Like humans, dogs can have allergic reactions, too. The signs of allergies in dogs can vary broadly. At first glance, you might not know if your dog has seasonal allergies, food allergies, or something else.
Not all allergies show up the same way. Understanding the signs of allergies in dogs can help reveal possible solutions, including whether to reach for over-the-counter medications or consult your veterinarian. It’s important to rule out other underlying conditions, such as skin parasites, before treating a dog for allergies.
Canine allergies can range from mild discomfort to life-threatening, so the sooner a dog gets a diagnosis and treatment, the sooner they can feel better.
What is an allergy?
An allergy starts with an allergen—usually a foreign substance or food. Allergens are substances that stimulate the immune system, causing the body to release a chemical called histamine. That release of histamine results in inflammation, which triggers the clinical signs usually associated with allergic reactions (like redness, swelling, and itching).
Why dogs get allergies
Allergies are multifactorial, meaning they have both genetic and environmental risk factors. Each type of risk factor contributes to the allergic response in different ways. Environmental risk factors (allergens) are required for allergies to occur, but it’s the genetic risk factors that are responsible for ramping up a dog’s immune system.
Such genetic risk factors can play a role for an individual dog or entire breeds. Allergic diseases can run in families, making genetic history important both for breeding decisions and for a dog’s individual medical history. While we don’t offer a genetic test specifically for predisposition to allergies, knowing your dog’s genetic history is a tool that can help you be prepared. Learn more about how Embark testing relates to allergies.
Which allergies are most common in dogs?
In dogs, allergies come in three main forms: flea, environmental (sometimes called atopy), and food.
- Flea allergies are the most common canine allergy and can happen anywhere there are flea populations. They can also occur any time of year. As little as one flea bite can trigger this response.
- Environmental allergies can be seasonal and peak at specific times of year, especially spring and summer. Exposure to these allergens occurs via skin contact or inhalation. Environmental allergies can also be caused by indoor and non-seasonal substances, such as dust mites, molds, and many others. Skin contact allergies are less common. These allergies can be due to ingredients in medication, hygiene products, fabrics, or something else. For contact allergies, a dog would likely show redness or irritation of the skin.
- Food allergies result when the body has an abnormal response to any food component.
Types of canine allergies
Insects, including fleas, can cause dermatitis with severe itching. For some dogs, though, flea bites can lead to canine flea allergy dermatitis (FAD). FAD in dogs is due to hypersensitivity to substances in flea saliva, and it can cause severe skin reactions long after the flea has jumped off.
Flea allergy dermatitis is the name of the skin irritation that occurs in response to a flea bite in allergic dogs. Spotting fleas or flea dirt helps with the diagnosis, but sometimes, a dog can develop signs of flea allergy dermatitis from one brief flea bite. Recent history of dog parks, boarding, grooming, or interaction with other animals could make flea exposure more likely.
Environmental allergies can be difficult to determine, but sometimes it helps to pay attention to whether they are seasonal or year-round. Like people, dogs have mast cells in their skin that store histamines for a quick immune response to an allergen. Although some dogs react to seasonal allergens with a runny nose or sneezing, they are much more likely to get itchy skin.
Environmental allergies in dogs can happen from a variety of indoor and outdoor allergens. Some of them include:
- Insect bites
- Tree pollen
- Grass pollen
- Flower and weed pollen
- Dust and dust mites
- Mold spores
Atopic dermatitis is an inflammatory, chronic skin condition associated with environmental allergies. It is influenced by both genetic and environmental factors. By one estimate, atopic dermatitis affects 10 to 15% of dogs.
Some breeds appear to be affected by atopic dermatitis more frequently. These breeds include Golden Retrievers, Labrador Retrievers, Dalmatians, Scottish Terriers, French Bulldogs, West Highland White Terriers, Boxers, Chinese Shar-Peis, Lhasa Apsos, and German Shepherds.
Allergy testing can be used to determine the underlying environmental trigger that a dog is reacting to. The two main types of allergy testing are 1) intradermal (skin) and 2) serum (blood).
Dogs can also have allergies to components in food (sometimes called adverse food reactions). If a dog is allergic to a type of food, they can show skin reactions, gastrointestinal reactions, or both.
