Indoor Allergen Control Measures: A Practical Summary

By Peter B. Boggs, MD

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The Five Common Indoor Allergens:
Effective Remediation Measures

Cat and Dog Allergen

Cats and dogs are our most common animal cohabitants, present in more than one third of US homes. The cat currently enjoys the status of the most popular pet.

Cat and dog allergens are potent sensitizers. The major cat allergen is Fel d 1, which elicits IgE responses in > 90% of people with cat allergy. Cat albumin is also problematic, accounting for 20% of IgE responses in people with cat allergy. The major dog allergens are Can f 1 and Can f 2, accounting for 75 and 72.5%, respectively, of IgE responses in patients with dog allergy. About 25% of patients also have IgE responses to dog albumin. Fel d 1 and Can f 1 are small-molecular-weight proteins found primarily in animal secretions from sebaceous glands, sublingual salivary glands, perianal glands, and epithelial cells. Structurally, they belong to a family called lipocalins whose purpose is to sense and transport pheromones.²⁶

Aerodynamically, they are carried on particles ranging from 1 to 20 µm in diameter (15% are carried on particles < 5 mm) and can remain airborne for hours to days. This is in marked contrast to the house dust mite, cockroach, and mold allergens, which are carried on large, relatively heavy particles and thus are aerodynamically disadvantaged. The small, light cat and dog allergens are able to circulate on the air currents throughout homes, making it virtually impossible for any room to be "safe."^27,28

Cat allergen particles are also sticky, which leads to widespread distribution in the environment—walls, other surfaces, clothing—and in other places such as homes, workplaces, and schools in which pets have never lived.²⁹

The highly potent nature of pet allergens and their aerodynamic characteristics make remediation options short of total removal of the pet ineffective. Less aggressive measures have not been shown to significantly reduce allergen in settled dust or in the air. Simply said, no other clinical advice is appropriate.

Pet removal should be followed by repeated and extensive cleaning efforts to remove allergen that has fixed to surfaces. Encasement of pillows, mattresses, and springs with materials known to be impermeable to cat allergen is recommended (Table 3). High-efficiency particulate air (HEPA) room filters may also be helpful in removing airborne circulating pet allergen, but their impact on symptoms remains to be established.^30,31

So what does one offer the many pet lovers who are not willing to give up their pets? Compromise measures can be suggested, but should be placed in proper clinical context. Those likely to be somewhat helpful include use of room HEPA filters; isolation of pet to one to two rooms (not a bedroom); frequent (more than once/wk) washing of pet; washing clothing after it has come in contact with the pet; and never allowing a pet in the bedroom. Castration reduces Fel d 1 production but its effect on reducing symptoms is unclear.²⁶ Clinically, pet owners who do not remove pets from the home should have more persistent and severe symptoms with continuous exposure.

The threshold levels for cat (Fel d 1) allergen associated with a maximal risk of sensitization is between 1.7 and 23 mg/g of settled dust. The threshold level to trigger an exacerbation of asthma is unclear. Neither level has been defined for dog allergen.²⁵

Caveats. Even with repeated and extensive cleaning and remediation efforts, it can take up to 6 months after a pet has been removed to begin to see the impact of allergen reduction. Sadly, at this time, there is simply no way to rid an environment of cat or dog allergen short of removal of the pet followed by extensive and repeated cleaning efforts.

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