An asthma is a condition marked by labored breathing, constriction of the chest, coughing and gasping usually brought on by allergies.

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Other /More definition:
Asthma is a disease characterized by an increased responsiveness of the airways to various stimuli and manifested by slowing of forced expiration which changes in severity either spontaneously or as a result of therapy. The term asthma may be modified by words or phrases indicating its etiology, factors provoking attacks, or its duration.