Causes of Skin Ulcers & Draining, Oozing, or Crusty Lesions on Cats

Draining and crusty abscess on the head of a cat

The first sign of a skin problem may be a crusty area on the skin, nose, or foot. In other cases, skin problems which may start out small can progress and develop into more extensive lesions. They may open, drain, and then develop a crusty surface. In some instances there may be hair loss, and the surface of the skin can become red and oozing, and ulcers may develop. Most of the conditions which can cause these lesions are included in the table below. This extensive listing helps you understand why a quick diagnosis may be difficult to make and various diagnostic tests may need to be performed. The most common conditions causing these lesions are color-coded gray in the table (some may be more common in certain geographical areas).

Condition	Description	Symptoms	Diagnosis	Treatment
Abscesses	Accumulation of pus; may or may not be caused by an infection; in cats, often due to bite wounds	These may appear as firm, fluid-filled nodules of varying shapes and sizes, with small crusty area at puncture site; if due to infection, cat may have fever, loss of appetite, depression; may open and drain	History, physical exam, needle aspirate	Surgically open, drain, and flush; if infected, administer appropriate antibiotics
Aspergillosis	Fungal infection which usually enters through the nose	Ulcerated, draining lesion on nose; also see drainage from nostrils and pain	Microscopic examination of drainage; biopsy; blood tests	Antifungal medications
Bacterial infection (pyoderma) *See Folliculitis, Pyoderma-deep*	Often occurs as a result of another condition such as a parasite, allergic, or hormonal conditon
Basal cell tumors	Most common skin tumor in cats; benign tumors; may become cancerous, slow-growing tumors which rarely metastasize	Single, sometimes fluid-filled nodules which may ulcerate; usually on the head, neck, and chest; may be hyperpigmented	Biopsy	Surgical removal (if benign, surgical removal is optional)
Bee, wasp, hornet stings	Skin reactions can vary dramatically in severity	Immediately after the bite, see swelling, redness, pain, possibly itching; subsequently may develop extensive ulcers with draining; may develop hives or anaphylaxis	History, physical exam	Antihistamines, steroids; wet dressings if ulcerated; protect the area from self-inflicted trauma
Bite wounds *See Abscesses*
Bowen's disease	A rare type of squamous cell carcinoma in which multiple lesions develop	Lesions start out as thickened, dark, raised and well-delineated; progress to ulcers and crusts and bleed easily; found on the head, neck, shoulders, and forelegs	Biopsy	Lesions may come and go and are not always treated; some anti-cancer drugs and radiation have been tried with mixed results
Burns	Appearance and treatment depend upon severity of burn	Lesions may not appear until 24-48 hours after the exposure; skin hard and dry; blisters rarely seen; if severe (full thickness of the skin is affected) see necrosis and sloughing of skin 7-14 days after the burn occurs	History, physical examination	Immediately cool affected area if burn occurred in the last 2 hours; further treatment depends on severity; keep area clean; prevent secondary infections, topical silver sulfadiazine is useful; treat other symptoms which may occur: dehydration, shock, etc.; pain management; no steroids
Coccidioidomycosis	Caused by the fungus Coccidioides immitis found in the soil in the Southwestern U.S.	Draining nodules, fever, weight loss; unlike dogs, no respiratory signs	Microscopic examination of drainage; blood test	Ketoconazole, itraconazole
Cold agglutinin disease	Rare disease in which proteins in the blood coagulate in cold temperature and block small blood vessels causing skin damage; may be a result of lead poisoning or autoimmune disease	Redness, ulcers, possibly necrosis; lesions usually on ears, tail, and extremities	History of exposure to cold; special blood tests including the Coomb's test; biopsy	Treat any underlying cause; avoid cold; steroids and immunosuppressants
Cryptococcosis	Fungal infection often transmitted through bird droppings; more common in cats with suppressed immune systems	Nodules often over the nose which may ulcerate; many other signs depending on what other body systems are infected	Microscopic exam of discharge, blood tests, culture, biopsy; look for underlying cause of immunosuppression	Itraconazole
