it along with any trapped particles. During an asthma attack, muscles surrounding the treelike branches tighten, the inner walls of the lungs swell and mucus production increases. This results in constriction and sometimes the complete blockage of airways.
Individuals are more likely to have asthma if there is a family history of the disease.
Several biological and environmental factors can trigger an asthma attack. Allergy plays a key role in about half of all asthma cases. After exposure to an allergen, the body releases chemicals that produce conditions associated with an attack. Common allergens in the environment are pollen, dust mites, cockroaches, bacteria, molds, animal hair and animal dander. Allergens also may originate from food and food additives.