What Is An Allergy?
Allergies are hypersensitivity reactions by the body to foreign substances or organisms. Anything that provokes an allergic reaction is called an allergen. Allergens can come from just about anything, and signs can include scratching, stomach upsets, sneezes, rashes and other unusual behavior.

Your veterinarian can tell the difference between an allergy and normal canine behavior. If it is an allergy, your veterinarian will need to identify the allergen and then control the signs of your dog's allergies as best he can. Common categories of allergens include:

• Inhalant allergies: Allergens that are breathed in, including airborne pollen, dust and mold.
• Contact allergies: These affect a dog’s skin upon contact. Among the most common are soaps, insecticides, wool, nylon carpets or grass.
• Flea allergies: An extremely common cause of scratching. The actual allergen is the saliva of the flea, which irritates the skin when the flea bites. Read about Fleas and Ticks.
• Food allergies: Although not common, some dogs react to ingredients in their food. See below for more on food allergies.
• Uncommon allergies, like hormonal hypersensitivity, in which a pet is allergic to her own hormones.
  

Treatment
The goal of managing allergies is to control signs and make your pet comfortable. In most cases, this is done by avoiding the allergen.

If the allergen can't be avoided, medications or injections may be in order. Only your veterinarian can tell you the proper course.

Food Allergies
Some pets develop allergies to food, although this is rare, occurring in less than 1 percent of dogs. Food allergies usually appear as skin problems or as gastrointestinal upsets. A variety of health conditions have similar signs; therefore, other causes should be excluded by your veterinarian before the diet is changed.

Identifying the cause of an allergy requires a detailed medical and diet history, a complete physical examination, and eliminating any other potential causes before trying a new diet.

If a dietary ingredient is suspected to be causing a food allergy, dietary restriction according to a veterinarian's instruction is the only way to isolate that ingredient and determine if it's causing a problem. Restricted ingredient diets (or limited ingredient diets) should be fed for at least 2 to 3 months, and once an animal is placed on a special diet, it is important that no rawhide chews, snacks, treats, table scraps, or other pet foods be offered.

If the ingredient to which the animal is allergic can be identified, a more appropriate diet can be recommended. New diets made with “hypoallergenic” protein sources have been developed. Your veterinarian may recommend one of these special diets if a food allergy is diagnosed in your dog.