Contact Dermatitis in Cats
Dr. Rosanna Marsalla
Contact dermatitis is an uncommon skin disease of dogs and cats caused by contact with plants (especially plants of the wandering Jew family), medications, and various chemicals. Contact dermatitis is not as common in animals as in people because the skin is protected by their hair coat. Contact dermatitis can develop, however, in areas of the body where the hair is sparse. Allergic reactions require a period of sensitization during which the immunologic reaction develops. On the average, sensitization takes six months to two years to develop. Thus, medications and chemicals that have been used in the past without problems still may be responsible for an allergic reaction at some later time.
Contact dermatitis can be of two different types: allergic or irritant.
Contact allergy is a delayed reaction with signs occurring 24 to 48 hours after contact with the offending substance. The reaction is the same type that occurs in people who develop poison ivy.
Typical signs of contact allergy include pruritus (itchiness) and a papular eruption (red bumps). Pruritus can be severe. The paws and muzzle commonly are affected in animals, and sometimes, the insides of the ears are affected. In households with several animals, it is uncommon for more than one animal to develop an allergic reaction.
Irritant reactions, on the other hand, do not require a period of sensitization because they are not immunologically mediated. Thus, reactions occur the first time a substance makes contact with the skin. If several animals are present in the household, all animals coming into contact with the substance will develop skin reactions.
Irritant reactions are more painful than pruritic. Small vesicles (blisters) and ulcerations develop. The distribution of the lesions depends on the nature of the offending substance and the pattern of contact.
Secondary bacterial skin infections may develop due to trauma and inflammation.
What to Watch For
Secondary superficial bacterial infection
Thickening of the skin
Blisters (vesicles) and ulcerations that are more painful than pruritic
The medical history is very important when trying to establish a diagnosis in animals with skin conditions. You will be asked to describe all medications, chemicals, shampoos, and dips that you have used on your cat. Timing also is important when trying to determine the offending substance. It is important to be very thorough when providing information about carpet cleaning, deodorizers, and chemicals applied inside and outside of your house. If the reaction is allergic in nature, products that have been used for a long time cannot be ruled out because of the requirement for a previous sensitization period.
The usual medical approach to an animal with a skin condition proceeds by steps. Thus, your veterinarian will rule out more common diseases before considering a less common disorder such as contact dermatitis. Skin scrapings to rule out demodectic and sarcoptic mange, fungal culture for dermatophytes (ringworm) and antibiotic therapy for possible bacterial skin infection may be necessary.
Diagnosis of contact dermatitis is made by observing resolution of clinical signs after withdrawal of the presumed offending substance and relapse of clinical signs with re-exposure.
Patch testing also may be used to screen suspected chemicals or plants. An area on the lateral chest wall is clipped 24 hours before patch testing.
Samples of various suspected chemicals and plants are applied directly to the skin and bandaged into place to insure prolonged contact with the skin.
After 48 hours, the bandage is removed and the skin examined for reactions. Signs of a positive reaction include erythema (redness), small papules (red bumps) or vesicles (blisters).
The treatment is to remove the cat from the offending substance.
If contact allergy is suspected, you may asked to confine your animal to a limited area of his normal environment to prevent contact with suspected substances. Confinement should start after a thorough bath, because small particles of the substance may remain on the skin and perpetuate clinical signs.
Compliance is very important. If plants are suspected your cat should stay indoors.
Bacterial skin infections occur commonly in cats with contact allergy or irritant reactions. You may be asked to administer an antibiotic for a minimum of three to four weeks.
In severe cases, a course of anti-inflammatory medications such as prednisone may be necessary to make your pet more comfortable. Orally administered medications usually are safer than injectable preparations and should be used as a first choice. Adverse effects of this type of therapy include increased appetite, increased thirst and increased urinations. Avoidance of the offending allergen should be attempted whenever possible, because corticosteroids tend to lose their efficacy with repeated use. This is called tachyphylaxis.