Allergies in Dogs: General Information

Sneezing, Itching, Scratching?

One of the most common conditions affecting dogs that we see at the Animal Hospital at Thorndale is allergy. In the allergic state, the dog’s immune system “overreacts” to foreign substances (allergens or antigens) to which it is exposed. These overreactions are manifested in three ways.

1. The most common is itching of the skin, either localized (one area) or generalized (all over the dog).
2. Another manifestation involves the respiratory system and may result in coughing, sneezing, and/or wheezing. Sometimes, there may be an associated nasal or ocular (eye) discharge.
3. The third manifestation involves the digestive system, resulting in vomiting or diarrhea.

Types of Allergies in Dogs

There are five known types of allergies in the dog: contact, flea, food, bacterial, and atopic (previously called “inhalant”). Each of these has some common expressions in dogs, and each has some unique features.

Contact Allergy

Contact allergy is the least common of the five types of allergy. It results in a local reaction of the skin. Examples of contact allergy include reactions to flea collars or to types of bedding, such as wool. If the dog is allergic to such substances, there will be skin irritation and itching at the points of contact. Removal of the contact irritant solves the problem. However, identifying the allergen can require some detective work.

Flea Allergy

Flea allergy is common in dogs. A normal dog experiences only minor irritation in response to flea bites, often without any itching. On the other hand, the flea allergic dog has a severe, itch-producing reaction when the flea’s saliva is deposited in the skin. Just one bite causes such intense itching that the dog may severely scratch or chew itself, leading to the removal of large amounts of hair. There will often be open sores or scabs on the skin which allows for a secondary bacterial infection to begin. The area most commonly involved is over the rump (just in front of the tail). The most important treatment for flea allergy is to remove all fleas from the dog. Therefore, strict flea control is the backbone of successful treatment. Unfortunately, this is not always possible in warm and humid climates, where a new population of fleas can hatch out every 14-21 days. When strict flea control is not possible, antihistamines of corticosteroids (or “cortisone” or “steroids”) can be used to block the allergic reaction and give relief. This is often a necessary part of dealing with flea allergies. Fortunately, dogs are more resistant to the side-effects of steroids than humans, so much of what you know about the side-effects in people does not apply to dogs. If a secondary bacterial infection occurs, appropriate antibiotics must be used as well.

Bacterial Allergy

Staphylococcus (Staph) is a bacterium found on normal dog skin. If the skin is normal and the dog’s immune system is normal, Staph causes no problems to its host. However, some dogs develop an allergy to this bacterium. When this happens, the dog develops areas of hair loss that look much like ringworm. They are often round and 1/2 to 2 inches in diameter. These same lesions develop in true Staph infection; they are easily treated with certain antibiotics, but the Staph-allergic dog has recurrent “Staph infections.” The lesions will usually clear with appropriate antibiotics but return as soon as antibiotics are discontinued. After a while, some dogs become resistant to antibiotic treatment. Treatment of Staph allergy involves antibiotics to control the immediate problem and desensitization with Staph antigen for long-term relief.

Atopy

The most common type of allergy is atopy. This used to be considered “inhalant allergy” but now appears to be more complex. Atopy appears to be hereditary, but involves many genetic variables. The result is a failure of the dog’s immune system to respond properly to allergens and a dysfunctional skin barrier. Dogs may be allergic to all of the same inhaled allergens that affect humans. These include tree pollens (cedar, ash, oak, etc.), grass pollens (especially Bermuda), weed pollens (ragweed, etc.), molds, mildew, and the house dust mite. Many of these allergies occur seasonally, such as ragweed, cedar, and grass pollens. However, others are with us all the time, such as molds, mildew, and house dust mites. When humans inhale these allergens, we express the allergy as a respiratory problem; it is sometimes called “hay fever.” The dog’s reaction, however, usually produces severe, generalized itching. In fact, the most common cause of itching in the dog is atopic allergy. Most dogs that have atopic allergy react to several allergens. If the number is small and they are the seasonal type, itching may last for just a few weeks at a time during one or two periods of the year. If the number of allergens is large or they are they are present year-round, the dog may itch constantly. Treatment depends largely on the length of the dog’s allergy season. It involves several approaches:

