Too much mucus is produced. These changes all make breathing difficult. Occupational asthma is usually reversible, but permanent lung damage can occur if exposure to the substance that causes the disease continues. In highly sensitive persons, even very low levels of exposure may provoke an episode. Sometimes the worker will only have a cough or any one of the other symptoms.
Symptoms usually occur while the worker is exposed to a particular substance at work.
In some cases, symptoms may develop several hours after the person leaves work, and then subside before the worker returns to the job the next day. In the early stages of the disease, symptoms usually decrease or disappear during weekends or vacations, only to recur upon return to work. In later stages of the disease, symptoms may occur away from work after exposure to common lung irritants. Once the airways have a pattern of overreacting, many common substances such as cigarette smoke, house dust, or cold air may produce asthma-like symptoms. Workers in hundreds of occupations are exposed to substances in the air that may cause occupational asthma in susceptible people.