How do Allergy Symptoms Develop?

The hallmark symptoms of common dog allergies include itchiness and inflammation of the skin. These symptoms occur when the dog's allergen-specific IgE antiboides release some chemicals that cause the symptoms. The exact mechanism is rather complex. Here is a simplified explanation:

When a dog is exposed to an allergen (e.g. fleas, pollen), IgE antibodies are formed by the dog's white blood cells. The IgE antibody attaches to a tissue cell called a mast cell. The next time the dog is exposed to the allergen, the allergen attaches to the IgE antibody-mast cell combination. When that happens, the mast cell sort of "explodes" and releases chemicals within the cell and cell membrane. These chemicals include, among others, histamine and various prostaglandins which are responsible for causing the clinical signs of common dog allergies including itching and inflammation.