Allergic Contact Dermatitis is an inflammatory skin condition that occurs when your pet comes into direct contact with a substance that they are allergic to. As this is an allergic response, usually the substance that the pet is allergic to is otherwise harmless in normal pets. In contrast, Irritant Contact Dermatitis is an inflammatory reaction to a substance which is known to be an irritant. As our focus is more about hypersensitivities, Allergic Contact Dermatitis is what will be discussed in this section.
The most common allergens are plants such as “Wandering Jew” and “Moses in the Cradle”, however other substances such as cement, floor polishes and carpet deodorisers have been shown to affect pets as well. Because this type of allergy requires direct contact between the skin the offending substance, usually only sparsely haired areas, which are in contact with the ground, are affected. When very hairy areas are affected with dermatitis, we are less suspicious of contact dermatitis.
Common symptoms include red, inflamed bumps (macules and papules) which can be very itchy. The affected areas can include the abdomen and underside of the chest, underneath the tail, front of the neck and chin and the inside of the ear pinnae (ear flaps). Over time, these lesions may spread to involve larger areas as hair loss progresses in nearby areas. Depending on the offending substance, clinical signs may be seasonal or non-seasonal.
A diagnosis of contact dermatitis is made by combining information from the pet’s history with observation of the location of the skin lesions and demonstrating that the clinical signs resolve when the pet is isolated from possible allergens. To maximise the effect of the isolation trial, we usually recommend that the pet is first bathed with a gentle, hypoallergenic shampoo to remove possible allergens. A “patch test” can also be performed which involves applying the suspected allergens to the skin and seeing if a localised reaction occurs. This can help determine which plants or materials are likely to be the cause of the contact dermatitis.
Once diagnosed, management of these cases relies on avoidance of the allergens. However, this may not be possible in every case and topical anti-inflammatory medications can be useful in the management of patients with contact dermatitis. In more severe cases systemic anti-inflammatory and anti-itch medications may be required.