Allergic contact dermatitis occurs in dogs as a hypersensitivity reaction to certain molecules in the pet's environment. Irritant contact dermatitis results when the skin is exposed to noxious substances in the environment. The symptoms and biologic mechanisms involved in these two diseases are similar so they are often discussed together.
What is allergic contact dermatitis?
Allergic contact dermatitis is a rare disease, which occurs when an animal's skin overreacts to certain small molecules in the environment. Substances, which can cause allergic contact dermatitis include certain antibiotics applied to the skin; metals such as nickel; materials such as rubber or wool; and chemicals such as dyes and carpet deodorizers.
What is irritant contact dermatitis?
Irritant contact dermatitis occurs when the skin is exposed to severely irritating chemicals such as the sap in poison ivy and salt on the road.
How do these two diseases differ?
Allergic contact dermatitis only affects those animals with a hypersensitivity to the molecule. Irritant contact dermatitis would affect every dog that is exposed to the irritant.
Allergic dermatitis requires multiple exposures to the molecule before it develops. It rarely occurs in animals less than two years old. Irritant contact dermatitis often occurs in inquisitive young animals who get into things they should not.
What are the symptoms of allergic and irritant contact dermatitis?
Lesions generally occur on the areas of skin that are sparsely haired and directly exposed to the offending molecules. This often means the back of the paws, abdomen, muzzle, and lips. The affected areas are very red, have small bumps or vesicles (blister-like lesions), and itch. In irritant contact dermatitis ulcers may appear.
How are allergic and irritant contact dermatitis diagnosed?
The history and physical exam can often indicate what is going on. To isolate the allergen (molecule that caused the dermatitis), exclusion trials are often performed. In these trials, the animal is restricted to an uncarpeted room and kept off the grass, for instance. If the animal's condition improves, potential allergens are slowly introduced one by one.
A 'patch' test can also be performed. In this test, a small amount of the allergen is rubbed on the skin, or a gauze pad containing the suspected allergen is bandaged on the pet's skin. The skin is monitored for 2-5 days for a reaction.
How are pets with allergic or irritant contact dermatitis managed?
The key to managing this condition is removing or restricting exposure to the allergen or contact irritant in the pet's environment. If that is not possible, then fatty acids, antihistamines, biotin, and topical shampoos can be used to control the itching.
As a rule, for any pet suspected of having an allergy problem that could include an allergic contact component, we recommend:
- Glass or stainless steel food and water bowls, cleaned and rinsed well daily
- Hypoallergenic detergents for the pet's bedding
- Routine hypoallergenic shampoos for the pet to remove any allergens
- Restricting walking to sidewalks or paved surfaces - avoid grass