While somewhere around 10 percent of the population is allergic to animals, among asthma sufferers, 20 to 30 percent of people are allergic to pets. An allergy is the immune system's misguided reaction to certain substances. Although an allergen is essentially harmless, people with pet allergies end up suffering all kinds of cold-like symptoms. Their bodies react to allergens by created immunoglobulin E, which then tells mast cells and basophils to send out chemicals to attack the undesired substances. When an allergy is compounded with asthma, the results can be dangerous.

Most people with dog allergies react to the animal's saliva or dander, which is the flakes of skin the dog sheds. Some people are also sensitive to dog urine and a few are sensitive to hair. Most doctors recommend that people with pet allergies -- and especially those with asthma and allergies -- avoid contact with the allergens as much as possible. Pets without fur, like fish or reptiles, are more likely to be allergen-free. Short-haired animals can be just as allergenic as long-haired ones, since the problem is normally saliva or dander and not the actual fur. Even "hypoallergenic" dogs aren't truly allergen-free.

If allergic and asthmatic people feel they absolutely must have a pet dog, they need to take precautions to limit the allergens they're exposed to. The dog should be restricted to a certain area of the house -- not the bedroom. Anything that can collect allergens, like drapes, carpets or upholstery, should be taken out of the house. A good HEPA air filter is recommended, too. Allergy shots are another possibility, but they're probably not as effective as an asthmatic person would like. Despite environmental and medicinal fixes for dog allergies, it's still safest for someone with asthma and allergies to skip the pet dog.