Contact Dermatitis in Dogs

Summary

Contact dermatitis refers to inflammation of the skin in response to an allergen or irritant making physical contact with a dog’s skin cells. There are two types of contact dermatitis: allergic and irritant. 

Chemicals, objects, medications, or plants that directly damage skin cells cause irritant contact dermatitis. Examples of irritants include cedar chips, detergents, deodorizers, soaps, herbicides, or topical medications. These irritants generally affect every pet in the household similarly. 

Allergic contact dermatitis occurs when the immune system activates against a specific allergen. The most common contact allergen in dogs is flea saliva, which causes a specific subtype of dermatitis called flea allergy dermatitis. Other allergens reported in dogs include pollen, dander, dust mites, and mold spores. 

Both types of contact dermatitis have similar symptoms, with dogs showing reddened, swollen, or crusty skin that is often extremely itchy. Some dogs develop raised, blister-like bumps on their skin or weeping, open sores. Dogs with symptoms of contact dermatitis require prompt veterinary attention, but it is not a life-threatening emergency.  Once other causes of skin inflammation are ruled out, diagnosis of contact dermatitis typically involves removing suspected allergens or irritants from the dog’s presence to see if symptoms resolve. If symptoms return when the substance is reintroduced, then a diagnosis is confirmed. If there are many suspected triggers, a patch test is used to test multiple substances at the same time. 

Contact dermatitis is treated by avoiding contact with the known trigger. Bathing is helpful for removing both irritants and allergies from the dog’s skin. If complete avoidance of the inflammatory trigger is impossible, using shirts or socks to provide a physical barrier between the dog’s skin and the irritant or allergen is helpful.

Risk Factors

Contact dermatitis is uncommon in dogs, with the exception of Flea Allergy Dermatitis (FAD), which is the most common allergy in dogs.

Although it is a life-long condition, contact dermatitis has a good prognosis with appropriate management. Contact dermatitis is often severely itchy, but is not a life-threatening emergency.

Possible Causes

Both allergens and irritants cause contact dermatitis. Irritants are chemicals, objects, medications, or plants that cause direct damage to the skin. Irritants generally affect every pet in the household. Examples include, but are not limited to:

• Cedar chips • Textiles • Plastics • Metal • Fertilizers • Cleaning chemicals • Carpet or litter deodorizers

• Soaps and shampoos • Insecticides • Herbicides • Topical medications

Unlike irritants, allergens activate the immune system to produce skin inflammation. Allergies develop over time, following multiple exposures.

Fleas are the most common cause of contact allergies in dogs. This subtype of contact dermatitis is called flea allergy dermatitis. Other less-common contact allergens include:

• Pollens • Dust mites • Mold spores • Animal or human dander • Insects • Environmental yeasts

Main Symptoms

Contact dermatitis primarily occurs on the parts of a dog’s body that have less hair, as these areas have less protection to prevent the allergen or irritant from accessing the skin. Symptoms include:

• Reddening, swelling, or crusting of the skin • Darkening of the skin • Raised bumps on the skin

Detailed Characterization

In some cases, contact allergies are extremely itchy and owners may notice hair loss in the itchy area. 

Untreated contact allergies often become infected and painful, leading to skin lesions commonly referred to as hot spots. Hot spots, in turn, can become infected.

Symptoms of skin infections include:

• Weeping, open sores • Pus or blood oozing from the skin • Bad odor emanating from the sore

Testing and Diagnosis

Identifying the cause of contact dermatitis often requires multiple steps. A review of the dog’s activities, lifestyle, and other factors help to identify potential triggers of the skin reaction.

As with other types of allergies, multiple diagnostics are usually performed to rule out other causes of the inflammation. These tests include:

• Skin scraping  • Fungal culture • Skin or ear swab 

Contact dermatitis is suspected when other causes of skin inflammation are ruled out. The diagnosis is confirmed with a withdrawal test. The suspected irritant or allergen is removed from the dog’s presence. If symptoms resolve, and return upon re-exposure to that irritant or allergen, then the diagnosis is confirmed. 

If there are many suspected allergens or irritants based on the dog’s history, the veterinarian uses patch tests to trial several possible items. In this test, the hair on an area of the body is clipped, and samples of suspected irritants or allergens are applied to the skin and bandaged in place. Samples that produce symptoms are confirmed as contact dermatitis-causing agents in that dog.

Steps to Recovery

Contact dermatitis is a life-long condition, but symptoms are expected to resolve as long as the irritant or allergen is removed. Treatment for contact dermatitis primarily involves eliminating the allergen or irritant through environmental changes. Bathing the dog routinely helps remove allergens and irritants from the skin. If removing the allergen or irritant is impossible, using a physical barrier such as socks or a shirt to separate the dog from the allergen or irritant helps reduce symptoms. Anti Inflammatory medications may be recommended when symptoms are present. Secondary skin infections are treated with antimicrobial medications as required.

Prevention

As with any type of allergic reaction, the cause is unknown. Genetic predisposition may play a factor.  Once contact dermatitis is diagnosed, recurring symptoms are prevented by removing the trigger from having contact with the dog.

Is Contact Dermatitis Common in Dogs?

Contact dermatitis is uncommon in dogs. Allergic contact dermatitis is more common in dog breeds with an existing predisposition to allergies.

Typical Treatment

Contact dermatitis is generally treated by 

• Preventing/limiting exposure to the trigger • Soothing shampoos • Treatment of secondary infections

• Anti-inflammatories