Asthma is a common chronic inflammatory disease of the airways characterized by shortness of breath, wheezing, coughing and chest tightness . Symptoms are often worse at night or in the early morning, or in response to exercise or cold air. It is caused by a combination of genetic and environmental factors. The prevalence of asthma has increased significantly since the 1970s. As of 2010, 300 million people were affected worldwide. In 2009 asthma caused 250,000 deaths all over the world.