Occupational asthma is generally defined as a respiratory disorder
directly related to inhaling fumes, gases, dust or other potentially harmful substances while “on the job.” With occupational asthma, symptoms of asthma may develop for the first time in a previously healthy worker, or pre-existing asthma may be aggravated by exposures within the work place.
Symptoms of asthma include wheezing, chest tightness and cough. Other associated symptoms may include runny nose, nasal congestion and eye irritation. The cause may be allergic or non-allergic in nature, and the disease may persist for a lengthy period in some workers, even if they are no longer exposed to the irritants that triggered their symptoms. Commonly, symptoms worsen through the work week, improve on the weekend and recur when the worker returns to the job.
In many cases, a previous family history of allergies will make a person more likely to suffer from occupational asthma. However, many individuals who have no such history will still develop this disease if exposed to conditions that trigger it. Workers who smoke are at greater risk for developing asthma following some occupational exposures, due to the weakened condition of their lungs. The length of occupational exposure that triggers asthma varies, and can range from months to years before symptoms occur.
Many workers with persistent asthma symptoms caused by irritants in the workplace are incorrectly diagnosed as having bronchitis. People living in residential areas near these factories may also be exposed to harmful triggers of asthma and may suffer symptoms as well. If occupational asthma is not correctly diagnosed early, the long-term prognosis may be guarded, because those suffering with asthma continue to be exposed to the chemicals triggering their condition.
Occupational asthma has become the most prevalent work-related lung disease in developed countries. However, the exact proportion of newly diagnosed cases of asthma in adults due to occupational exposure is unknown. Up to 15% of asthma cases in the U.S. may have job-related factors.
The incidence of occupational asthma varies within individual industries. For example, in the detergent industry, inhalation of a particular enzyme used to produce washing powders has led to the development of respiratory symptoms in approximately 25% of exposed employees. In the printing profession, up to 50% of employees experience respiratory symptoms after constant exposure to gum acacia, which is used in color printing to separate printed sheets and prevent smearing. Isocyanates are chemicals that are widely used in many industries, including spray painting, insulation installation, and in manufacturing plastics, rubber and foam. These chemicals can cause asthma in 10% of exposed workers.
Occupational asthma may be caused by one of three mechanisms. These include:
- Direct irritant effects ÃƒÂ¢Ã¢â€šÂ¬Ã¢â‚¬ÂIrritants that provoke occupational asthma include hydrochloric acid, sulfur dioxide or ammonia, which is found in the petroleum or chemical industries. Workers exposed to these substances will frequently begin wheezing and experiencing other asthma symptoms immediately after exposure to the irritant substance. This is an irritant reaction rather than an allergic reaction, since it does not involve the immune system. Workers who already have asthma or some other respiratory disorder are particularly affected by this type of exposure.
- Allergy (long-term exposure) ÃƒÂ¢Ã¢â€šÂ¬Ã¢â‚¬ÂAllergies play a role in many cases of occupational asthma. This type of asthma generally develops only after long-term exposure (e.g., months or years) to a work-related substance. This is because the body’s immune system needs time to develop allergic antibodies or other immune responses to a particular substance. For example, workers in the washing powder industry may develop an allergy to the enzymes of the bacteria Bacillus Subtilis, and food processing workers may develop an allergy and occupational asthma symptoms from exposure to castor beans, green coffee beans and papain. Allergic occupational asthma can occur in workers in the plastic, rubber or resin industries following repeated exposure to small chemical molecules in the air. Veterinarians, fishermen and animal handlers in laboratories can develop allergic reactions to animal proteins, and health care workers can develop asthma from breathing in powdered proteins from latex gloves or from mixing powdered medications.
- Pharmacologic mechanisms ÃƒÂ¢Ã¢â€šÂ¬Ã¢â‚¬ÂInhalation of some substances in aerosol form can directly lead to the accumulation of naturally occurring chemicals in the body, such as histamine or acetylcholine within the lung, which in turn lead to asthma. For example, insecticides, used in agricultural work, can cause a buildup of acetylcholine, which causes airway muscles to contract, thereby constricting airways.
See the accompanying table for common occupational substances that may cause asthma to develop or trigger temporary aggravation of asthma that is already present.
Once the cause is identified, exposure levels should be reduced. For instance, a worker could be moved to another job within the plant. Employers might consider pre-screening potential employees with lung function tests and then continue to test for symptoms after certain periods on the job once the worker has been hired to ensure that he or she has not developed asthma. Work areas should be closely monitored so that exposure to asthma-causing substances is kept at the lowest possible levels.
Individuals with occupational asthma should see their allergist for an evaluation. In some cases, pre-treatment with specific medications to counteract the effects of workplace substances may be helpful.
Common substances that cause occupational asthma
Workers at risk
|Amines||Shellac and lacquer handlers|
|Anhydrides||Users of plastics, epoxy resins|
|Animal proteins||Animal handlers, veterinarians|
|Cereal grains||Bakers, millers|
|Chloramine-T||Janitors, cleaning staff|
|Drugs/medicines||Pharmaceutical workers,health care professionals|
|Enzymes||Detergent workers, pharmaceutical workers, bakers|
|Formaldehyde, glutaraldehyde||Hospital staff|
|Gums||Carpet makers, pharmaceutical workers|
|Isocyanates||Spray painters, insulation installers, plastics, foam and rubber industry workers|
|Latex||Health care professionals|
|Seafood||Seafood processing workers|
|Wood dust||Forest workers, carpenters, cabinetmakers|