Allergic inflammation plays a big role in allergy reactions and contributes to the itching and chewing commonly seen with allergies. Histamine is an important part of this inflammatory process. The major source of histamine related to allergies is the mast cell. It is in body tissues like the skin, respiratory lining, and digestive tract. 

Mast cells release histamine when stimulated. Stimulation happens with certain tissue injuries and when the mast cell encounters antibodies bound to the allergen. Common allergens that the body reacts to can be found in the environment like pollen, molds, dust mites or they can be ingredients in food.

Histamine release signals cells that have histamine receptors. Binding with the receptor on the cell surface triggers a response in that cell. Depending on the body location of these receptor cells, responses can include dilation and increased leakiness of blood vessels that allows more immune cells to arrive into the affected area. Other effects include constriction of airways, mucus production, and sneezing. Interestingly, mast cells and other immune cells also have histamine receptors that help to recruit those immune cells to the affected area. This also helps expand the body’s ability to respond to tissue injury and to substances that the body has identified as foreign.

Activation of cells that have the H1 histamine receptor (there are four) in areas of the skin is inflammation and itchiness. Commonly involved areas of the skin include the abdomen, axilla, paws, ears, and the face. There may be eye discharge and sneezing. Food sensitivity may additionally cause changes in stool or vomiting.

Itching in dogs can be a frustrating problem that affects the quality of life for both the dog and the dog’s family. It is important to note that allergies are not the only reason for itching in dogs. For example, dogs with red, itchy skin can have a skin infection unrelated to an allergy reaction. Since there is no specific test that diagnoses an allergy, it is a diagnosis that is made by excluding other causes. This requires a work up to rule out these other causes. Blood and saliva tests are available to assess if the dog may be reactive to certain allergens. 

Avoidance of the reactive allergen is an obvious way to reduce the allergic inflammation that contributes to the itching, and other allergy associated signs. When avoidance is not possible, antihistamines have been a common approach. This makes sense because histamine plays a part in the allergic inflammation. Antihistamines work by blocking the histamine receptor. Unfortunately, antihistamines do not work well for managing allergic inflammation in dogs. Studies indicate a 0-15% response to antihistamines depending on the particular antihistamine. This may be in part due to antihistamines not controlling the cytokines (a signaling substance) that contribute to inflammation and itching.

Allergies are much more than just histamine. They are complicated problems that can be the result of a dysfunctional immune regulation that allows reaction to allergens or substances that should not normally trigger a reaction. It can be difficult to effectively turn off or reduce the detrimental allergic inflammation and associated processes.

Supportive care involves avoidance of the allergens, controlling associated skin or ear infections, and modulating the allergic inflammatory process. From an integrative perspective, modulating the inflammatory process is complex and involves multiple therapies. Areas of focus for support include the digestive tract which is associated with at least 85% of the immune system, the gut flora that influences the gut function and immune system, the liver that plays a central role in reducing the amount of allergens in the blood derived from the gut and clearing inflammatory compounds, the adrenal glands that are part of reducing inflammation, and reducing stress and anxiety that can trigger increases in the inflammatory process. Management of skin infections that can be secondary to allergies is critical. Drugs like Apoquel and Cytopoint can be a valuable part of reducing the signs associated with allergies. Oral and injectable desensitization products are also available.

Reasonable management goals are to reduce the signs of allergy to a level that is tolerable for the dog and owner. While some dogs have their allergy signs completely disappear, it is more common for some level of allergy sign to be present. If you have questions about allergies, contact your veterinarian.

Ron Carsten, DVM, PhD, CVA, CCRT was one of the first veterinarians in Colorado to use the integrative approach, has lectured widely to veterinarians, and has been a pioneer in the therapeutic use of food concentrates to manage clinical problems. He is also the founder of Colorado Animal Rescue (CARE). In addition to his Doctor of Veterinary Medicine, he holds a PhD in Cell and Molecular Biology and is a Certified Veterinary Acupuncturist and Certified Canine Rehabilitation Therapist. He practices integrative veterinary medicine in Glenwood Springs. Dr. Carsten is the 2022 Colorado Veterinary Medical Association Distinguished Service Award recipient.