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Ask the Vet: Itchy Pets & Allergies by Stefanie Wong, DVM
February 20, 2016

Why is my pet itching so much?

This time of year we have a lot of dogs (and even some cats!) coming in for itching, chewing, licking, hair loss and skin rashes. In the majority of these cases, the underlying cause is allergies; however, often pets will also have a skin infection on top of this, causing even more problems.

How does an allergy cause a skin infection?

With allergies in people, we usually see a runny nose, itchy/red eyes and sneezing. However, pets will react very differently.  The process goes something like this:

  • An allergen such as pollen will enter their system
  • The immune system incorrectly identifies the pollen as a threat and “overreacts,” calling in the troops. A variety of immune system cells come to the battlefield; the most important of which is the Mast Cell
  • Mast cells produce histamine, which among other things, cause itchiness and cause the blood vessels to dilate and become leaky (in the ears, this creates a hot humid environment – perfect for growing bacteria)
  • Pets are itchy and uncomfortable – as a result they will lick and chew; introducing bacteria to their skin, resulting in a skin infection

What are the signs of a bacterial skin infection?

The following are things we commonly see:

  • Papules or pustules: these are red, raised bumps that arise on the surface of the skin. They may be yellow/tan in color – these contain pus and we call them pustules (see below)

image source:

  • If these papules or pustules rupture or break open, they will form crusts, which you can easily feel – they have a rough, uneven surface and are about the same size as papules/pustules
  • Epidermal collarettes: these are areas where there is a circular area of peeling skin (see below) 


  • Hair loss: this often results from infection of the hair follicles 
  • Cats can have all of the above as well, although some cats will just have excessive grooming – as a result, they will have patchy areas of hair loss

What causes bacterial skin infections?

The most common cause is allergies! Allergies are caused by one of three things:

1.  Fleas

  • “But I don’t see any fleas on my pet.” – Dogs (and cats!) can have what we call a Flea Allergy Dermatitis, where the bite of even a single flea can cause them to be uncontrollably itchy.
  • It is very important that your pet be on year-round flea prevention, especially in California, where our temperatures rarely drop low enough to kill off the flea population. For pets that are extremely sensitive to fleas, we may need to switch them to Comfortis, which is the newest (and most effective) flea preventative on the market.

2.  Environment – pets can be allergic to pollens, dust mites, even human dander! We also refer to this as Atopy, or atopic dermatitis. This is genetic (something they’re born with). 

3.  Food – if dogs are food allergic, the allergy will be to the major protein or carbohydrate source in the food (i.e. chicken, beef, fish, wheat, soy). Food allergies can cause the same irritated skin symptoms as flea and environmental allergies.

Is there a cure?

Unfortunately, we cannot cure allergies. However, we can manage them to keep your pet more comfortable. We often can also help to lengthen the interval between skin and ear infections.

There are 6 options for managing allergies:

  • Do nothing. We will treat each skin infection as it comes along, often with the combination of antibiotics and steroids. 
  • Antihistamines: Benadryl is typically started first, as it is over-the-counter, safe, and inexpensive. However, it is important to know that very few allergic animals will respond to Benadryl alone. We have recently had much more success with Zyrtec or Claritin. Benefits of these are that they are non-drowsy and only given once a day. It is important to only use these medications if you have been directed to by your veterinarian.
  • Combination antihistamine + steroid (Temaril-P): putting an antihistamine together with a steroid allows us to minimize the amount of steroid we are administering to your pet (and hence, fewer side effects and long-term effects).
  • Allergy testing and allergy shots: we can run either blood or skin tests to determine which specific allergens your pet is sensitive to, and then combine these allergens into a shot, which you can learn how to administer at home to de-sensitize them. This can be done at Bishop Ranch Veterinary Center or with a boarded veterinary dermatologist (specialist). 
  • Immunosuppressive medications: Prednisone or Cyclosporine. Since allergies are the immune system over-reacting, we place allergic animals on steroids to minimize that overreaction. Long-term steroids do come with their risks, so it is important to weigh the pros and cons with your veterinarian before pursuing this option. 
  • The only way to diagnose a food allergy is to place your pet on a diet with a protein and carbohydrate source they have never eaten before. Veterinarians will either reach for hypoallergenic diets (i.e. Royal Canin duck and potato) or hydrolyzed protein diets (i.e. Hill’s z/d). Through the UC Davis Nutrition service, we can help you to formulate a home cooked diet if you prefer to do that. Your pet must be on this diet exclusively (no treats, rawhides, table scraps or even beef-flavored heartworm preventatives!) for a minimum of 8 weeks before we can call it a success or a failure.

If you pet is newly diagnosed as an allergic dog, you should prepare yourself. He/she will likely have a number of skin/ear infections over the course of their lifetime. It can be a long, frustrating process; however we can work together with you to find the therapy best suited for your furry friend.

Dr. Wong is a graduate of the Veterinary School at Cornell University in Ithaca, NY. Prior to veterinary school she completed her undergrad at UCLA and graduated magna cum laude with a B.S in Ecology, Behavior, and Evolution. She spent time in the rainforests of Nicaragua studying the poison dart frog and also spent three months living and working in rural villages in Tanzania with the non-profit Support for International Change. Dr. Wong completed a rotating internship at VCA West LA in Los Angeles and her special interests include soft tissue and orthopedic surgery as well as emergency medicine and dentistry. She is a San Ramon native and loves to spend time outdoors running, surfing, snowboarding, hiking, and kayaking.


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