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.