Do you wheeze, cough or feel short of breath at work, but not during weekends and vacations?

If so, you may have occupational asthma, a lung disease caused by inhaling workplace fumes, gases or dust. In developed countries, it's the most common work-related lung disease. Although its exact prevalence is unknown, some researchers estimate it may account for 9 percent of asthma cases.

Occupational asthma can develop if you never had asthma before or had childhood asthma that previously cleared. It can also worsen any pre-existing asthma.

With treatment, occupational asthma is usually reversible. But the only sure way to prevent its worst consequence — permanent lung damage — is to completely avoid the substance that's causing the disease. If that's not possible at your workplace, your doctor may recommend that you find a new job in a different line of work.

Signs and symptoms of occupational asthma may include:

• Wheezing
• Coughing
• Shortness of breath
• Chest tightness
• Difficulty exercising

Other possible accompanying signs and symptoms may include:

• Runny nose
• Nasal congestion
• Eye irritation

During the early stages of the disease, you usually develop symptoms shortly after exposure to the workplace substance that causes it. Sometimes, you may not notice any signs or symptoms until up to 12 hours later. Your asthma may worsen as your work week progresses, subside during weekends and vacations, and recur when you return to work.

In later stages of the disease, you may also develop signs and symptoms when you're away from work. Once your lungs have developed a pattern of overreacting to a certain substance, you may become sensitive to other substances, such as house dust, cigarette smoke and cold air.

More than 250 workplace substances have been identified as causes of occupational asthma. These substances typically fall into one of six categories:

• Animal substances. These include proteins found in dander, hair, scales, fur, saliva and body wastes.
• Chemicals. These include anhydrides, diisocyanates and acids used to make paints, varnishes, adhesives, laminates and soldering resin. Other examples include chemicals used to make insulation, packaging materials, and foam mattresses and upholstery.
• Enzymes. These are used in detergents, flour conditioners, some pharmaceuticals and meat tenderizers.
• Metals. The most problematic ones include platinum, chromium and nickel sulfate.
• Plant substances. These include proteins found in natural rubber latex, flour, cereals, cotton, flax, hemp, rye, wheat and papain, a digestive enzyme derived from papaya.
• Respiratory irritants. Examples include chlorine gas, sulfur dioxide and smoke.

Occupational asthma may be caused by one of three processes:

• Direct irritation. You may develop symptoms immediately after exposure to substances such as ammonia, sulfur dioxide, chlorine, hydrochloric acid and environmental smoke. This is an irritant reaction rather than an allergic reaction since it is primarily a trigger of pre-existing asthma.
• Allergic sensitization. Your body develops an allergy from continued exposure to a specific substance. Symptoms of occupational asthma emerge when your immune system produces specific antibodies against the substance and triggers the release of inflammatory chemicals such as histamine. The sensitization process may take less than a year or it may take several years.
• Pharmacologic reaction. Some substances increase your body's natural production of chemicals that trigger occupational asthma symptoms, such as histamine and acetylcholine. Insecticides, for example, can cause a buildup of acetylcholine in your lungs.

You're at risk of developing occupational asthma if you work around substances that are known to cause the disease. Although a family or personal history of allergies or asthma may elevate your risk, many workers without such a history also develop occupational asthma.

Smoking, especially on the job, may significantly increase your risk. The heat from burning tobacco can change workplace chemicals into more harmful substances as you inhale them through a cigarette. For example, if you smoke around trichloroethylene — a commonly used industrial solvent — it can convert this chemical into lung-damaging phosgene gas.

It's possible to develop occupational asthma in almost any workplace. But your risk is highest if you work in certain occupations. Here are some of the riskiest jobs and the asthma-producing substances associated with them.

If you have respiratory problems that occur or worsen at work and get better when you're away from work, seek prompt evaluation by a doctor.

Diagnosing occupational asthma is similar to diagnosing nonoccupational asthma. But there's an important difference. Because occupational asthma is covered by state workers' compensation laws, your doctor will evaluate whether or not your job is either causing your asthma or making it worse. This can be difficult and time-consuming.

During an occupational asthma evaluation, your doctor will ask you many questions about your symptoms, your job and how they may be related. So you'll need to provide a detailed description of working conditions at your present and previous jobs.

Tell your doctor about any workplace exposure to fumes, gases, smoke, irritants, chemicals, and plant and animal substances, or environmental conditions such as extreme heat, cold or dryness. Bring a list of specific substances you are exposed to at work, if possible. Also describe any respiratory symptoms you have when you're away from work. This may help your doctor determine if you have occupational asthma, nonoccupational asthma or some other condition such as bronchitis.

On the basis of your medical history and a physical examination, your doctor may suspect that you have occupational asthma. He or she may ask you to perform a lung (pulmonary) function test.

Spirometry — a noninvasive test that measures how well you breathe — is the preferred test for diagnosing occupational and nonoccupational asthma. During this 10- to 15-minute test, you take deep breaths and forcefully exhale into a hose connected to a machine called a spirometer.

If certain key measurements are below normal for a person your age, it may be a sign that your airways are obstructed. Your doctor may ask you to inhale a bronchodilator drug used in asthma treatment to open obstructed air passages. Then you retake the spirometry test. If your measurements improve significantly, it's likely that you have asthma, but it may not be occupational asthma.