Drug or injection reaction	Rare skin reaction to a drug which is inhaled, given orally, or applied topically; more common with penicillins, sulfonamides, and cephalosporins; usually occurs within 2 weeks of giving the drug	Can vary widely and may include itching, hair loss, redness, swelling, papules, crusts, ulcers, and draining wounds	History of being treated with a drug, symptoms, biopsy	Discontinue offending drug; treat symptomatically
Eosinophilic granuloma	Part of the common eosinophilic allergic syndrome in cats which includes eosinophilic plaques, miliary dermatitis, and rodent ulcers	Elongated, raised, oozing, and possibly ulcerated lesions, with hair loss; may be single or multiple; often on back of thighs	Microscopic examination of swab from lesion, biopsy, CBC (find increased eosinophils); look for underlying cause, e.g., parasites, food allergy, atopy	Treat underlying cause if found; corticosteroids; fatty acid supplements; immunosuppressive drugs in severe cases
Eosinophilic plaques	Part of the common eosinophilic allergic syndrome in cats; see also eosinophilic granulomas, miliary dermatitis, and rodent ulcer	Intense itching; raised, oval, oozing, and possibly ulcerated lesions; may be single or multiple; often on abdomen and thighs	Microscopic examination of swab from lesion, biopsy, CBC (find increased eosinophils); look for underlying cause, e.g., parasites, food allergy, atopy	Treat underlying cause if found; corticosteroids; fatty acid supplements; immunosuppressive drugs in severe cases
Epitheliotropic lymphoma (mycosis fungoides)	Rare cancer of T lymphocytes seen in older cats; may be associated with FeLV	Redness, itching, scales, ulcerated nodules	Needle or other biopsy	Poor response to treatments which include chemotherapy, surgical removal, retinoids, fatty acids
Erythema multiforme	Hypersensitivity reaction to infections or drugs; may also be caused by cancer or other diseases	Hair loss, 'bull's eye' lesions, and vesicles often around mouth, ears, groin and axilla; in some instances, ulcers develop; depression, fever	History, clinical signs, rule out other diseases causing similar signs; skin biopsy	Treat or remove underlying cause
Feline herpesvirus and calicivirus	Commonly see respiratory signs; skin lesions may occur in cats who are stressed or immunosuppressed	May see ulcers on feet and head; upper respiratory signs and oral ulcers usually present	Virus isolation, biopsy; check for underlying disease or stress	Good nutrition, antibiotics, antiviral medications, NO steroids
Feline leprosy	Caused by the bacteria 'Mycobacterium'; usually seen in young cats	Single or multiple nodules which may drain; usually on head or neck; nonpainful; cat does not show other signs of disease	Biopsy, culture	Surgical removal, anti-mycobacterial drugs such as rifampin or clofazimine
Feline pox	Viral disease; outdoor cats more commonly affected; presumably transmitted by bite wounds	Nodule at the site of a previous bite wound; progresses to multiple nodules which may ulcerate and have crusts; may itch	History, physical exam; biopsy; specialized testing to identify the virus	Lesions usually resolve in 3-4 weeks; anitbiotics for any secondary infection; antihistamines for itching; no steroids; in some cats, lesions progress and do not respond to treatment
Fibrosarcoma	Rapidly growing, invasive tumor; may occur at the site of a vaccination or injection, especially in cats; may be induced by a form of FeLV	Irregular-shaped, firm nodule; may ulcerate	Biopsy	Surgical removal, however, since tumor is invasive need to remove large area around tumor, sometimes including large masses of muscle and bone; if tumor is on a leg, amputation of the leg is commonly recommended; surgery may be combined with chemotherapy and radiation
Flea allergy dermatitis (flea bite hypersensitivity)	Severe reaction by the cat to the saliva of the flea	Intense itching, redness, hair loss papules, crusts, and scales; sometimes development of infection or hot spots	Presence of fleas; reaction to intradermal testing	Flea Control in the environment and on the cat; steroids and antihistamines for the itching
Folliculitis	Infection of the hair follicles; symptoms usually appear on face, neck, and head	Pustules develop in the hair follicles and open and form crusts; may itch and develop hair loss	Skin scraping; culture; biopsy; look for underlying condition such as allergy or FIV	Antibiotics, usually for 3-4 weeks; treat any underlying condition
Frostbite	Appearance and treatment depend upon severity of exposure	Ears, tail tip, and feet most often affected; when frozen skin is pale and cold; upon thawing, areas are red and painful; if severe, the skin may be sloughed (1-2 weeks later)	History, clinical signs	Rapidly thaw affected areas with warm water; surgical intervention if severe. Avoid thawing and refreezing since this results in extensive skin damage.
