Asthma is a respiratory disorder characterised by breathlesnes, coughing and wheezing. The bronchial pasages, which carry air to the lungs, become constricted. It may be brought on by a variety of stimuli; an allergic reaction to a substance; as a result of respiratory infection; or it may be caused by exertion, certain drugs, or strong emotion. Anti-asthma drugs are divided into preventers, designed to protect the sufferer's airways, making an attack les likely to occur, and relievers, which alleviate the symptoms when an attack does occur. Both are commonly administered via aerosol inhalers. There are an estimated 150 million asthma sufferers worldwide, with the prevalence of the condition increasing.
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