Pruritus, or itching, in dogs and cats, can involve scratching and licking, chewing, or biting the skin. Pruritus is the most common symptom of skin disease in veterinary medicine. Many conditions can cause pruritus, including allergies, fleas, and other skin parasites. Some skin problems are more common in younger animals, while others are diagnosed more often in older pets. 

Medications are available to manage pruritus, but unless the underlying cause of the pruritus is diagnosed and addressed, it will return once the medication is stopped. Some anti-pruritic medications, such as steroids, can result in other health issues. Providing your dog or cat's medical history can sometimes help your veterinarian determine the cause of the itching. 

A lack of response to some medications can help your pet’s veterinarian narrow down the possible causes. Additionally, some medications can actually cause itching.

When Did the Pruritus Start?

It can be helpful to know when the itching started. If allergies cause itching, it is beneficial to know if the problem is worse at different times of the year.  

Other Health Problems 
Sometimes, skin conditions develop secondary to another health problem. Your veterinarian will ask questions about other symptoms that could point to a specific cause of pruritus. For example, pets with food allergies may have frequent bowel movements or soft stools.

Location of Skin Lesions
Some pruritic skin conditions cause skin lesions more commonly in one body region than another.

Type of Skin Lesions
Although most pruritic skin conditions look the same to pet owners, there are actually many types of skin lesions, and some skin lesions occur more commonly with specific skin conditions. However, if the pruritus has become chronic, many pruritic skin conditions look similar to each other. Your veterinarian may need to run some tests to help determine the cause of the pruritus.

What Tests are Used to Diagnose the Cause of Pruritus?

Below is a list of some common tests for diagnosing the cause. Your veterinarian will select tests based on your pet’s medical history and examination findings. 

Skin Scrapings
To look for skin parasites, a scalpel blade is used to gently scrape the skin layers to collect cells and any skin mites. The sample is then examined under the microscope.

Skin Cytology
To look for bacteria and yeast organisms, skin cells and debris samples are collected and placed on a glass slide for examination under the microscope. This test can also help determine what types of cells are in the skin.

Parasite Therapy Trial
For some parasites, the only way to determine if they are the cause of the itching is to treat the parasites. A decrease in pruritus after the anti-parasite therapy would be consistent with the parasite causing the pruritus.

Ringworm Testing
To determine if a dog or cat’s skin is infected with ringworm (a disease caused by a fungus called a dermatophyte, not actually a worm), your veterinarian may start by examining your pet under a special ultraviolet lamp called a Wood’s Lamp. If the hairs glow (fluoresce), this may mean your pet has ringworm  Those hairs are collected for further testing. In a fungal culture, hair and skin samples are placed on a fungal culture plate. If a dermatophyte grows, the dog or cat is diagnosed with ringworm. In a dermatophyte PCR test, (a test that looks for viral diseases) the hair and skin samples are checked for dermatophyte DNA. 

Food Trial
A prescription or home-cooked diet is fed for several weeks with no other foods or treats to diagnose food allergies. Unfortunately, there is no reliable skin or blood test in dogs and cats to diagnose food allergies.

Allergy Testing
Skin or blood allergy testing is used in dogs and cats that have had other causes of pruritus ruled out through other tests. It is mainly used to select allergens for a type of allergy treatment called allergen-specific immunotherapy. There are no reliable hair or salivary tests to diagnose allergies.

Skin Biopsy
A sample of skin can be obtained through minor skin surgery. Skin biopsy is especially helpful for diagnosing some less common causes of pruritus, such as skin cancer. However, a skin biopsy cannot be used as an allergy test and cannot diagnose the cause of a pet’s allergies.