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What the Heck is That on My Cat?

Updated: October 13, 2020
Published: April 28, 2016
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What the Heck is That on My Cat?

Skin lesions on cats have many causes including parasites, allergies, medication reactions, and cancer. Wouldn’t it be handy if you could just look at your cat and know what the problem is? Unfortunately, this isn’t often the case. The skin has only a limited number of ways to react to whatever is bothering it, but sometimes there are clues as to what is going on.  


A flea infestation may be identified by closely examining your cat’s skin and fur. If you are lucky, you may find fleas or flea dirt (black debris that is made up of dried, digested blood), but a pattern of hair loss, itching, and scabs focused around the lower back, base of the tail, and the ears should arouse suspicion as well. Treating all the animals in your house with an effective flea medication (monthly topical and oral products work well) may be all that is needed for your cat’s skin to heal.


Mite infestations occur when a normal skin inhabitant is allowed to over-reproduce or more commonly when a contagious mite is acquired. Skin lesions range from hair loss and redness to papules, scales, and crusts. Many areas of the body can be affected. Your veterinarian will need to perform skin tests to identify the offending parasite and prescribe an appropriate medication.


Healthy skin has excellent, natural defenses against bacterial and yeast infections, but when a cat has an underlying problem that disrupts the surface of the skin, bacteria and yeast can take advantage of the situation. Your veterinarian can diagnose the secondary infection as well as address the underlying cause. 


Allergies are the result of overactive immune reactions that produce a variety of skin lesions including itching, redness, hair loss, or a scabby, generalized rash known as “miliary dermatitis.” If a food allergy is suspected, a veterinarian-prescribed food trial during which the cat eats only a hypoallergenic food will be necessary to reach a diagnosis. If an environmental allergy is more likely, you may choose to identify the offending allergens with blood or skin testing and then treat your cat with desensitizing shots or an oral serum, or begin symptomatic treatment with medications that suppress your cat’s immune system. Life-long treatment may be necessary to provide comfort to an allergic cat.

Eosinophilic Granuloma Complex

Eosinophilic granuloma complex is another indicator of allergies in cats. The allergic response may be caused by a hypersensitivity reaction to parasites, food, or environmental triggers. Diagnosis is often made based on the presence of characteristic lip ulcers or red, raised plaques on the skin but may require cytology (examination of cells) or biopsy of the tissue. Treatment with an immunosuppressant may calm the lesions, but correcting the underlying cause will help prevent recurrences.


Ringworm (dermatophytosis) is a contagious infection caused by a fungus. The lesions it causes are variable and range from redness and hair loss to scabs and crusts. Diagnosis involves growing the fungus on a special culture medium and may take several weeks to complete. Treatment can include weekly dips, medicated shampoos or prescription medications. Decontamination of the environment as recommended by your veterinarian helps to reduce the chances that the infection will spread to other pets and people.

Medication Reactions

Drug reactions may occur when starting any new medication or after receiving the medication for a long period of time. Symptoms range from mild itchiness to rashes, blisters, sloughing of skin, and systemic illness. If the medication is stopped (under veterinary supervision) and the signs resolve, a drug reaction is the likely diagnosis. Avoidance of the medication in the future is recommended as future reactions are often much worse.

Skin Tumors/Cancer

Most skin tumors in cats form discrete masses in the skin. However, one type of skin cancer, cutaneous lymphoma, mimics other skin diseases by producing symptoms like hair loss, redness, itching and scaly skin. Cats with skin cancer are usually, but not always, older individuals. Biopsy is required to identify the type of cancer and plan what type of treatment (surgery, chemotherapy, radiation treatment, or palliative care) would be in the cat’s best interests. 

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