What is an allergy?
An allergy is a state of over-reactivity or hypersensitivity of the immune system to a particular substance called an allergen. When a dog with allergies is exposed to an allergen, their body reacts as if it is a threat. Most allergens are proteins from plants, insects, animals, or foods. Allergies are one of the most common medical conditions affecting dogs.
Allergies develop when the body mistakenly sees a harmless substance as a threat. The body sensitizes the immune system to the substance so it can respond more forcefully the next time it encounters that substance. This process is the same as how the body responds to a bacterial infection. The immune response triggers a cascade of cell activation and chemical release, leading to the allergic reaction, including swelling, redness, and itching. In more severe cases, the response may cause airway swelling, vomiting, diarrhea, and shock.
What causes the immune system to become sensitized is not completely understood, but may include:
- Genetic predisposition to sensitization
- Genetic-related defects in the external skin barrier causing more “normal substances” like pollen to penetrate deeper into the skin and more likely interact with immune cells
- Environmental pollution, including second-hand tobacco smoke
Most allergies appear after six months of age, with most affected dogs over one or two years. Some allergies are thought to be inherited, such as atopic dermatitis.
What are the symptoms of allergies in dogs?
Allergies in dogs can show up in different ways, affecting the skin, breathing, or digestion. Common symptoms include:
- Itching skin, localized to one area or all over the dog's body (most common)
- Coughing, sneezing, and wheezing
- Nasal or eye discharge
- Vomiting, flatulence, or diarrhea
What are some common allergens?
Many substances can act as allergens. Most allergens are insect, plant, or animal proteins, but small chemical molecules can also cause allergies (e.g., certain medications). The four most common types of allergies in dogs are:
- Insect bite allergy (e.g., flea bite)
- Atopic dermatitis or atopy (caused by environmental allergens, including house dust mites, pollens, and molds)
- Food allergy
- Contact allergy
These allergies have common symptoms in dogs, but each has unique features.
What is an insect bite allergy, and how is it treated?
An insect bite allergy is an exaggerated inflammatory response to the bite or sting of an insect (or arachnid). Sensitive dogs may experience an allergic reaction after being bitten by insects such as fleas, blackflies, deerflies, horseflies, mosquitoes, ants, bees, hornets, and wasps, or arachnids such as spiders and ticks.
Flea saliva is the most common insect allergen in dogs, causing flea allergy dermatitis (FAD). Most dogs experience minor skin irritation from flea bites. A dog with FAD will react to a single bite with severe local itching. This reaction is an allergic response to proteins (antigens) in the flea's saliva. One flea bite may cause such intense itching that the dog will bite and scratch itself, causing hair loss and wounds, especially around the base of the tail. A secondary bacterial infection may develop in areas where there is broken skin.
The most important treatment for flea allergy is to prevent flea bites. Strict flea control is essential. Modern monthly flea preventives and home treatment options allow you to provide a flea-free environment for your dog. Your veterinarian can advise you on protecting your dog and other pets from fleas.
When strict flea control is not possible, or in cases of severe itching, your veterinarian may prescribe antihistamines or corticosteroids (steroids) to block the acute allergic reaction and give immediate relief. If a secondary bacterial infection is present, an appropriate antibiotic will be prescribed.
What is atopic dermatitis (atopy), and how is it treated?
Atopic dermatitis, also called atopy, refers to allergic reactions to environmental allergens. The main allergens are tree pollens (e.g., cedar, ash, oak), grass pollens, weed pollens (ragweed), molds, mildew, and house dust mites. Many of these allergies occur seasonally, such as ragweed, cedar, and grass pollens. However, others occur year-round, such as molds, mildew, and house dust mites. In dogs, atopic dermatitis shows up as severely itchy skin (pruritus). Your dog may rub their face, lick their feet, and scratch their armpits and groin area.
Most dogs with atopic dermatitis start showing signs between one and three years of age. Many dogs react to multiple allergens and some may also have insect or food allergies. Most allergens are hard to avoid, and flare-ups may occur over time. Symptoms of atopy can be controlled, but a permanent cure is not typically possible.
