Today on World Asthma Day, the National Institutes of Health reaffirms its commitment to biomedical research aimed at preventing the onset of asthma, understanding its underlying causes, and improving the treatment of it. This chronic airway disease, which is characterized by periodic worsening of inflammation that can make it hard to breathe, affects more than 25 million people in the United States, including more than 5 million children. Left untreated, it can be life-threatening.