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"Allergies, also known as hypersensitivities, are acquired overreactions by a dog&amp;rsquo;s immune system to something that it perceives as being foreign and potentially dangerous, called an &amp;ldquo;allergen.&amp;rdquo; Common canine allergens are food ingredients, pollens, grasses, weeds, plants, flea and tick saliva, mites, chemical cleaners, detergents and other household products, plastics, drugs, carpet fibers and cigarette and cigar smoke. Allergies often cause skin problems, ear irritation and gastrointestinal upset. Affected dogs may scratch, lick or bite at irritated skin areas, creating sores that can become infected. The constant head shaking and scratching from &amp;ldquo;allergic ears&amp;rdquo; can cause blood-filled blisters, called hematomas, on the bottom of the ear flaps. Dogs with allergies can develop significant behavioral changes because of the inescapable discomfort associated with their condition."^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.petwave.com/Dogs/Health/Allergies.aspx>