Dermatitis due to allergy is rare in young animals, and is extremely rare in cats unless they are exposed to insecticides that contain oil extracted from a citrus rind, a common allergen. Contact dermatitis may be caused by an allergy, or it may simply mean that your cat has touched something that has irritated its skin, such as the sap in poison ivy, or salt on a road. It is usually limited to one area; an overall reaction, as from shampoo, is uncommon. It can be difficult to distinguish one cause from another because the symptoms usually appear the same. If it seems to occur at certain seasons, it may indicate that the offending source is a plant or outdoor compound.
Allergic reactions require a previous, sensitizing experience with the irritant. The next contact with the irritant is when symptoms tend to occur. Some animals can have reactive dermatitis from medications. Allergies can occur at any age, and are a direct result of the irritating nature of the offending compound and the body's particular reaction to it.
Symptoms and Types
Cats suffering from contact dermatitis will most likely be afflicted with rashes and/or bumps where the skin has come into contact with the ground (i.e., the chin, neck, chest, abdomen, groin, anal area, scrotum, tail, and between the toes). These rashes may stop abruptly at the hairline. Other common symptoms include severe itching and swelling.
Factors and/or substances that have been reported to be skin irritants are:
- Mulch/Cedar chips
- Rough surfaces
- Floor waxes/cleaning products – especially those containing citrus oil
- Carpet and litter deodorizers
- Sensitivity to the sun/heat
- Topical agents
- Food allergy
- Insect bites (bees, wasps)
- Bacterial infection
- Fungal infection (e.g., ringworm)
- Flea collars
- Parasitic hypersensitivity or infestation (e.g., mites, fleas)
- Insecticides, including newer topical flea treatments; those including citrus rind are more likely to cause reactions in cats
You will need to give a thorough history of your pet's health, onset of symptoms, and possible incidents that might have precipitated this condition. To avoid aggravating the condition, the symptoms cannot be treated until tests have been completed. Your veterinarian's first task will be to find out what the offending irritant, or trigger, is. There are several ways to approach tracking down the triggers. One is to do what is called a patch test: the suspected substance is placed on a patch and taped to the skin for 48 hours. Any reaction is then assessed. The second method is to remove the pet from the offending environment for a period of time and then return it to the environment, monitoring what happens and whether it has had any impact one way or the other. An allergy diary, where you keep a record of your cat's immediate environment, daily diet, and known activities can help you to narrow the possible causes for your cat's symptoms.
Your veterinarian will also want to perform bacterial cultures. A clip of hair may be taken from a patch of skin in an area that is not affected, applied to a sample of the suspected antigen, and observed for possible reaction. Skin biopsies may also be required for making a definitive diagnosis.