Pets itch from food , environmental allergies, contact allergies, parasites or a combination of the four. Contact allergies include such things as a wool carpet, a nylon collar, a plastic food bowl, or a floor cleaner such as Mop and Glo. The treatment is obviously to remove the offending agent. Food allergies are more insidious and more difficult and frustrating to prove. The only real way to rule out a food allergy is to feed a specially prepared meal that your veterinarian can help with. There are good prescription food trial diets. Just switching from food to food from the pet store usually doesn't get you anywhere, but it is worth a try. Environmental allergies is the main source of itching in pets. Offending allergens include housedust, housedust mites, molds, and tree and weed pollen spores. We used to think that pets inhaled these allergens like people do but it has recently been shown that in pets the allergens actually penetrate the skin wherever they land on the pet (The Inside-Outside Theory). That explains why the feet and ventral abdomen are usually affected more.
The gold standard for diagnosing environmental allergies is by skin testing done by a vet dermatologist. I have several that I can recommend. Alternatively, a less costly blood test can be performed to ID the offending allergen and this test is almost as good as the scratch test. Once it is determined what the pet is allergic to a vaccine can be made for that pet and administered by weekly injections at home or orally on a daily basis. The goal of the vaccine is to cure the pet but in reality if we an reduce the itch by 75% we are all happy.
Besides allergy testing and immunotherapy there are palliative treatments. These include (1) Frequent bathing with or without shampoo (to physically remove the allergens in the hair coat) (2) Room air filters (3) Omega-3 fatty acid supplementation (4) antihistamines like Benadryl (not too helpful in pets) (5) Prednisone - the Silver Bullet, cheap and effective and safe (6) Other immunosuppressants like Atopica and Apoquel (read about these online) (7) Spot-on products that tighten the intercellular spaces on the skin surface making it more difficult for the spores to enter the skin (8) CytoPoint injection - a new injection that turns off the "itch switch" for 4 to 8 weeks. This doesn't tell us why the pet is itching but it sure is nice to see the itch cease for awhile! Recently we have been using Redonyl (PEA) as an adjunct chewable that helps stabilize mast cells which is turn reduces itch.