Allergy in Dogs: Atopy

At the Animal Hospital at Thorndale, one of the most common conditions affecting dogs 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. The most common is itching of the skin, either localized (one area) or generalized (all over the dog). 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. The third manifestation involves the digestive system, resulting in vomiting or diarrhea.

Types of Allergy

There are five known types of allergies in the dog: contact, flea, food, bacterial, and atopy (previously considered “inhalant allergy”). Each of these has some common expressions in dogs, and each has some unique features. The remainder of this article discusses Atopy.

Important Concepts

1. Perhaps the most important thing to keep in mind is that allergies cannot be cured, in humans or in dogs. They can be controlled and life made more comfortable.
2. Another concept is that allergens are cumulative. There is a threshold of exposure above which you start to have problems. That is why pollen counts help people determine which days will be good or bad days of exposure. If your dog has pollen allergies, those pollen counts may also indicate how itchy he will be.
3. Multiple allergies can push you over the threshold even at lower individual allergen counts. Consider the threshold an invisible line above which your allergies act up. A heavy dose of a single allergen or moderate doses of multiple allergens can all add up to push you above that threshold.
4. If you have allergies, you tend to become allergic to additional things as you go through life. The same is true for our pets.

Atopic Allergy

The most common type of allergy in dogs is atopy. Atopy was once considered “inhalant allergy” but now appears to be more complex. There is a hereditary predisposition to developing atopy, but the genetics appears to be complex. The result is an inability of the dog’s immune system to regulate its response to certain allergens and a failure of the skin barrier to prevent these allergens and microbes from entering into the dog. 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, other allergens are with us all the time, such as molds, mildew, and house dust mites.

When humans inhale allergens, we express the allergy as respiratory problems. These include coughing, sneezing, a runny nose, and watery eyes. The dog’s reaction, however, usually produces severe, generalized itching. It will chew, lick, or scratch almost any area of the body, including the feet. Chewing and scratching produce hair loss and inflamed areas of the skin. Saliva will stain light colored hair, so dogs that lick excessively will have orange or reddish brown hair. This is often seen on the feet. Although most people think that itching is related to fleas, the most common cause of itching in the dog is atopic allergy. The reason we wheeze and sneeze and dogs itch has to do with where the allergy reactive cells are most concentrated in the body. In dogs, most of the allergic reactive cells are in the skin. Therefore, unlike humans, dogs itch when they have a pollen, dust, or mold allergy.

Determining the Cause

Determining the offending allergen is not something that we can do easily. The itching produced by ragweed allergy is the same as that produced by oak pollen allergy. In other words, an individual animal or person can be allergic to many different things with the end result (itching) being the same. In some cases, allergy testing can make specific determinations, and sometimes an educated guess can be accurate if the itching corresponds with the blooming season of certain plants. However, it is not always necessary to know the specific allergen for treatment to be successful.

Seasonal vs. Year Round Allergy

As the names imply, some dogs only have allergic reactions during specific periods of the year while others will itch year round. A year round allergy occurs for two reasons. First, the allergen is present year round. This is the case for indoor dogs that are allergic to house dust mites, also known as “house dust.” Second, the dog is allergic to so many things that at least one of those allergens is present at all times.

Even though many dogs begin with allergies on a seasonal basis, they often evolve into a year round basis. With the passage of time, it usually becomes allergic to more and more things. After several years of acquiring new allergies, it reaches the point that it is constantly exposed to something to which it is allergic.

Some year round allergies may actually be due to food allergies, because the dog is eating the same food year round. Read more about food allergies.

Grass Allergy

Dogs that are allergic to “grass” are really allergic to grass pollen, not to the grass itself. The blades of grass will cause no harm to your dog so walking in it is not a problem. Bermuda grass is the most allergenic grass because it releases so much pollen into the air. Keeping it mowed so it does not pollinate seems logical, but your neighbors must do the same because the pollen is airborne. The same principle applies to trees. Dogs are not allergic to the wood of a certain tree, only to its pollen.

Treatment Options

Our recommendation for treatment depends largely on the length of your dog’s allergy season and involves four approaches:

1. Anti-inflammatory drugs. Anti-inflammatory therapy will dramatically block the allergic reaction in most cases. Steroids (“cortisone”) may be given orally or by injection, depending on the circumstances. Because steroids have a number of side effects, careful consideration of your dog’s overall health must be made when deciding to use steroids. 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 and can be combined with steroids if necessary. 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 result of the allergic state (itching). Medications, such as Apoquel, can directly target the “itch” pathways and can provide immediate relief in some patients. If drugs such as Apoquel are successful, steroids may be completely eliminated from the treatment regimen.
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 oral medications. Some of the hypoallergenic shampoos incorporate fatty acids; these may be absorbed through the skin and offer a localized anti-inflammatory action. The role of the fatty acids in allergy treatment is an area of active research interest in veterinary medicine. There are a number of leave-on conditioners and spot-on fatty acid products available that may help significantly.
3. Antibiotics. Dogs that damage their skin by licking, chewing, and scratching are quite susceptible to bacterial infections in the skin. If this occurs, antibiotic should be given until the infection is controlled. The skin infection itself can be quite irritating and cause a dog to itch even more. Some dogs actually develop allergic reactions to the bacteria on their skin.
4. Hyposensitization. The fourth major form of allergy treatment is hyposensitization with specific antigen injections (or “allergy shots”). Once testing identifies the specific allergens, 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 the 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.

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

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

How Fleas Relate

A dog with atopic allergy will itch even if fleas are not present. However, if fleas are crawling around on your dog, the itching will increase. Although getting rid of all of your dog’s fleas will not stop the itching if he has atopy, it will make it much easier to control the itching successfully.

Terrible Skin Odor

There are several possible causes of odor associated with atopic allergy. These dogs are very prone to ear infections because the ear canal is an extension of the skin. When it becomes inflamed, it is easily infected. These dogs are also likely to have seborrhea. Sebum is the oily material normally produced in the skin. When a dog scratches, sebum production increases dramatically. This produces a musty odor. A bath will remove the odor, but it is gone for only a few hours. The key to controlling seborrhea is to stop the itching and scratching. Secondary skin infections with bacteria or yeast also may have an odor. These can be treated by appropriate oral medications and shampoo.

Treatment Failure

There are two scenarios in which there will be disappointing results to treatment. The first scenario is when steroid tablets are given and the response is poor. A few dogs may respond better to injectable steroids than to the oral form. Fortunately, this only occurs about 5% of the time. However, successful management of itching in those dogs will require periodic injections of steroids, if the itching cannot be controlled with other drugs or other forms of treatment. The problem with long acting steroid injections is that once in the system, they cannot be removed or taken away. Steroids can cause a number of side affects. Pills can be stopped if the side effects are noted and alternative therapies tried.

The other scenario is either a total failure to respond to injectable or oral steroids or a response to an injection is short-lived, lasting only a few days instead of a few weeks. This could occur because the dose was too low; however, it may also mean that the dog has a food allergy. A food allergy causes itching and scratching identical to inhalant allergy, but it responds very poorly to steroids. Food allergy is diagnosed with a food trial using a hypoallergenic diet.