Allergies are a common and often frustrating problem for pets and pet owners alike. This handout is designed to provide owners with more information about the two main types of allergies in pets: environmental allergies and food allergies.
What are Animal Allergies?
An allergy is a state of hypersensitivity in which exposure to a harmless substance known as an allergen stimulates the body’s immune system to “overreact.” People with allergies usually have “hay fever” (itchy eyes, runny nose, sneezing, etc.) or asthma.
While dogs can sometimes have these respiratory symptoms, more commonly they experience allergies in the form of itchy skin. This causes the pet to lick, scratch, and chew various parts of their body in an effort to find relief. Owners may notice in their pets the following signs: red skin, hair loss, open sores, and/or recurring skin or ear infections.
The vast majority of pets with allergic skin disease also have accompanying bacterial or yeast skin and/or ear infections. These infections can cause an increase in the pet’s itchiness and must be addressed along with the allergy in order to give the pet relief. Treatment with antibiotics and ant-fungal medications is commonly required in allergic pets.
Environmental Allergies (Also Known as Atopic Dermatitis or “Atopy”)
Atopic dermatitis is an inherited predisposition to develop skin problems from exposure to a variety of commonplace substances including:
- House dust mites
- Mold spores
This is the canine version of hay fever. Unlike humans with hay fever, dogs usually develop intensely itch skin rather than the respiratory symptoms we usually associate with hay fever. Symptoms usually develop between 1-3 years of age.
The majority of dogs with environmental allergies are sensitive to a number of environmental allergens, not just one. In the beginning, a pet’s allergy is often seasonal, confined to once season of the year when plants and molds are actively releasing their pollens and spores. However, over time, the allergy usually becomes chronic with year-round symptoms.
Heredity plays a role in this type of allergy, as genetic susceptibility can be passed from parent to puppy. Because of the genetic nature of the problem, it is important to understand that allergies can be controlled, but not cured.
Some pets develop specific hypersensitivities to components of their pet food. The allergen is usually a major protein or carbohydrate ingredient, such as beef, chicken, pork, corn, wheat, or soy. Minor ingredients such as preservatives or dyes are also potential allergens.
For some reason, these certain ingredients are recognized by the immune system as something to be attacked. The resulting inflammation may target the digestive tract, but most commonly affects the skin.
Many people assume that itching due to a food allergy requires a recent diet change of some sort. In fact, the opposite is true. Food allergies take some time to develop, and most pets have been eating the offending food for a while with no trouble. Dogs can develop an allergy at any time to any type of food.
The clinical signs of food allergies are identical to those symptoms of environmental allergies. However, a pet with food allergies is itching year-round; it’s not just a seasonal problem.
Can Allergies be Cured?
Unfortunately, there is no cure for allergies and they are usually life-long problems. However, there are a variety of treatment options, including oral medications, topical products, and/or diet changes, that may provide relief. This can greatly improve the quality of life for both you and your pet. Your veterinarian can help you formulate a specific treatment plan for your pet.
There are two approaches to treating allergies in pets. In pets with mild allergies, we can sometimes control the symptoms with medication. This is a safe option if the pet’s itching can be controlled with medications such as antihistamines that have relatively few side effects. The itching can also be controlled with a short course of medication such as steroids during the worst part of the pet’s allergy season. However, allergies tend to become more severe and more chronic over time. In these cases, it is often necessary to determine what exactly the pet is allergic to in order to treat the underlying cause.
Treating the Symptoms
Steroids, such as prednisone, are often used as the first line of defense against itchy skin. However, without address the underlying cause, the itching will eventually return. In addition, long-term use of steroids can result in a variety of health problems. Side effects of chronic steroid use include the following:
- Excessive thirst
- Excessive appetite and subsequent weight gain
- Urinary incontinence (i.e. leaking urine)
- Lethargy and/or panting
- Muscle break down
- Suppression of the immune system
- Inflammation of the pancreas
- Development of diabetes
If your dog requires steroid therapy more than 2-3 months out of the year, you should consider the following:
- Further testing to determine what exactly your pet is allergic to in order to develop a more specific treatment plan
- Alternative therapy with antihistamines, fatty acid supplements, etc.
