Asthma is a common chronic inflammatory disease of the airways characterized by variable and recurrent symptoms, reversible airflow obstruction, and spasms. Its common symptoms include wheezing, coughing and shortness of breath, which is known as the triad of asthma. In 2011, 300-235 million people worldwide had asthma, and about 250,000 people die from the disease each year. Symptoms are usually worse at night and in the early morning, or during exercise or in cold weather. Some people with asthma rarely experience symptoms, usually in response to triggers, while others may have persistent and obvious symptoms.
