What You Don't See is What You Get

perennial allergens and steps to avoid them

I just saw a 6 year old child who had problems with a stuffy nose for 3 years. Mom notes his symptoms are worse in the spring through the fall but definitely occur all year round. Mom said that he has problems around other people’s dogs, but not their dog. Allergy testing confirmed significant allergy reactivity to dog dander, cat dander, and dust mites. This is a common problem and leads to difficult decisions on the part of patients and families about treating their disease. Perennial rhinitis is the term we use to describe this child’s problem.

Although our young patient didn’t, some people will report additional symptoms besides nasal stuffiness, including post nasal drainage, facial pressure and/or pain, headache, at times reduced sense of smell. It turns out there are many and varied possible reasons for these symptoms, including allergies, various forms of non-allergic rhinitis, structural nasal problems including large adenoids, and depending on the patient’s age and status, atrophy of the mucous glands, pregnancy, and various occupational triggers.

Allergic rhinitis is best treated using three modalities: avoidance of offending allergens, medication, and if not sufficiently controlled, possible addition of allergy shots or immunotherapy. Avoidance is actually a very effective treatment in many circumstances, and calls for careful environmental attention to allergens in the home to which the person is sensitized. Examples and measures to help avoidance include the following:


Indoor pets are a common source of allergens – typically cats and dogs, although there is an increasing array of more exotic pets including birds, insects, rodents, etc. The most effective measure to control pet allergen exposure is to remove them from the home. The source of the allergen is not the hair or fur, which is easily seen, but in the dander, and in some cases, saliva and urine. Since the dander is easily carried on clothing, banning the pet to one room in the home is often ineffective. In fact, studies indicate that children who sit next to classmates at school with pets in their homes often bring surprisingly high concentrations of animal dander to their own home, at times reaching levels as high as if there actually was an animal in their own home. Non-allergenic or “hypo-allergenic” pet species have been promoted, but to date there is little published scientific evidence that such is the case. No studies have been published to show that in homes with a so-called “hypoallergenic” cat, the levels of free floating cat allergens are lower than homes with other breeds. Other studies examined the concentrations of Can f1 (the principle dog allergen) in homes with “hypoallergenic” and regular dogs and found no difference in allergen levels in the homes of the two groups. Interestingly, there were a few individual animals (not breeds) that seemed to shed less allergen than others within that same breed. Most families find it difficult to remove their beloved pet from the home, and a number of studies have been done to assess other avoidance measures. In general, the only method other than removal is frequent, probably daily, bathing of the animal, which is not feasible. Even when animals are removed from the home, allergens in dander may persist for months. In homes without a pet, highly effective room cleaners and aggressive cleaning may be helpful.


Mice and rats are also potentially very allergenic, at times producing serious and even life-threatening reactions in laboratory workers. Mouse allergens are measurable in almost all inner-city homes and up to 50% of suburban homes, the higher concentrations being in the former. A recent study examining mouse allergy in asthmatics in Baltimore found 51% had significant floor dust concentrations of mouse allergens and positive skin tests. In this asthmatic population, 64% had positive skin tests to cat, 60% for cockroach, 56% for dust mite, and 51% for mouse, but poor asthma outcomes correlated most closely to mouse allergy and less to other allergens tested. Such children were shown to have poor asthma health across a range of outcomes, including increased acute care visits for asthma, reduced lung function, markers of airway inflammation. Effective control measures for mouse allergens requires professional extermination and pest management, along with keeping food and trash in covered containers, cleaning floor and counter tops from food scraps, and sealing cracks in walls, doors and floors.


Evidence that cockroaches are allergenic and may cause perennial allergy symptoms comes from large surveys demonstrating correlation between skin test positivity and symptoms. Homes with higher cockroach allergen concentrations and skin test reactivity have higher rates of hospitalization for asthma. Factors such as humidity, altitude, and food access play an important role in the prevalence and important of cockroaches in allergy. Specific control measures such as placing multiple baited traps or poisons, eliminating potential food sources (garbage, unwashed dishes) are somewhat helpful, but air filters are not helpful because the allergen doesn’t remain airborne very long. Professional extermination may be required for larger infestations. Initial studies were not too encouraging about the usefulness of these eliminations measures in improving symptoms, but more recent trials seeking to reduce exposure simultaneously to cockroach, mite, mice and other indoor allergens together was useful in improving lung function in inner-city children with asthma

Dust mites

Dust mites are microscopic insects in the same class as spiders that live in bedding, sofas, carpets or any woven material. They do not bite, but cause human allergy as a result of mite-specific proteins, toxins, and enzymes excreted in their feces that become airborne and inhaled. Mites absorb moisture from the atmosphere (they do not drink) and feed on organic matter such as shed human and animal skin particles. Infestations are far less common in desert and high-altitude climates, such as Utah and other mountain states, although we do see significant sensitization in some patients who have resided here lifelong. Specific avoidance measures include physical barriers, controlling humidity, reducing reservoirs than can harbor dust mite colonies, heat treatment, chemicals that kill mites, and chemicals that denature or change the mite allergens

  1. Physical barriers include covers for pillows, mattresses, box springs, comforters and furniture cushions. Several products are on the market. The best tolerated mattress and pillow encasements are fabrics that are so tightly woven they allow only very small particles smaller than mite and mite fecal matter to pass through. While use of such encasements as an isolated intervention is probably not sufficient to produce significant clinical improvement, it is an essential component with other measures to reduce mite exposure.
  2. Humidity reduction. It is recommended to reduce relative humidity below 50% to reduce mite growth. Avoid humidifier use or swamp coolers in arid environments such as Utah. Upper floors have less humidity than lower floors and especially basements, particularly if carpets are laid directly on concrete.
  3. Reservoirs. By reducing the presence of carpets, upholstered furniture and drapes, especially in the bedroom, we can reduce the concentration of mites in the home. Use of highly efficient vacuums with special filters (High Efficiency Particulate Air filters or HEPA) can significantly reduce airborne mite allergens. Carpeting removal and replacement with finished floors and washable area rugs, and reduction of stuffed toys in bedrooms are also helpful
  4. Heat Treatment. Steam cleaning of carpets in one study demonstrated killing of dust mites and reduction in mite allergens and improvement in bronchial reactivity. Dry heat treatments of pillows and duvets in dryers have also proven useful. Washing sheets, pillowcases, mattress pads and blankets weekly followed by drying in a clothes dryer on a hot setting effectively reduces mite counts.
  5. Insecticides and allergen-denaturing agents. Use of chemicals to kill mites or denature mite allergens has also been promoted, but has only minor effect.

Careful identification of specific allergies to perennial allergens in patients with perennial rhinitis and asthma, and then implementing specific, proven effective environmental controls can have a significant impact on controlling symptoms. Similarly, ignoring such allergens or attempting to partially treat or remove such allergens will compromise allergy treatment and lead to continued symptoms.