Animal allergies are most often caused by three things: dander, saliva and urine. These are considered types of allergens because they can trigger an allergic reaction in sensitive individuals.

Dander is tiny flakes of dead skin that animals continually shed. Proteins that are secreted by oil glands in the animal’s skin are also attached to this dander. Because animals are constantly shedding dander, allergens are deposited around any area in which the animal is present. In contained areas, such as a home, the accumulation of dander is more likely to trigger an allergic reaction in people with animal allergies. However, dander is also deposited within the living environment of other animals (e.g., horses, cows) and pests (e.g., rats, mice).

With most animals, the hair or fur has nothing to do with the allergy response. A short-haired animal can cause as many allergy problems as a long-haired animal. Therefore, there is no such thing as a “hypoallergenic” pet or animal. Hairless breeds of cats, for instance, can still be highly allergenic. However, some types of animals may shed less than others, and people with mild allergies may better tolerate these animals.

Animal saliva is another primary cause of allergy symptoms – especially with animals that groom themselves frequently, such as cats. Allergens dry on the fur after grooming and then these dried substances become airborne. Since the allergens are very light, they can stay in the air a long time. They are also sticky and can adhere to furniture, walls, carpet and other textured surfaces.

Animal urine can also cause allergy symptoms – most commonly in pets with enclosed environments (such as indoor cats, guinea pigs, hamsters). An allergy-causing protein is present in the animal’s urine. As the urine dries, these allergens are released into the air and can trigger an allergic reaction.

Because different animals exude different proteins, there is not one specific protein that causes an allergic reaction. A person could therefore be allergic to mice but not to rats and vice versa.

There are other animal-related substances that may cause an allergic reaction in sensitive people. The most common, by animal, are as follows:

The above list is only a sample of the most common animal allergies. Many other animals (such as gerbils, horses, cattle, sheep, deer, birds, reptiles and fish) have been known to cause allergic reactions. Also, animal allergies may be triggered by products made from animals, such as wool, down jackets and comforters, feather pillows, fur coats and some upholstery.

Bird allergies are similar to other animal allergies. Allergens are released as the birds molt, preen themselves and shake feather debris into the air. Bird allergies are also associated with bird urine and droppings.

People can also be allergic to cockroach debris – material that includes outer coverings, saliva, eggs and droppings from cockroaches. Like dust mites, cockroach debris can be found in house dust and bedding.

In some people, insect bites or stings can provoke serious or life-threatening reactions (anaphylaxis). Symptoms may include extensive swelling, nausea, fatigue and fever, and anaphylaxis may include trouble breathing, hives, rapid pulse or drop in blood pressure.

People with animal allergies can safely keep pets without fur or feathers, such as fish, snakes, turtles, lizards, frogs, spiders and hermit crabs. Although fish are usually well tolerated, it is important to note that aquariums can add to the humidity in a room, resulting in an increase in mold and dust mites. An additional concern is that fish food powders are often made from seafood, a common allergen.