這是ASPCA的推薦貼，而非廣告貼。有Prescription的香波呢，看有沒有必要

http://www.aspca.org/pet-care/dog-care/dog-care-allergies.aspx

How Can Dog Allergies Be Treated?

The best way to treat allergies is to remove the offending allergens from the environment.

• Prevention is the best treatment for allergies caused by fleas. Start a flea control program for all of your pets before the season starts. Remember, outdoor pets can carry fleas inside to indoor pets. See your veterinarian for advice about the best flea control products for your dog and the environment.
• If dust is the problem, clean your pet's bedding once a week and vacuum at least twice weekly—this includes rugs, curtains and any other materials that gather dust.
• Weekly bathing may help relieve itching and remove environmental allergens and pollens from your dog’s skin. Discuss with your vet what prescription shampoos are best, as frequent bathing with the wrong product can dry out skin.
• If you suspect your dog has a food allergy, she’ll need to be put on an exclusive prescription or hydrolyzed protein diet. Once the allergy is determined, your vet will recommend specific foods or a home-cooked diet.

Are There Allergy Medications for Dogs?

Since certain substances cannot be removed from the environment, your vet may recommend medications to control the allergic reaction:

• In the case of airborne allergens, your dog may benefit from allergy injections. These will help your pet develop resistance to the offending agent, instead of just masking the itch.
• Antihistamines such as Benadryl can be used, but may only benefit a small percentage of dogs with allergies. Ask your vet first.
• Fatty acid supplements might help relieve your dog’s itchy skin. There are also shampoos that may help prevent skin infection, which occurs commonly in dogs with allergies. Sprays containing oatmeal, aloe and other natural products are also available.
• An immune modulating drug may also be helpful.
• There are several flea-prevention products that can be applied monthly to your dog’s skin.
• If the problem is severe, you may have to resort to cortisone to control the allergy. However these drugs are strong and should be used with caution and only under the guidance of your veterinarian.