1. Anti-inflammatory. Anti-inflammatory therapy will dramatically block the allergic reaction in most cases. Steroids may be given orally or by injection, depending on the circumstances. Steroids have a number of potential side effects, so the choice to use them needs to be made with a careful examination of your dog’s overall health. If steroids are appropriate for your dog, you will be instructed in their proper use. Antihistamines can be of value in treating the allergic dog when they are combined with steroids. In some dogs, antihistamines can significantly decrease the amount of steroid needed to provide relief. Fatty acid supplementation can also be implemented with steroids and antihistamines. When the three of them are combined, most allergic dogs are significantly improved. This is a non-specific approach which does not treat the allergy, only the symptoms of the allergic state (itching). Medications, such as Apoquel, target the specific “itch” factors and can provide immediate relief for some patients.
2. Topical therapy. Many dogs are helped considerably by frequent bathing with a hypoallergenic shampoo. It has been demonstrated that some allergens may be absorbed through the skin. Frequent bathing is thought to reduce the amount of antigen exposure through this route. In addition to removing surface antigen, bathing alone will provide some temporary relief from itching and may allow the use of a lower dose of steroids or antihistamines. Topical steroids, antibiotics, and antiseptics may also be utilized and have the benefit of fewer side effects than oral medications. Spot-on products which improve the skin phospholipid barrier are also having some success in some patients.
3. Hyposensitization. The third major form of allergy treatment is hyposensitization with specific antigen injections (or “allergy shots”). Once the specific sources of allergy are identified, very small amounts of the antigen are injected weekly. The purpose of this therapy is to reprogram the body’s immune system. It is hoped that as time passes, the immune system will become less reactive to the problem-causing allergens. If hyposensitization appears to help your dog, injections will continue for several years. For most dogs, a realistic goal is for the itching to be significantly reduced in severity; in some dogs, itching may completely resolve. Generally, steroids are only used on a brief and intermittent basis. This therapeutic approach is recommended for the middle-aged or older dog that has year round itching caused by inhalant allergy. This approach is not successful with food allergy.

Although hyposensitization is the ideal way to treat inhalant allergy, it does have some drawbacks that may not make it the best choice in certain circumstances for these reasons:

1. Cost: This is the most expensive form of treatment.
2. Age of Patient: Because many dogs develop additional allergies as they get older, young dogs may need to be retested 1-3 years later.
3. Success Rate: About 50% of dogs will have an excellent response. About 25% get partial to good response. About 25% get little or no response. The same statistics are true for people undergoing desensitization.
4. Food Allergies: Although tests for food allergy are available, the reliability of the test is so low that it is not recommended at this time. A food trial remains the best diagnostic test for food allergy.
5. Time of Response: The time until apparent response may be 2-5 months, or longer.
6. Interference of steroids with testing: Dogs must not receive oral steroids for 2 weeks or injectable steroids for 6 weeks prior to testing; these drugs will interfere with the test results.

Food Allergy

Dogs are not likely to be born with food allergies. More commonly, they develop allergies to food products they have eaten for a long time. The allergy most frequently develops in response to the protein component of the food such as beef, pork, chicken, or turkey. Food allergy may produce any of the clinical signs previously discussed, including itching, digestive disorders, and respiratory distress. We recommend testing for food allergy when the clinical signs have been present for several months, when the dog has a poor response to steroids, or when a very young dog itches without other apparent causes of allergy. Testing is done with a special hypoallergenic diet. Because it takes at least 8 weeks for all other food products to get out of the system, the dog must eat the special diet exclusively for 8-12 weeks (or more). If a positive response occurs, you will be instructed on how to proceed. If the diet is not fed exclusively, it will not be a meaningful test. We cannot overemphasize this. If any types of table food, treats or vitamins are given, these must be discontinued during the testing period. There may be problems with certain types of chewable heartworm preventative, as well. Your veterinarian will discuss this with you. Because dogs that are being tested for inhalant allergy generally itch year round, a food allergy dietary test can be performed while the inhalant test and antigen preparation is occurring.

Summary

Perhaps the most important thing to remember is that, just as in humans, allergies in dogs are not curable. However, they are manageable and controllable and your dog certainly can have a much more comfortable life. Understanding the different types of allergies helps with the detective work. Keep tract of seasonal changes in your dog’s itching. Think of any detergents, cleaning agents or other chemicals your dog may have contact with. Work on flea control. Allergies tend to be cumulative. There is a threshold of allergen exposure above which one reacts. They can also appear in combinations, such as food and atopic allergies. Keeping in contact with your veterinarian through the diagnostic and treatment process are essential to success in controlling your dogs allergies.