Granulomas	May be due to infections; the body's reaction to foreign material such as plant material (e.g., foxtail) and suture material; other constant irritation; or unknown causes	Solid firm nodules of varying sizes; those due to foreign bodies often have draining tracts; may develop hair loss, ulcers, and secondary infections	History, clinical signs, biopsy, surgical exploratory	Surgical removal of the foreign body (in the case of plant material, tracts may be extensive and require major surgery); antibiotics if infected; treat any other underlying cause
Hemangiosarcoma	Malignant, invasive tumor more common on sun-damaged skin	Blue to reddish black nodule; usually on ears, head, legs, groin, and axillae; often ulcerate	Biopsy	Surgical removal; need to remove large area around the tumor; if tumor is on a leg, amputation of the leg is commonly recommended
Histoplasmosis	Fungal infection which can rarely cause skin lesions	Ulcerated and draining nodules; most commonly see respiratory and gastrointestinal symptoms	Needle aspirate or biopsy	Ketoconazole, itraconazole
Hot spots (acute moist dermatitis)	Result from allergies, flea bites, mange, anal gland disease, poor grooming, ear infections, plant awns or burs, arthritis	Hair loss; red, moist, oozing skin; constant licking or scratching	Physical exam and history	Treat underlying condition; clean area; apply Domeboro solution; topical and/or oral antibiotics and steroids
Hyperthyroidism	Approximately 1/3 of cats with this disease will have skin lesions; caused by excess secretion of thyroid hormone	Hair loss; hair easily pulled out; seborrhea; cats may overgroom and cause 'hot spots'	Physical exam; blood testing for thyroid hormones	Remove part of thyroid; radioactive iodine therapy; methimazole
Lice	Infection with several species of lice	Variable: itching, hair loss, crusts, rough hair coat	Finding lice or nits on skin or hair	Pyrethrin, ivermectin (off-label use*)
Lupus erythematosus	Autoimmune disease affecting many body systems inlcuding joints, kidneys, muscles, nervous system	Skin lesions may include thickening or ulcers of the foot pads, scaling, and recurring bacterial infections with pustules	Special blood tests (LE test); biopsy	Prednisone and other immunosuppressive drugs; treat underlying infections
Lymphoma	Type of cancer; may occur in other organs without skin involvement	Nodules with ulcers; redness	Biopsy	Surgery, chemotherapy, radiation; lymphoma of the skin does not usually respond to treatment as well as other lymphomas
Mammary cancer	Most common in unspayed females; in cats, 85% are malignant	Single or multiple nodules under the skin, of varying sizes, often irregular in shape; may ulcerate and drain	Biopsy	Surgical removal
Mast cell tumor	Common cancer which is graded from 1-4: Grade 1 is one slow-growing tumor, and Grade 4 is rapidly growing malignant tumors with metastasis; in cats most are Grade 1	Tumors may be of various sizes, appearances, and numbers	Biopsy to grade the tumors which determines treatment and prognosis	Depends upon grade; surgical removal, taking large area around tumor; chemotherapy; prednisone; radiation
Melanoma	Malignant tumor; uncommon in cats	Usually single, dark-colored nodule which often ulcerates	Biopsy	Surgical removal, taking large area around tumor
Miliary dermatitis in cats	Part of the common eosinophilic allergic syndrome in cats which includes eosinophilic granulomas, eosinophilic plaques, and rodent ulcers; may also be associated with infections, autoimmune diseases, hormonal disorders, and nutritional deficiencies	Multiple small crusty bumps, usually over hips, neck, and back of thighs; moderate to severe itching	Microscopic examination of swab from lesion, biopsy, CBC (find increased eosinophils); look for underlying cause, e.g., parasites, food allergy, atopy	Treat underlying cause if found; corticosteroids; fatty acid supplements
Mosquito bite hypersensitivity	Severe allergic reaction to mosquito bites; lesions most common on nose and ear tips - also footpads, lips, and chin	Acute lesions are red, raised, and oozing; with time develop hair loss, scales, nodules and pigment changes; some cats develop fever and swollen lymph nodes	History of exposure to mosquitoes; lesions resolve when cat is hospitalized or otherwise restricted from exposure to mosquitoes	Restrict exposure to mosquitoes, insect repellents, prednisone
Nocardia	Bacterial infection usually acquired from a puncture wound	Usually see respiratory signs; skin lesions include draining nodules	Bacterial culture, microscopic examination of drainage	Poor prognosis; antibiotics
Notoedric mange	Infection with the Notoedres mite	Intense itching and self-trauma, skin thickening, gray crusts develop	Skin scraping and microscopic examination	Lime sulfur dips, ivermectin (off-label use*)
Panniculitis	May be caused by trauma, foreign bodies, infections, autoimmune diseases, or unknown causes	Deep-seated nodules, often ulcerated and draining; usually on the body vs. the head or limbs; may see loss of appetite, depression	Microscopic exam of drainage; biopsy; tests to rule out other causes	Surgical removal; if multiple lesions, prednisone and Vitamin E; may need long-term treatment
Pemphigus erythematosus	Less severe form of pemphigus foliaceus, an autoimmune disease; exposure to sunlight may play a role in its development	Pustules, drainage and crusts; usually on face and ears	History, physical exam, skin scraping and biopsy	Topical and oral steriods; other immunosuppressives
