Mahendra P. Dadhania, MD     Shailen R. Shah, MD     Adele M. Guernica, DO

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Occupational Asthma

Tips to Remember:

Occupational asthma is generally defined as a lung disorder caused by 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 childhood asthma that had previously cleared may recur due to this exposure. In another form of work-related asthma, pre-existing asthma may be aggravated by exposures within the work place.

Symptoms of asthma include wheezing, shortness of breath, chest tightness, difficulty exercising 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 last for a lengthy period in some workers, even if they are no longer exposed to the agents that caused their symptoms. Commonly, symptoms worsen through the work week, improve on the weekend and recur when the worker returns to the job. Less frequently, an accident at work involving a high exposure to irritating fumes or dusts may cause asthma.

In many cases, a previous personal or family history of allergies will make a person more likely to develop occupational asthma. However, many individuals who have no such history still will develop this disease if exposed to conditions that trigger it. Workers who smoke are at greater risk for developing asthma following some occupational exposures. The length of occupational exposure that triggers asthma varies, and can range from months to years before symptoms occur. An accidental irritant exposure can cause asthma within 24 hours.

Many workers with persistent asthma symptoms caused by substances in the workplace are incorrectly diagnosed as having bronchitis. If occupational asthma is not correctly diagnosed early, and the worker protected or removed from the exposure, permanent lung changes may occur and asthma symptoms may persist even without exposure.

Prevalence
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 United States 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. About 5% of people working with laboratory animals or with powdered natural rubber latex gloves have developed occupational asthma. 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 up to 10% of exposed workers.

Causes
Occupational asthma may be caused by one of three mechanisms. These include:

  • Direct irritant effects-Irritants 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)-Allergies 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-Inhalation 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.

Prevention
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/immunologist for an evaluation. In some cases, pre-treatment with specific medications to counteract the effects of workplace substances may be helpful. In other situations, complete avoidance may be necessary.

Common substances that cause occupational asthma
Substance Workers at risk
Acrylate Adhesive handlers
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
Dyes Textile workers
Enzymes Detergent workers, pharmaceutical workers, bakers
Fluxes Electronic workers
Formaldehyde, glutaraldehyde Hospital staff
Gums Carpet makers, pharmaceutical workers
Isocyanates Spray painters, insulation installers, plastics, foam and rubber industry workers
Latex Health care professionals
Metals Solderers, refiners
Persulfate Hairdressers
Seafood Seafood processing workers
Wood dust Forest workers, carpenters, cabinetmakers

Your allergist/immunologist can provide you with more information on occupational asthma.

Tips to Remember are created by the Public Education Committee of the American Academy of Allergy, Asthma and Immunology. This brochure was updated in 2003.

The content of this brochure is for informational purposes only. It is not intended to replace evaluation by a physician. If you have questions or medical concerns, please contact your allergist/immunologist.

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