The Real Truth About Cats and Dogs

Can animal lovers with asthma and allergies learn to co-exist with their pet? Robert A. Wood, M.D., separates fact from fiction.

1. Fact or Fiction? Find a new home for your pet and your pet-related allergy symptoms will soon disappear.

   Dr. Wood: Fact and Fiction--There are no convincing studies demonstrating the direct clinical benefits of removing an animal from the home. No research has focused on whether finding a new home for a pet will eliminate the pet-related asthma or allergy symptoms.

   However, there is compelling clinical experience to support the best currently available advice: Finding a new home for the pet is likely to reduce levels of pet-allergen exposure in the home. Avoidance of allergens is always the most appropriate advice a physician can give.

   Once the cat or dog has been removed from the home, symptoms may not improve for weeks or even months, as allergen levels fall quite slowly. In homes with cats, for example, the allergen load typically takes as long as four to six months to reach that of non-cat homes. Levels may fall much more quickly if the homeowner makes extensive environmental changes, such as removing carpets, upholstered furniture, and other allergen reservoirs. It has been shown that cat allergen may persist in mattresses for years after a cat has been removed from a home, so new bedding or impermeable encasements must also be recommended.

2. Fact or Fiction? Some breeds of cats and dogs are less likely to trigger allergy symptoms in people with pet allergies than others.

   Dr. Wood: Fiction--While it is true that some breeds of cats or dogs are said to produce much more allergen than others, there is absolutely no breed that is hypoallergenic or can promise to be best for people with asthma or pet allergies. It is not possible to predict with any accuracy which animals are likely to be more or less allergenic based on a particular breed, size, hair length, or propensity to shed. There is no perfect furry pet for people with allergies to cats and dogs.

3. Fact or Fiction? People who have asthma and exhibit allergy symptoms when exposed to animals tend to have more severe disease.

   Dr. Wood: Fact--A diagnosis of cat or dog allergy can be made by a skin test or blood (RAST) test. If the test is negative, it is very unlikely that cat or dog exposure will affect the asthma in any way. However, if the test is positive, then it is very likely that animal exposure will lead to a worsening of asthma or allergic rhinitis.

4. Fact or Fiction? Washing the cat or dog frequently will reduce the level of allergens in the home.

   Dr. Wood: Neither Fact nor Fiction--A number of studies have investigated measures that might help reduce the allergen load in a home. One study demonstrated significant reductions in airborne cat allergen with a combination of air filtration, cat washings, vacuum cleaning, and removal of furnishings. It was a small study and the purpose was to measure the ability to reduce the allergen load, not to establish any clinical improvement in symptoms. When cat washing was evaluated separately in that study, dramatic reductions in airborne cat allergen were seen after cat washes.

   Subsequent studies have produced conflicting results demonstrating either no change or only a very transient improvement. The current opinion is that the benefits of cat washing are so transient that it is unlikely to be worth the effort or the trauma to the cat. Preliminary information regarding dogs looks very similar.

5. Fact or Fiction? Using a HEPA (high-efficiency particulate air) filter in the bedroom while the dog sleeps next to (not on) the bed makes it possible for man and beast to co-exist happily.

   Dr. Wood: Fiction--While using a HEPA filter helps to remove allergens flowing through the machine, the best advice is to keep the dog out of the bedroom at all times.

   For pet-allergic families who insist on keeping pets, the following recommendations are the best available until pending studies are concluded:

   • Restrict pets to one area of the home when inside.

   • Keep pets out of the bedroom.

   • Use HEPA or electrostatic air cleaners, especially in the room(s) of the person(s) with pet allergies.

   • Remove carpets, upholstered furniture, heavy drapes (that cannot be washed), with a focus on the bedroom--even though the pet is not allowed in the room.

   • Encase pillows, mattress, and box spring with allergen-proof encasings.

   Although tannic acid (chemical product used to typically reduce dust mite allergens) has been shown to reduce cat allergen levels, the effects are modest and short-lived when a cat is present so this treatment should not be routinely recommended.

6. Fact or Fiction? Immunotherapy (allergy shots) makes it possible for pet lovers to keep their pets.

   Dr. Wood: Neither Fact nor Fiction--Most studies over the last 20 years demonstrate a positive effect, particularly for cat allergen. However, the outcomes of these studies have been based largely on laboratory studies, so what this means for the average allergic pet owner remains a question. Based on available studies, it is most likely that immunotherapy will not allow allergic pet owners to live with a cat or dog more comfortably. More studies are needed to fully define the strategies, both immunologic and environmental, that will be most effective.

   Although most asthma and allergies can be controlled by medication, it makes far more sense to begin treatment with allergy avoidance and then to use the least amount of medication possible to control the disease. This approach can have dramatic short-term effects in asthma control and potentially even more important long-term effects in improving the eventual outcome of the asthma.

   In the meanwhile, it is best for patients with significant animal allergy, especially if they have asthma, to find new homes for their pets.