Allergies, mediators and asthma

Asthma is a term that has been used for centuries to describe states of breathlessness associated with wheezing. However, there are well‐known difficulties in defining asthma, as it encompasses such a broad clinical spectrum ranging from mild, rapidly reversible, broncho‐spasm to severe, intractable, chronic airflow obstruction. Moreover, reversibility of airflow obstruction, a cardinal feature used to identify asthma, may be demonstrated only with difficulty in certain cases, such as severe, acute asthma attacks, which necessitate several days of treatment before any reversibility can be achieved.