An allergen is a substance that elicits an allergic response, but not in all people. Allergies are the result of a hypersensitive immune system response to what is “normally” a harmless substance. So, curse pollens and dust mites and pet dander all you want, but it is your own immune system that is to blame for your discomfort. A dust mite mattress cover gives you protection and relief.
Believe it or not, the most abundant source of house dust allergens is dust mite poop. The excretions of dust mites are packaged in what amounts to an envelope called a “peritrophic membrane,” and it is certain proteins in this envelope that are responsible for most dust mite allergies. The average mite defecates about twenty times each day. Fecal pellets, like dust itself, easily become airborne, and when inhaled may cause the runny nose, sneezing, and clogged sinuses associated with rhinitis (upper respiratory system inflammation). Coughing, wheezing, shortness of breath, and a “tight” feeling in the chest can be signs of asthma (lower respiratory system inflammation).
The allergens in dust mite feces probably originate in the digestive tract of the dust mites, since the proteins in the poop have been traced to glands surrounding parts of the digestive system in the mites themselves. Dead and living dust mites, upon becoming airborne, will also elicit allergic reactions in people sensitized to the allergens. Ironically, vacuuming and dusting tend to stir dust into the air, causing worse problems for allergic people. Dust mites and their fecal pellets are, however, relatively “heavy,” and they settle again in as little as twenty minutes after cleaning disturbs them.
Clinical diagnosis of dust mite allergy is most often determined by a skin test in which extracts of a variety of common allergy-producing substances are applied to a patient’s forearm or upper back by individual scratches, pricks, or hypodermal injections, one for each potential allergen. A positive reaction to any of the extracts is usually manifested by a red, itchy bump (a “wheal and flare” reaction in allergist terminology). Such a reaction indicates that the patient’s immune system has generated antibodies to combat those allergens.
A blood test that screens for dust mite allergen antibodies is an alternative to the skin test, used in cases where the patient has an existing skin condition or may be taking medications that would interfere with the skin test procedure.
Circumstantial evidence can also lead a doctor to suspect dust mite allergens. For example, should a patient’s symptoms be largely unaffected by seasonal changes, and the patient is spending most of the time indoors, the suspect list for allergens may shrink to food, and various indoor allergens such as pet dander, dust mites, and cockroaches.