Can animals get allergies just like people?

An allergy is a condition characterized by the exuberantly rejection by the body of something it sees as foreign using an established immune response to that inciting material (allergen). This exuberant hypersensitivity reaction leads to abnormal signs over and above the effect of the infectious agent or material. Direct effects of the agent may include the disease that results from an infection, for example. Animals and humans both can develop allergies but sometimes the pattern of signs or the type of immune reactivity to a specific allergen varies between species.

There are different classes of hypersensitivity reactions based on the components of the immune system that mediate the response. Type I hypersensitivity for example, is classified as an immediate hypersensitivity reaction (e.g., anaphylaxis, atopy). Atopy, or allergic inhalant dermatitis is covered elsewhere on this site. Different immune system mechanisms are involved in delayed hypersensitivity—another class of immune responsiveness. In the delayed reaction, such as occurs in a Type IV hypersensitivity reaction, the signs following exposure to the allergen do not peak for hours to days after exposure. Contact allergy is an example of this latter type of reaction.

All allergens typically result in sensitization of the body's immune system. The body can then recognize the foreign substance, and respond to prevent illness. In the case of allergy, the memory cells produced during initial exposure will lead to an allergy-producing immune cascade after one or more subsequent repeated exposures to the same agent because they significantly over-stimulate the immune response. Often it takes months (or even years) of exposures to trigger a full-blown allergy, so just because an animal currently tolerates something does not mean that an allergy to that same component could not develop at some time in the future.

Some examples of animal allergies:

* Drug Allergies (penicillin, vaccine, etc.)

* Food Allergies (beef, chicken, corn, etc.)

* Parasite Allergies (heartworm microfilariae, flea bite, bee sting anaphylaxis, etc.)

* Contact Allergies (shampoos, insecticides, plastic, flea collars, rubber, cedar chips, etc.)

Allergies may lead to development of signs of illness in a particular body system, though sometimes multiple systems are affected. Examples include:

* Allergic rhinitis (nasal cavity reaction to dust, mold, cigarette smoke, litter dust etc.)

* Allergic pneumonia in dogs (lung reaction from Aspergillus fungus, pollen, heartworm microfilariae etc.)

* Allergic dermatitis (skin reaction due to food allergy, contact allergy, cutaneous drug eruptions, atopy-allergic inhalant dermatitis etc.)

* Allergic gastroenteritis (reaction of stomach and intestines - vomiting, diarrhea due to food allergy)

* Allergic blepharitis (eyelid reaction to molds, dust, pollen, topic medications etc.)

The signs of allergy correlate with the system affected rather than the inciting agent. For example, allergy to beef may show up as skin lesions, diarrhea, vomiting and weight loss in a cat. Corn allergy may produce the same constellation of signs.

For gastrointestinal problems, non-immune reactions to food must also be considered. Food intolerance such as milk intolerance due to loss of the enzyme that functions to break down the milk sugar lactose will lead to signs such as vomiting and diarrhea, but this type of sensitivity is not a true allergic reaction. Likewise, contact allergic dermatitis of the skin should be differentiated from irritant contact dermatitis. The latter case is due to physical or chemical irritation rather than an overactive immune response.