People with animal allergies have allergic reactions after coming into contact with one or more animals to which they are sensitive. Contrary to popular perception, it is not the animal’s fur that causes most allergic reactions. Rather, it is flakes of skin (dander) and dried urine, saliva or blood proteins that most often trigger an allergic reaction. Reactions are also possible with non-fur animals such as birds and insects.

An animal allergy occurs when the body’s immune system overreacts to a normally harmless substance associated with the animal, usually some type of protein from its dander, saliva or urine. These miniscule proteins are carried through the air, where they can land on the lining of the nose or eyes. They can also be inhaled directly into the lungs. Once the protein enters the body, it starts a cascade of events that triggers the immune system and eventually leads to an allergic reaction.

How this reaction manifests itself often depends on the individual. An allergic reaction can affect the skin, gastrointestinal tract, respiratory system or even the heart and blood vessels. Physical symptoms include sneezing, watery eyes and runny nose. They can also include sore throat, coughing, blotchy skin and other symptoms that may be confused with other causes, such as colds and flu. In addition, animal allergies can trigger asthma attacks in susceptible people. Studies have shown that up to 67 percent of children with asthma are sensitive to animal allergens.

Direct contact with an animal is not needed to develop an allergy. Flakes from dander, saliva and urine products are extremely lightweight and easily become attached to larger particles, which can become airborne or stick to surfaces or objects. These particles remain in the environment for weeks or even months after an animal has departed.

In fact, an animal does not have to live within a home for its allergens to be present. Researchers have documented the presence of animal allergens in homes, office buildings and other environments where animals did not live. In some cases, the amount of animal allergen found was quite high. Therefore, people can experience an allergic reaction to an animal without ever having to touch it or even be near the animal.

Animal allergies may not develop quickly, and it is not unusual for animal allergies to take more than two years to develop. Allergies occur when a person’s body begins to produce a specific type of antibody called immunoglobulin E (IgE) to combat the allergen.

This process, known as sensitization, does not usually trigger allergy symptoms at first. However, when a person has become sensitized, the next exposure to the allergen can trigger an allergic reaction. The allergen comes into contact with IgE antibodies, which are attached to specialized white blood cells called mast cells. The mast cells release histamine and other chemicals that cause symptoms such as sneezing, watery eyes and coughing.

It can take weeks or even several years to create a new antibody, which is the reason why people may not be allergic to their puppy until it becomes an adult dog. In addition, puppies and kittens have no old skin to shed and therefore produce less dander. Some people may be able to tolerate baby animals but not adults. Why some people develop allergies and others do not is unknown, and research is ongoing.

One study suggests that exposure to animals during early childhood may decrease the risk of developing allergies. Researchers found that children exposed to cats or dogs during their first year of life were less than 50 percent as likely to develop animal allergies by the time they were 6 or 7 years of age.

Specific allergies are not inherited. However, a person’s risk of developing an allergy (of any type) increases if a parent has an allergy. So, a child whose parent is allergic to dog dander is more likely to develop an allergy of some type, although not necessarily to dog dander.

Some people report that they have outgrown their animal allergies once they reach adulthood. This is believed to be an illusion because once the body becomes sensitized to an animal allergen, it stays that way for life. However, symptoms can taper off in older age. The immune system weakens and the body is not strong enough to react to the same allergies it did during childhood and young adulthood.