Many of you understand allergies all too well — because you have them. And maybe some others are even under the care of a physician because of allergies. But others may not understand the scientific basis for allergies. Here, I’d like to try to explain allergy and, in particular, cockroach allergy. To begin, we need to get a few definitions in order.

The word "allergy" means an altered or unexpectedly strong response by the human body to the introduction of an antigen. An "antigen" is a substance that can cause the body to produce anti-bodies. When a foreign substance (like an antigen) enters the body through injection, respiration or ingestion, the body makes antibodies to that substance in order to catch it, kill it or neutralize it.

For some people, the body overreacts to certain antigens (called "allergens" if they produce an allergic reaction), releasing a whole variety of chemical substances into the bloodstream and tissues. This is sometimes called "hypersensitivity." So, in reality, an allergic reaction is really just too much of a good thing. It’s like the body going into overdrive to protect itself when the substance it is "protecting against" isn’t really a threat (things like pollen, mold, house dust mites, etc.). Chemical substances released by the body during an allergic reaction — called mediators of the hypersensitivity response — cause swelling, reddening, pain, itch and heat in the affected areas of the body. For example, if you are breathing an allergen, then swelling, itching and excessive mucous secretion occur in the nose and respiratory tract. If you eat an allergen, then the reaction occurs in the gastrointestinal tract (cramps, diarrhea, etc.). Sometimes, an allergic reaction can be systemic — that is, occurring all throughout the body — resulting in extremely low blood pressure, circulatory collapse and even death.

Only about 20 percent of the human population has allergies. And of those people, not everyone is allergic to the same thing. Some people are allergic to cat dander, some to various pollens, some to certain foods, etc. Someone allergic to bee stings may not be allergic to house dust mites and vice versa. Of course, there are a few people who are hypersensitive to a wide variety of substances.

Hypersensitivity (allergic) reactions are generally divided into four types: I, II, III and IV. These types are based upon which parts of the immune system are activated and the response of various body tissues. Type I is immediate hypersensitivity with symptoms appearing within minutes after the allergen enters the body. Type IV is a delayed reaction, such as reactions to poison ivy. It takes several days for the reaction to occur. Types II and III are more difficult to explain and include things like tissue graft rejection and serum sickness.

Type I reactions cause problems such as inflammation of the nasal membranes and eyes, asthma, eczema, hives, swelling of the skin or mucosal membranes and intestinal disorders. As mentioned, severe reactions can lead to anaphylactic shock and even death.

Cockroach Allergies. In recent years, there has been increasing interest in the role of cockroaches in allergy. As cockroaches die in a dwelling, their decomposing body parts become part of the environmental dust. In areas heavily infested with cockroaches, constant breathing of this dust contaminated with cockroach allergens is unavoidable. Accordingly, many people become sensitized and develop cockroach allergy.

In a study in Thailand, 53 percent of 458 allergic patients had positive skin test reactions to cockroach body parts. In a study in New York City the figure was even higher — more than 70 percent of almost 600 allergic patients visiting seven hospitals reacted positively to cockroach antigen. These numbers reveal that cockroach allergy is fairly common. It has also been hypothesized that cockroach-infested housing is partly to blame for the high incidence of asthma among inner-city children (see related story, pg. 58). In one study of 476 asthmatic children, about 50 percent of the children’s bedrooms had high levels of cockroach allergen in dust. The study also showed that these children had a higher rate of hospitalization than other children.

Prevention, Control AND Treatment. Cockroach inhalant allergy is treated by doctors using symptomatic therapy, immunotherapy with cockroach extracts and intense sanitation and pest control measures to reduce roach populations. Symptomatic therapy includes things like antihistamines, inhaled steroids and decongestants. Immunotherapy — previously called desensitization — involves getting weekly "allergy shots" to lower one’s sensitivity to the particular allergen.

Sanitation efforts should include efficient and frequent house cleaning. For vacuuming, double-thickness filters or HEPA filters are needed for maximum results. Interestingly, even good pest control that kills cockroaches may not eliminate cockroach antigen (allergen) from the dwelling. The shelf life of cockroach allergen is several years. It would be much better to live in a dwelling that has never had a cockroach infestation in the first place.