Contact allergies are caused by the aggressive response of specialized immune cells to an allergen. When an allergen activates the immune system, it manufactures a protein that causes the immune cells to release histamine, a naturally occurring compound that has an inflammatory effect on the tissues it comes into contact with. Shampoos for dogs can contain a number of ingredients that can cause skin irritation and even allergic reactions. These reactions usually occur rather rapidly after exposure and often become more intense with repeated applications.

Shampoo allergies are an overactive reaction of the cell of the immune system to a protein within the shampoo that the canine body sees as an intruder.

Contact allergies can sometimes progress to anaphylactic shock. If the following symptoms occur, take your pet to the nearest veterinary office or animal emergency clinic:

Hives, swelling of the face or neck, difficulty breathing, pale gums or collapse.

There are several varieties of shampoo available that can help relieve symptoms related to allergies:

There are several chemicals and other compounds in dog grooming products that can cause contact dermatitis, through either irritation or allergic reaction.

Common allergens 

The general physical exam should reveal allergy symptoms that will most likely prompt your veterinarian to perform further tests. Signs of e.g. red skin and fur loss are not specific to a shampoo allergy so other issues must be ruled out.

The vet may take a skin swab, fur pluck, skin scrape or even a biopsy. The skin samples obtained will then be examined by cutaneous cytology, a microscopic evaluation of the skin cells completed in order to search for problems like mites or yeast infections. 

Allergies to the compounds found in shampoos can manifest anywhere on the body, although true allergic reactions are often centered around the face and groin areas, as well as under the front legs and between the toes. 

The timing of the response combined with the dog’s symptoms may help make a preliminary diagnosis, at which time your veterinarian may recommend a patch test, also known as an intradermal skin test. Miniscule amounts of the suspected antigens are injected under the skin so that a localized reaction can be induced. The antigens introduced in this situation are likely to be ingredients within the shampoo or other grooming products that your dog appears to be reacting to. Many doctors choose to try to diagnose which allergen is causing the reaction by eliminating suspected allergens from the environment first, in this case, changing to an entirely different shampoo.

If you are able to determine the cause of the allergic reaction, you may be able to treat it without a visit to the veterinarian. Any skin that had contact with the shampoo should be completely rinsed in cool water as soon as possible to minimize exposure. Your veterinarian may be able to recommend an appropriate dosage of over-the-counter antihistamine like Benadryl to give your pet to ease the symptoms, or may choose to prescribe topical or oral antihistamines or corticosteroids. Caution should be employed during application of hydrocortisone creams, as ingestion could cause gastric distress. 

Medications such as corticosteroid injections or oral tablets are usually very efficient in reducing the signs and symptoms of allergy, but they are only recommended when other treatments have failed as they have some serious side effects. If your pet is showing signs of anaphylactic shock, treatment will need to begin before a definitive diagnosis is received. Epinephrine will be administered upon your arrival to the veterinarian’s office and supportive therapies such as IV fluids and oxygen are likely to be started at that time as well.

Canine contact allergies can be just as unsightly and uncomfortable for our canine companions as they are for us and continuing treatment can be more than just cosmetic. Skin that has been damaged by allergic reactions is prone to developing bacterial infections, and either oral or topical antibiotics will be prescribed if this occurs. It is essential that your pet completes the full course of their antibiotic medication even if the symptoms seem to have subsided. Stopping the medication before the infection is completely eradicated may cause the infection to reoccur. Quite often a simple switch in the choice of shampoos is enough to ease the allergic response. Allergenic ingredients should be avoided for the rest of the patient's life.