Asthma is a chronic disease marked by periodic attacks of wheezing and difficulty breathing, especially exhaling. During an asthma attack, the air passages in the lungs become narrow or blocked by mucus or a muscle spasm. Asthma attacks can be triggered by allergens such as pollen, animal dander, molds, fungi, chemicals in certain foods, or house dust. Irritants such as tobacco smoke, smog, exhaust fumes, household cleansers, and other chemicals may also cause asthma attacks. Even sudden changes in temperature or humidity, strong winds, and strenuous exercise may trigger attacks. Occasionally, the attacks are precipitated by an upper respiratory tract infection. Allergy testing, either by the skin or the blood, can be helpful in pinpointing the exact cause. Asthma treatment begins by identifying and avoiding the factor that causes the attacks. In most cases, an attack can be controlled by using an inhaler, which produces a fine mist that is inhaled directly into the bronchial tubes. Severe attacks may need to be treated by medication which relaxes the bronchial muscles. Advances in the treatment of asthma include newer drugs with different methods of delivery and immunotherapy, which desensitizes the lungs to the allergen that is responsible for the attacks. For more information about asthma, contact a health care provider.