- Referral to a veterinary dermatology specialist
If continued, steroid use is the only way to keep your pet comfortable. It is important to regularly monitor your pet’s response to steroids with periodic blood work, urine tests, and/or re-examination by your veterinarian.
Treating the Underlying Cause: Environmental Allergies
The classic test to determine what in the environment a pet is allergic to is skin testing, which is usually performed by a veterinarian dermatologist. This involves making small injections in the skin with a variety of different allergens. If the pet is allergic to any of these substances, a small red welt will appear at the injection site. However, before skin testing can be done, the pet must be off all medications such as steroids and antihistamines for a certain period, which can be difficult to achieve in an allergic pet. The alternative to skin testing is a blood test that analyzes the blood to determine what the pet is allergic to.
The purpose of either skin testing or blood work is to formulate individual allergy shots for the pet. Although most veterinary dermatologists believe that allergy shots (also known as hyposensitization) based on skin testing works somewhat better than allergy shots based on blood work, either is preferable to long term steroid use.
Once the skin testing or blood work results have been analyzed, allergy shots can be developed for the pet. The pet is given increasing doses of selected allergens, by injection, over a period of months. This alters the pet’s immunologic response, which reduces or eliminates the sensitivity to the allergens.
Approximately 75-80% of animals that go through hyposensitization treatment show improvement. However, allergy shots do not immediately “fix” the problem. It is important to note the following:
- Allergy shots require ~6-12 months to reach full effectiveness.
- 25% of dogs will require additional medications at least some of the time.
- 25% of dogs will not respond significantly.
Thus, even with allergy shots, other medications (such as short courses of steroids, antihistamines, etc.) may be necessary to control the pet’s allergy symptoms. In addition, antibiotics, anti-fungals, and medicated baths at the time of flare-ups may be necessary to control secondary skin infections.
It is often useful to rule out food allergies with a food trial (described below) prior to allergy shots as food allergies respond much more rapidly to diet correction than environmental allergies do to allergy shots.
Treating the Underlying Cause: Food Allergies
Diagnosing a food allergy requires a food trial, which involves feeding the pet a hypoallergenic diet for at least 2 months. The diet must contain ingredients that your pet could not possibly have developed an allergic response to, meaning ingredients your pet has never been exposed to.
The traditional approach for food trials is feeding a novel protein and carbohydrate source, such as venison and potato, fish and potato, egg and rice, duck and pea, etc. Another approach is using a food made from hydrolyzed proteins. This means that a convention protein source is used, but the protein is broken down into molecules too small to stimulate the immune system.
Whatever type of food is chosen, it is critical that during the food trial nothing other than the prescribed food cross your pet’s lips! This means no edible chew toys (such as rawhides or bones), no unauthorized treats, and no table scraps. Chewable heartworm preventative (which often contains beef) should be replaced with non-chewable tablets or topical preparations (such as Revolution).
Eighty percent of food allergic dogs will have responded to the food trail at least partially by six weeks. Some breeds, such as Labrador retrievers and cocker spaniels, may require up to 10 weeks before showing a response. Some individuals may require even longer.
If the signs resolve, a “challenge” is performed by feeding the previous diet to see if the itching returns. If the itchiness does return (usually within 2 weeks), a diagnosis of food allergies is confirmed. Many owners don’t want to risk the return of clinical signs if the pet is doing well; it is not unreasonable to simply stay with the test diet if the pet remains free of symptoms.
