Contact Allergies

I have been told that my dog has a contact allergy. What is this?

Contact Allergy (Contact Dermatitis) is a type of allergy that requires direct contact between the skin and the substance in question. Many substances can induce contact allergy. These include certain plant materials, e.g. “Wandering dew” (Tradescantia spp.), “Moses in the Cradle” (Rhoeo spp.) and other succulent ground cover plants, pine oil (or even pine needles), floor polishes, disinfectants, wool, nylon and dyes. Sometimes shampoos, ointments and insecticides used in the treatment of skin disease can be implicated.

"Because dogs are covered with hair, contact allergy is a rare disorder compared with people where it is relatively common."

My dog keeps licking himself underneath, particularly around his private parts which are inflamed and sore. Is this likely to be due to his contact allergy?

Symptoms usually involve intense pruritus (itching) on contact sites such as the feet, skin, scrotum, elbows and hocks. Because the substance must touch the skin we usually suspect contact allergy only when the hairless/lightly haired regions are affected.

Diagnosis

Diagnosis is sometimes obvious but may require avoidance trials or patch testing. Patch testing involves placing suspected allergens on the skin and leaving them for up to 72hrs and assessing the immune response to the plant or chemical.

Does the condition develop rapidly?

This depends on the cause allergen. Usually contact hypersensitivity develops relatively slowly. Please see below, irritant dermatitis.

Is there any difference between contact allergic dermatitis and contact irritant dermatitis?

Yes. Contact irritant dermatitis is not uncommon in dogs and should be distinguished from a contact allergy. Only a small percentage of dogs will have an allergic response to a contact allergen whereas all dogs will have a skin reaction on exposure to an irritant.

Common irritants include creosote, concentrated disinfectant or detergent solutions.

Clinical signs of contact irritation are similar to contact allergy but occur very rapidly.

Treatment & Prevention of contact dermatitis

Medical treatment of contact allergy once it arises usually involves cortisone. Apoquel (oclacitinib) is also now available. Long term prevention requires avoidance of physical contact with the offending substance. This may involve removing the offending plant if possible and sometimes involves the use of a lycra bodysuit. If avoidance is impossible then anti-inflammatory creams, lotions or sprays may be part of the treatment to reduce the inflammation.