Learn how to recognize the signs of an allergic reaction in your dog and what you can do at home to help him.

By Deb M. Eldredge, DVM
August 24, 2020
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Just like people, dogs can suffer from allergic reactions. The most common causes of these reactions are insect bites. Fleas rate their own discussion, but bee, wasp, mosquito, and spider bites can all cause your dog some discomfort. Learn to recognize the signs of an allergic reaction in your dog so you can ease his pain and prevent any serious issues.

Swollen Face

One of the most common dog allergic reactions is a swollen face. Picture this: Your dog is playing in the yard. He yelps, and within a minute’s time his muzzle is swollen. The most likely cause is a wasp or bee sting if the swelling happens just after playing outside. Spider bite reactions look similar but tend to take place inside. Luckily most dogs stung or bitten by an insect don’t get the severe allergic reaction some people get, but if your dog is having any problems breathing, rush him to the clinic. That could indicate a full blown anaphylactic reaction.

If your dog’s swollen face doesn’t seem to be related to a bite or sting, it could also be a mild reaction to a vaccine. If that’s the case, the swollen face will occur within a couple hours of receiving a vaccination. Let your veterinarian know if this occurs so he can pretreat before your dog’s boosters or totally alter the vaccination schedule.

Regardless of the reason your dog’s face is swollen, your dog may paw or rub at it. Try to stop that. The itching will just make things worse. A cold compress can bring some immediate comfort. 

You can also give diphenhydramine (Benadryl) to minimize the swelling. The standard dose for dogs is 1 to 2 mg/lb. This can be repeated in 8 to 12 hours. In some cases you may need to give medication for a couple of days. Diphenhydramine should not be given to dogs with glaucoma or heart conditions.

Hives 

Another common dog allergic reaction is bumps or hives on the skin. This is usually from mosquito or other insect bites, but it can also be a general allergic reaction to a plant or other substance that has irritated your dog’s skin. Rarely this could be a reaction to a novel protein (aka something the dog hasn’t eaten before), such as an unusual treat. Hives tend to appear very quickly and disappear faster than a swollen face or muzzle. A cold soaking and some diphenhydramine can help here as well.

Some of these allergic reactions will not fully respond to diphenhydramine alone. In those cases, your dog may need some corticosteroid such as prednisone. This is a prescription medication you will need to get from your veterinarian so if the swelling doesn’t seem to be going down after a few days, check in with your vet.

Itchy Welts

If your dog has raised, very itchy, red welts around the back near the tail, chances are it’s the start of a flea allergy. This can spread to whole body redness and itching. A dog that’s allergic to fleas will react to even one flea bite! Treatment here almost always requires prednisone and, of course, you will need to treat for fleas. That means treating all your pets (even the non allergic ones) plus the environment. Give your vet a call to get treatment started.

Anaphylaxis

The most severe allergic reaction in dogs is anaphylaxis. In this case, while your dog may have a swollen muzzle or hives, she is also struggling to breathe. This is an emergency situation and you should head directly to the nearest vet clinic. If your dog is prone to anaphylaxis (say he has a known severe bee sting allergy) you can ask your vet for a custom dose of an epi pen to keep at home to treat your dog right away.