Allergies: Alternatives to Steroids
Excessive licking, chewing, and scratching can make a pet’s life miserable. For rapid relief of itch and inflammation, nothing matches corticosteroids such as cortisone, prednisone, and others. Unfortunately, these drugs have potentially harmful side effects when they are used inappropriately for long periods. Ideally, corticosteroids are reserved for a few itchy weeks and other forms of itch management are used for longer periods to keep the pet comfortable. The following list includes various alternatives for relieving itch and/or reducing the amount of corticosteroids needed.
Histamine (a biological chemical) is the chief mediator of inflammation in humans, hence the wide variety of antihistamines available. However, histamine is not the major mediator of inflammation in dogs, thus these medications are not as reliable for dogs as they are for humans. It is estimated that only 10-20% of dogs will respond to any given antihistamine.
To determine if antihistamines will help your pet, we recommend an antihistamine trial. This involves using several different antihistamines (one at a time) for at least 2 weeks each in hope of finding one that works for your pet. Some examples of antihistamines include the following:
- Diphenydramine (Benadryl)
- Hydroxyzine (Atarax)
- Chlorpheniramine (Chlor-Trimeton)
- Clemastine (Tavist)
While antihistamines are not completely free of side effects (the most common side effect being sedation), they have far fewer systemic side effects compared to corticosteroids.
Fatty Acid Supplements
The discovery of anti-inflammatory properties of fish oils in humans has led to similar products on the market for pets. These specific fatty acids disrupt the production of inflammatory chemicals within the skin. When used alone, fatty acid supplements are effective in ~10% of itchy dogs; thus, they are often used in combination with antihistamines to boost the effectiveness of both.
Cyclosporine (also known as Atopica)
Cyclosporine is an immune modulating drug, meaning it decreases the abnormal immune reaction in allergic animals. Cyclosporine was investigated as an alternative to corticosteroids and found effective in many patients. Veterinary dermatologists consider this product a true breakthrough in reducing the need for steroids. Cyclosporine is more expensive than steroids, but does not lead to long term debilitating side effects as steroids can. Short-term side effects include stomach upset when starting the drug. This side effect generally resolves with time or is managed with dose modification.
A relatively new medication used by many dermatologists across the nation, this medication is not as expensive as cyclosporine and seems to be fairly effective in many cases. This medication interrupts the ‘itch cycle’ to help stop itching in its tracks.
Many allergic dogs have excess oil accumulation and/or secondary skin infections, which also contribute to itchy skin. A medicated shampoo may be prescribed to address any of these conditions. Ten minutes of skin contact is the minimum requirement for any medicated shampoo. Premature rinsing decreases the effectiveness of these products. When using any shampoo on inflamed skin, the use of cool water is considered more soothing than warm water.
Oatmeal Shampoos, Sprays, and Lotions
Oatmeal acts to pull inflammatory toxins out of the skin, generally yielding 1-3 days of relief. These products are available plain or combined with local anesthetic formulas to further soothe the itch.
Topical steroids, such as cortisone crèmes and related products, are absorbed through the skin and into the bloodstream, but the side effects with topical use are less severe. For small irritated areas, such as “hot spots,” topical steroids can provide excellent relief without the systemic effects of oral steroids. However, topical steroid preparations are not effective for widespread areas of itchiness.
Aloe Vera Gel
Aloe vera gel contains enzymes, which break down inflammatory proteins and enhance healing. If possible, obtain 100% aloe vera gel from a health food store. Products labeled as containing “aloe” are more widely available, but are not as effective and not meant to be licked away by a pet. Pure aloe vera gel is not harmful to pets who may lick it off.
This product has a cooling effect on the skin that is soothing for both animals and for people with sunburns. It is available as a spray or lotion.
Steroids as a Last Alternative
Although steroids can have harmful long-term results, they are also very effective medications when used appropriately. The goal is not to avoid steroid use at all costs, but to avoid long-term dependence of steroids if possible. Despite all of the above alternatives, some pets will still require long-term steroid use to achieve any reasonable comfort. In these cases, it is important to regularly monitor your pet’s response to steroids with periodic blood work, urine tests, and/or re-examination by your veterinarian.