To determine if you have occupational asthma, your doctor may ask you to carry a peak flow meter, a small, hand-held device that measures the rate at which you can force air out of your lungs. You'll likely be asked to exhale forcefully into the peak flow meter at selected intervals during working and nonworking hours.

You may be asked to use a special kind of peak flow meter that automatically records results. If your breathing improves significantly when you're away from work, you may have occupational asthma.

To identify the cause of your symptoms, your doctor may arrange for air quality measurements at your workplace. If he or she suspects that you're sensitive to a plant or animal protein, you may be asked to have an allergy skin test. During such tests, your skin is exposed to purified allergy extracts and observed for signs of an allergic reaction.

Allergy skin tests can't be used to diagnose chemical sensitivities, but may be useful to evaluate sensitivity to animal dander, mold, dust mite and latex. So your doctor may recommend that you have certain tests at a specialized testing center. Because there are only a few such centers in the United States, travel may be required.

During one such test — a challenge test — you inhale an aerosol containing a small amount of a suspect chemical and are observed for signs and symptoms of asthma. Other tests may include an analysis of your breath for nitric oxide gas, high levels of which are associated with asthma, and an analysis of your coughed up phlegm for signs of abnormal cells.

The longer you're exposed to a substance that causes occupational asthma, the worse your symptoms will become. Left untreated, occupational asthma can cause permanent lung damage that requires treatment with medications, physical therapy or supplemental oxygen. It can also cause a fatal asthma attack.

The best treatment for occupational asthma is to completely avoid the workplace substance that causes your symptoms.

But that's easier said than done. Once you become sensitive to a substance, even tiny amounts of it can trigger asthma. As long as the substance is used in your workplace, you probably won't be able to completely avoid it, even if you wear a mask or respirator.

If you have occupational asthma, your doctor may prescribe asthma medications to help relieve your symptoms. Asthma medications include:

• Long-term control medications to reduce inflammation. Examples include inhaled corticosteroids such as fluticasone (Flovent) and budesonide (Pulmicort), and long-acting beta-2 agonists such as salmeterol (Serevent) and formoterol (Foradil). Advair Diskus contains both fluticasone and salmeterol.
• Quick-relief medications to open congested airways. Examples include albuterol (Proventil, Ventolin, others).

If you have severe occupational asthma and stay at your job, asthma medications are unlikely to keep your condition from worsening. But such medications may help prevent permanent lung damage or even reverse your asthma if you leave the workplace for a new job in a different line of work.

Your current employer may be able to transfer you to another job at your company where you won't be exposed to the substance that causes your disease. If that's not possible, you may need to look elsewhere for employment.

Changing jobs has many potential downsides. Although you may find an acceptable job close to home, you may have to take a pay cut, relocate to a new city or return to school for additional job training.

Your doctor won't likely recommend that you change your job without careful consideration. Work with your doctor to make the best decision for your overall health.

If you haven't yet entered the work force, you may be able to prevent occupational asthma by avoiding employment in high-risk professions. This may be especially important if you have a family or personal history of allergies or asthma.

If you accept or already have a job in a high-risk profession, your company has legal responsibilities to help protect you from hazardous chemicals. Under guidelines established by the Occupational Safety and Health Administration (OHSA), your employer is required to do the following:

• Inform you if you'll be working with any hazardous chemicals.
• Train you how to safely handle these chemicals.
• Train you how to respond to an emergency, such as a chemical spill.
• Provide protective gear, such as masks and respirators.
• Offer additional training if a new chemical is introduced to your workplace.

Under OSHA guidelines, your employer is required to keep a Material Safety Data Sheet for each hazardous chemical that's used in your workplace. This is a document that must be submitted by the chemical's manufacturer to your employer. You have a legal right to see and copy such documents. If you suspect you're allergic to a certain substance, show the Material Safety Data Sheet to your doctor.

While at work, be alert for unsafe and unhealthful working conditions and report them to your supervisor. If necessary, call OSHA and ask for an on-site inspection. You can do this so that your name won't be revealed to your employer.

If you smoke, quit now. In addition to all its other health benefits, being smoke-free may help prevent occupational asthma.

Although you may rely on medications to relieve symptoms and control inflammation associated with occupational asthma, you can do several things on your own to maintain overall health and lessen the possibility of attacks:

• Avoid irritating gases. Occupational asthma may be worsened by exposure to sulfur dioxide, a pollutant released by coal-burning power plants; nitrogen dioxide, a pollutant released by automobiles and natural gas stoves; and chlorine, a disinfectant used in swimming pools.
• Exercise. Regular exercise can strengthen your heart and lungs so that they don't have to work so hard. Aim for 30 minutes of exercise on most days. If you've been inactive, start slowly and gradually increase your activity over time. Avoid exercising outdoors during pollution alerts or when the temperature is below zero. Discuss any exercise program with your doctor.
• Minimize household allergens. Common household substances, such as mold, pollen, dust mites and pet dander, can aggravate symptoms of occupational asthma. Air conditioners, dehumidifiers and thorough cleaning practices, especially in your bedroom, can minimize your exposure to these substances and help you breathe easier.

Because occupational asthma can affect both your health and career, it's often a double whammy. Coping with asthma is complicated enough without the added stress of searching for a new job. So you may become frustrated, angry or depressed.

If you're feeling overwhelmed, consider seeing a personal or career counselor or joining an asthma support group. Sharing your experiences with others may help you better understand your condition and take control of your treatment, which is the best way to overcome feelings of anxiety and helplessness.