Allergies and Hypersensitivities - Definitions

Allergy

grass is a common allergy in dogsAn allergy is an unexpected reaction that follows the second or subsequent exposure to a particular substance.  This substance, called an allergen or antigen, may be a food, bacteria or a pollen. Indeed almost any environmental substance can act as an allergen such as moulds, food preservatives, dyes, drugs and vaccines.  Substances can enter the body by being breathed in, swallowed, touched or injected.

Like people, some dogs appear to be particularly sensitive to some of these substances. 

Hypersensitivity

Following the primary exposure to the allergen subsequent exposure to the same substance can result in hypersensitivity. This allergic reaction can be described as  immediate or delayed and either systemic (involving the whole body) or local.

Anaphylaxis (please see separate handout) is an example of an immediate type of hypersensitivity.  It can also be systemic in that the whole dog is involved.

Contact dermatitis, on the other hand, is an example of a local hypersensitivity since it only affects the skin that has been in contact with the allergen, e.g. the face, abdomen, paws etc.  To complicate matters contact dermatitis may be immediate, i.e. itchiness, swelling or a rash developing as soon as the dog had come in contact with the allergen, e.g. grass pollen, or it may be delayed and only occur some time after contact.

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