Allergies in dogs (Symptoms & causes)

Anaphylaxis is the sudden reaction of the body when it’s exposed to a foreign substance to which it has developed antibodies. It’s a hypersensitivity reaction, which means that the response is an overreaction of the immune system to the allergen.

An anaphylactic reaction can be localized to one are of the body, such as the skin, or it can be widespread and systemic, in which case it’s referred to as anaphylactic shock.

What Causes an Anaphylactic Reaction in a Dog?

At some point before the anaphylaxis, the dog must have been exposed to the allergen already. When that happened, the body responded by producing IgE, which is antibody to the allergen. The IgE binds to mast cells, which are part of the immune system. This first exposure to the allergen causes a small, local reaction, such as an itchy, sore red bump at the site of a bee sting.

This sensitization and the subsequent anaphylactic reactions are an abnormal over-reaction of the immune system.

The next time the dog is exposed to that same allergen, the mast cells recognize it and release their contents in response (histamine is one content of mast cells) and that’s called degranulation and activation of the mast cells. It can cause extreme swelling and redness (an allergic reaction) around a large area.

Sometimes, the initial mast cell response can trigger a chain reaction of mast cells throughout the dog’s body, and that leads to the dangerous condition of anaphylactic shock.

Any substance that is foreign to the body can create an anaphylactic reaction. The most common substances to do so include:

  • Food proteins
  • Insect bites (spiders and bees most commonly)
  • Vaccines
  • Chemicals
  • Medications


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