Young woman using an inhaler to treat her asthma. Asthma can be triggered by airborne allergens, allergic reactions to some foods, respiratory infections, physical activity cold air pollutants, stress some preservatives and sulfites and or gastroesophageal reflux disease (GERD). Asthma triggers can vary from person to person. An asthmatic person's bronchial tube muscles tighten and thicken. The air passages become inflamed and filled with mucus. This makes breathing very difficult. The illustration on the bottom shows the lungs and respiratory system.