Asthma is a chronic condition involving the respiratory system in which the airway occasionally constricts, becomes inflamed, and is lined with extravagant asthma amounts of mucus, often in response to single or besides triggers. These episodes may be triggered by such things as exposure to an environmental stimulant (or allergen) such as cold weather, warm air, humid air, exercise or exertion, or emotional stress. In children, the most common triggers are viral illnesses similar as those that cause the common cold. This airway narrowing causes symptoms such as wheezing, shortness of breath, trunk tightness, and coughing. The airway constriction responds to bronchodilators. Between episodes, most patients feel well only can have mild symptoms and they may be left behind short of breath after exercise for longer periods of time than the unaffected individual. The symptoms of asthma, which can range from mild to life imminent, can usually be controlled with a combination of drugs and environmental changes. Public attention in the developed world has recently focused on asthma on this account that of its fast increasing prevalence, affecting up to one in four urban children.