When most people think of allergy "triggers," they often focus on plant pollens, dust, animals and stinging insects. In fact, cockroaches also can trigger allergies and asthma.

Cockroach allergy was first reported in 1943, when skin rashes appeared immediately after the insects crawled over patients' skin. Skin tests first confirmed patients had cockroach allergy in 1959.

In the 1970s, studies made it clear that patients with cockroach allergies develop acute asthma attacks. The attacks occur after inhaling cockroach allergens and last for hours. Asthma has steadily increased over the past 30 years. It is the most common chronic disease of childhood. Now we know that the frequent hospital admissions of inner-city children with asthma often is directly related to their contact with cockroach allergens-the substances that cause allergies. From 23 percent to 60 percent of urban residents with asthma are sensitive to the cockroach allergen.

The increase in asthma is not fully understood. Experts think one reason for the increase among children is that they play indoors more than in past years and thus have increased contact with the allergen. This is especially true in the inner cities where they stay inside because of safety concerns.

The job of immune system cells is to find foreign substances such as viruses and bacteria and get rid of them. Normally, this response protects us from dangerous diseases. People with allergies have supersensitive immune systems that react when they inhale, swallow or touch certain harmless substances such as pollen or cockroaches. These substances are the allergens.

Cockroach allergen is believed to derive from feces, saliva and the bodies of these insects. Cockroaches live all over the world, from tropical areas to the coldest spots on earth. Studies show that 78 percent to 98 percent of urban homes have cockroaches. Each home has from 900 to 330,000 of the insects.

Private homes also harbor them, especially if the homes are well insulated. When one roach is seen in the basement or kitchen, it is safe to assume that at least 800 roaches are hidden under the kitchen sink, in closets and the like. They are carried in with groceries, furniture and luggage used on trips. Once they are in the home, they are hard to get rid of.

The amount of roach allergen in house dust or air can be measured. In dwellings where the amount is high, exposure is high and the rate of hospitalization for asthma goes up. Allergen particles are large and settle rapidly on surfaces. They become airborne when the air is stirred by people moving around or by children at play.

People with chronic severe bronchial asthma are most likely to have cockroach allergy. Also likely to have it are people with a chronic stuffy nose, skin rash, constant sinus infection, repeat ear infection and asthma.

Cockroach allergy is a problem among people who live in inner-cities or in the South and are of low socioeconomic status. In one study of inner- city children, 37 percent were allergic to cockroaches, 35 percent to dust mites, and 23 percent to cats. Those who were allergic to cockroaches and were exposed to the insects were hospitalized for asthma 3.3 times more often than other children. This was true even when compared with those who were allergic to dust mites or cats.

Cockroach allergy is more common among poor African Americans. Experts believe that this is not because of racial differences; rather, it is because of the disproportionate number of African Americans living in the inner cities.

Symptoms vary. They may be a mildly itchy skin, scratchy throat or itchy eyes and nose. Or the allergy symptoms can become stronger, including severe, persistent asthma in some people. Asthma symptoms often are a problem all year, not just in some seasons. This can make it hard to determine that a cockroach allergy is the cause of the asthma.

The National Heart, Lung, and Blood Institute recommends that all patients with persistent asthma be tested for allergic response to cockroach as well as to the other chief allergens, dust mites, cats, dogs and mold.

Diagnosis can be made only by skin tests. The doctor scratches or pricks the skin with cockroach extract. Redness, an itchy rash, or swelling at the site suggests you are allergic to the insect.

Cockroaches should be suspected, though, when allergy symptoms-stuffy nose, inflamed eyes or ears, skin rash or bronchial asthma-persist year round.

If you have cockroach allergy, avoid contact with roaches and their droppings.

• The first step is to rid your home of the roaches. Because they resist many control measures, it is best to call in pest control experts.
• For ongoing control, use poison baits, boric acid and traps. Don't use chemical agents. They can irritate allergies and asthma.
• Do not leave food and garbage uncovered.
• To manage nasal and sinus symptoms, use antihistamines, decongestants and antiinflammatory medications. Your doctor will also prescribe antiinflammatory medications and bronchodilators if you have asthma.
• If you keep having serious allergic symptoms, see an allergist about "allergy injections" with the cockroach extract. They can reduce symptoms over time.