Like canine atopic dermatitis, food allergies are caused by an abnormal reaction of the immune system to a substance. While the cause of food allergies is not completely understood, it does require a dog to be exposed to the allergen.
A review of several studies determined that the most common ingredients responsible for food allergies in the studied dogs were beef, dairy, chicken, and lamb. Wheat, soy, and corn were the most common plant-based ingredients implicated in food allergies; however, allergies to these three ingredients were less prevalent than the four common meat-based allergies.
If a food allergy is suspected, your veterinarian may discuss performing a strict food trial, which is currently the only reliable way to diagnose a food allergy. Unfortunately, skin and blood tests are not proven to be reliable ways to diagnose food allergies at this time. Once a food allergy is identified, your vet may recommend certain dog foods.
Food allergies vs. food intolerances
When looking for the cause of a dog’s allergic reaction, people commonly interchange food allergies and food intolerances. There are some key differences between these two reactions.
While food allergies occur due to an abnormal immune response, food intolerances do not involve the immune system. Another key difference is that dogs can show intolerance to a food or ingredient the first time they eat it, whereas they need at least one prior exposure to a food to develop a food allergy.
Common food intolerances could include eating:
- Too much of one nutrient
- A diet with too much fat
- A poisonous or irritating food, like chocolate or rhubarb
- Foods with additives
- Foods with lactose
Signs that a dog is having an allergic response
The following five signs may indicate that your dog is having an allergic reaction.
1. Skin issues: itching, excessive licking, red and inflamed skin, and hot spots
A dog who is itching on their face, belly, groin, rear, base of their tail, or side could be showing signs of an allergic response. Because itching can be a sign of atopic dermatitis, food allergies, and flea allergies, this alone does not help us identify the allergen. The location of itchiness can give clues—for example, itching primarily on the back and base of the tail could hint at a flea allergy.
Excessive licking due to itchiness is one of the most consistent symptoms of dog allergies. It can happen with all allergy types, and it can become so intense that it causes hair loss, bald spots, and areas of raw skin. Excessive licking of the feet, rear end, and inner thighs is particularly common.
Irritated skin quickly turns red and inflamed, and it can feel warm to the touch. Dogs can get red, inflamed skin from any allergy. However, if itchiness is causing them to lick, bite, or scratch at themselves excessively, the skin may also become traumatized, leading to more significant medical issues.
Hot spots (also known as pyotraumatic dermatitis) are moist, itchy, and painful lesions seen in some allergic dogs. Although allergy-related itchiness is likely an inciting factor, self-trauma to relieve the itch plays an important role in hot spot formation. Hair loss is often evident at the site of the lesion and surrounding hair is commonly matted with dried pus. If left alone, hot spots may dry up, scab and heal. However, hot spots commonly result in a recurring cycle of itch and self-trauma, making resolution challenging in some cases. Secondary infections of hot spots are also common and may require antibiotic therapy.
To treat or prevent these lesions, it’s important to stop your dog from traumatizing the hot spot any further. Next, consult your veterinarian to determine the underlying cause.
2. Repeated ear infections
Ear canals are essentially modified skin. Repeated ear infections are a common indication of an underlying sensitivity to food or something in the environment.
3. Red, runny eyes
Red and runny eyes can happen due to certain environmental allergies when allergens are airborne. If your dog develops yellow or green discharge from their eyes, has crusty and swollen eyes, or is squinting or pawing at their eyes, contact your veterinarian.
4. Vomiting and diarrhea
Vomiting and diarrhea are common signs of food allergies in dogs. Some dogs may also exhibit gastrointestinal noises, flatulence, and soft stools. Dogs can also develop vomiting and diarrhea from dietary indiscretion when they eat something they shouldn’t, but this is not considered an allergic response.
5. Swelling and hives
Dogs with more severe, acute allergic reactions can get swelling and inflammation on the face, ears, paws, eyelids, muzzle, or lips. This swelling is a direct result of the histamines released and can happen from many types of allergies. If you see swelling on your dog’s face, contact your veterinarian as soon as possible.
Hives look more like a rash with raised bumps, and they can appear in response to lots of triggers, including insect bites, medications, foods, and more. In dogs, hives might be the only sign or they can be associated with a more severe systemic allergic reaction, called anaphylaxis. If you notice hives, contact your veterinarian.