Diarrhea, bald spots, watery eyes... Does my dog have allergies?

Allergies reduce dogs’ quality of life. Identifying and treating them, on the other hand, supports the animals’ health and wellbeing. Since dogs were first domesticated — more than 15,000 years ago — canine food allergies have increased, something for which the reason is currently unknown: “It is possible that there were fewer before since the canine diet was very limited. In the past, dogs only ate the prey they hunted, but now adverse reactions to food are increasing,” warns veterinarian Juan Antonio Aguado of the Montepríncipe Clinic in Madrid.

The signs that indicate that a dog is allergic are diverse. “It may have diarrhea, or scratch its face, ears, armpits, groin, or between its toes. In addition, there may be bald patches in these areas and the skin may be irritated,” Aguado says. The veterinarian also mentions other allergic symptoms in dogs that are important to look out for: “Fleas, dandruff, and scabs, especially on the back, as well as sneezing frequently or watery and rheumy eyes.”

Dogs, like humans, can suffer from various types of allergies. The ones that Juan Antonio Aguado describes, from his own experience as a veterinarian, are the main types:

• Skin allergies, known as allergic dermatitis. These are caused by pollen, dust, or some types of fungi and yeasts. Among them, allergy to flea bites is the most common in dogs and is caused by the reaction to the parasite’s saliva.
• Environmental allergies. These are not very common. They usually occur at certain times of the year, because they are seasonal, and can be brought on by pollen in the air and cause the animal to sneeze or develop conjunctivitis.
• Food allergies. Any food can trigger an allergic reaction. The symptoms can be varied, but they are almost always present on the skin, such as pruritus (itching) on the face, ears, legs, and abdomen. The dog might also have skin lesions, such as pustules and hair loss due to scratching.

Beyond the signs in the dog, dog owners should bear in mind that certain dog breeds are more predisposed to having certain allergies. In the case of food allergies, Golden Retrievers, Labradors, German Shepherds, West Highland White Terriers, Pugs, and Boxers, as well as short-haired and white-coated breeds, tend to develop them more. Aguado also points out the age at which these reactions most often develop: “It is diagnosed especially in young dogs, from six months of age, with a higher percentage around the first year of life (48%) and in older dogs.”

Furthermore, food allergies are chronic. “They are for life and can change and be caused by other foods,” adds the veterinarian. Still, some can be treated with vaccines. “They are individualized and are applied in small doses subcutaneously or orally, which allows the dog to reduce its hypersensitivity to the allergen until it can tolerate it,” he clarifies.

How allergies influence canine behavior

An allergy can alter a dog’s behavior. Unwanted behaviors such as aggression have their origin in dermatological problems and allergic reactions, especially to certain foods. “The immune system can be altered by negative emotions. There is a relationship between the psychological, immunological, and endocrine systems in the dog, and when an allergy upsets the balance between them, it is reflected in the animal’s behavior,” explains veterinarian Estefanía Pineda, who is a specialist in behavioral medicine and animal welfare, as well as a professor at the Department of Animal Production at the Complutense University of Madrid. Pineda states that the trigger is in these cases of change in the animal’s behavior is unknown: “It may be that the allergy occurs first and then there is an emotional alteration, which ends up affecting brain neurotransmission,” she clarifies.

Dogs with allergies have a greater predisposition to certain compulsive behaviors: “Chewing on objects, hyperactivity, excessive licking of the skin, and a tendency to alopecia,” the animal behavior expert continues. In addition, stress can be a trigger for dermatological and gastrointestinal allergies. “It affects the immune system because it lowers the animal’s defenses, which causes the dog to be more irritable because it is experiencing discomfort or pain, and can trigger aggressive behaviors,” the veterinarian warns. The allergic dog has less patience, so it avoids interaction with its guardians more. “It becomes a more apathetic animal; it does not want to play and, if encouraged to do so, it can react by attacking,” she adds.

Other behaviors that a dog with an allergy can develop are associated with phobias. “It may become afraid of noises, such as storms, which triggers intestinal problems. Or it may experience states of depression associated with its lowered capacity to deal with frustrating situations, such as enduring chronic pain,” adds Pineda. All of this translates into the alteration of the bond with the owner. They do not usually know the underlying reason for the dog’s behavior, until the veterinarian diagnoses an allergy. Meanwhile, the animal may appear elusive or have no appetite.

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