Treatment depends largely on the length of the specific allergy season and may involve one or more of the following therapies:
Anti-Inflammatory Therapy
Medications to control inflammation and itching (e.g., corticosteroids) can quickly block the allergic reaction in most cases and are often used for sudden flare-ups.- Antihistamines can be helpful with mild symptoms.
- Fatty acid supplementation in the diet can sometimes improve the response to steroids and antihistamines.
- Newer medications block specific chemical signals associated with itch in dogs, including daily oral medications like oclacitinib (Apoquel®) and ilunocitinib (Zenrelia®), and long-acting injections, such as lokivetmab (Cytopoint®). Your veterinarian will help you determine whether these medications may be appropriate for your dog.
Topical Therapy
- Regular bathing with medicated or hypoallergenic shampoos can help soothe the skin and remove allergens from the coat.
- Some therapeutic shampoos also contain ingredients to help improve the skin barrier and decrease inflammation.
- Antibacterial or antifungal shampoos may be recommended if secondary infections are present.
- Medicated wipes, sprays, mousses, or creams can be used on problem areas or between baths.
Hyposensitization or Desensitization Therapy
If specific allergens are identified through testing, a customized allergy serum can be made for your dog (allergy shots). This serum is given in small, regular doses (oral or injection) to “reprogram” the immune system to become less reactive over time. The goal is usually to reduce itching and reliance on medications rather than eliminate symptoms entirely. Some pets show significant improvement, while others have more modest responses.
Nutritional Therapy
Some pets with atopic dermatitis also have food sensitivities. A hypoallergenic diet trial (typically 8–12 weeks) may be recommended to help identify and manage food-related allergies. Special veterinary diets may help improve skin health and reduce inflammation, which can lessen itching in some dogs. Your veterinarian can help create a nutritional plan.
What is a food allergy, and how is it treated?
A food allergy is caused by an immune reaction to a food or food additive and usually develops in response to proteins in the food (e.g., beef, pork, chicken, dairy, lamb, or soy). Vegetable proteins (glutens), such as those found in corn and wheat, and food additives and preservatives may cause food allergies in some cases.
A food allergy can develop at almost any age. Common clinical signs include itching, digestive disorders, and respiratory distress. A dog may have multiple types of allergies, such as food allergy and atopy, making it difficult to diagnose the exact cause of itching. Food allergies typically do not respond well to corticosteroids or other medical treatments. Treatment requires identifying and removing the ingredients causing the reaction.
The most accurate way to diagnose a food allergy is with an elimination diet trial using a veterinary hypoallergenic diet. This test involves feeding a special diet exclusively for 8–12 weeks, which features only new (novel) proteins or hydrolyzed proteins. During this time, your dog must eat only the prescribed diet. No treats, table food, or flavored medications are allowed, as even small amounts can affect the results. If there is a positive response and improvement in your dog’s clinical signs, your veterinarian will advise you on how to proceed.
What is a contact allergy, and how is it treated?
A contact allergy is the least common type of allergy in dogs. It results from direct contact with allergens, such as pesticides found in flea collars and on grass, materials such as wool or synthetics used in carpets or bedding, shampoos and laundry detergents.
If your dog is allergic to such substances, they will have skin irritation and itching at the contact points, usually the feet and stomach. Removing the allergen (once identified) often solves the problem, although topical or systemic treatments may be required.
Could anything else cause these symptoms?
Allergy symptoms can be confused with other disorders or occur at the same time as other disorders. For that reason, do not attempt to diagnose your dog without veterinary assistance.
- Skin symptoms can be caused by a range of issues, including flea infestations, skin mites, fungal infections (e.g., ringworm), autoimmune skin diseases, and certain cancers.
- Digestive and respiratory symptoms can be caused by many other conditions, such as infectious diseases.
Your pet needs a full diagnostic evaluation to rule out other causes of itching, skin problems, and other allergy symptoms. If an allergy is diagnosed, your whole family must follow your veterinarian's advice closely to successfully relieve your pet's discomfort.