Pemphigus foliaceus	The most common form of pemphigus in the cat; an autoimmune disease	Often affects feet and head; starts with pustules and progresses to severe crusting; depigmentation of the nose is common; itching may occur; if footpads and nails affected often see lameness; symptoms wax and wane; severely affected cats may have fever and loss of appetite	History, physical exam, skin scraping and biopsy	Corticosteroids, other immunosuppressive therapy, gold injections
Pemphigus vulgaris	A rare form of pemphigus, an autoimmune disease	Large vesicles which break open, ulcerate and develop thick crusts; lesions often found in the mouth	Biopsy	Poor prognosis; prednisolone and other immunosuppressants
Phaeohyphomycosis	Caused by wound contamination with a fungus	A single nodule on the legs or multiple ulcerated and draining nodules over the body	Microscopic examination of drainage, culture, biopsy	Surgical removal though often recur; possible antifungal medications
Psychogenic (neurogenic) dermatitis	Self-licking in cats results in self-trauma; possible causes include anxiety, boredom, stress (e.g., new member in household)	Symmetrical hair loss, sometimes ulcers, on abdomen, groin, along the back	Exclude other causes; history important	Relieve underlying cause e.g., anxiety; restrict licking; behavior modifying medication may be necessary
Pyoderma-deep	Bacterial infections of skin and underlying tissue often secondary to another skin disease such as self-inflicted trauma, wounds, acral lick granulomas, allergies, seborrhea	Ulcerated pustules or nodules, draining tracts, crusts, thickened skin	Skin scrapings, biopsy, culture	Clip and cleanse area; antibiotics, prevent self-trauma (licking, scratching), NO steroids
Pyoderma-superficial *See Folliculitis*
Pythiosis	Caused by an aquatic mold	Ulcerated draining nodules on the legs, head, and base of tail which, may itch; often see other signs of illness due to infection of the gastrointestinal tract	Microscopic examination of drainage; biopsy	Often fatal; surgical removal
Ringworm	Infection with several types of fungus	Hair loss, scaliness, crusty areas, some itching	Culture	Miconazole, lime sulfur dips; oral griseofulvin or itraconazole; ringworm vaccine
Rodent (indolent) ulcer	Part of the common eosinophilic allergic syndrome in cats which includes eosinophilic granulomas, eosinophilic plaques, and miliary dermatitis	Ulcer forms on the upper lip; ulcer can be very deep	Skin scrapings, biopsy	Steroids; sometimes antibiotics; look for underlying cause
Sebaceous gland tumor	Rare in cats; rarely spreads or recurs; several types	Nodules which may ulcerate; usually on the head and legs	Biopsy	Surgical removal if invasive; if a benign lesion, removal is optional
Skin cancer	See specific type, e.g., Fibrosarcoma, Melanoma, Squamous cell carcinoma, Mast cell tumor, Lymphoma
Skin fold pyoderma (intertrigo)	Inflammation of skin that contacts other skin, e.g., lips, facial folds (on Persians, for instance), vulva, tail, toes, and bodies of obese cats	Red, oozing area; crusts; often becomes infected and may develop odor	Clinical signs; skin scrapings and tape impression smears	Clip and cleanse area; keep area clean; medicated shampoos; topical antibiotics; treat underlying condition, e.g., increased tears from eye disease, obesity, allergy
Solar dermatosis (sunburn)	Skin reaction to sunlight; more common in cats with white ears	Redness, hair loss, and scaling on nose and ears, later crusts and ulcers	History, breed, physical exam, skin biopsy	Must avoid further sun exposure, especially 9 am - 3 pm; sunblock, steroids
Spider bites/eosinophilic folliculitis	Bites from some spiders and caterpillars contain strong toxins; usually appear on the nose of dogs and paws of cats	Immediately after the bite, swelling, redness, pain; subsequently may develop extensive ulcers with draining	History, biopsy	Corticosteroids, wet dressings, protect the area from self-inflicted trauma; may develop permanent loss of hair and scarring
Sporotrichosis	Caused by the fungus Sporothrix schenckii which generaly enters through a puncture wound	Raised nodules with multiple draining tracts; cats may develop fever, depression, and loss of appetite	Microscopic exam of drainage; culture; fluorescent antibody test	Potassium iodide, ketoconazole, itraconazole
Squamous cell carcinoma	Common malignant tumor; may occur more commonly in sun-damaged or chronically irritated skin	Two forms: cauliflower-like lesions, often ulcerated more common on ears; crusted ulcers on head or feet (around claws)	Biopsy	Surgical removal, radiation, hyperthermia
Stud tail (tail gland hyperplasia)	A sebaceous gland (on the top of the tail near its base) enlarges; most often occurs in confined, unneutered males	Oily area, hair loss, and crusts on area over gland; may become hyperpigmented	Clinical signs	Castration usually does not resolve the condition; antiseborrheic shampoos, retinoids; if confined, allow cat more freedom
Tick bites	Ticks cause a local inflammation in the skin, even when the entire tick is removed	Nodule and redness at site of the bite; may itch and develop crusts; may last several months	History	Remove the tick; use a tick preventative; allow nodule to resolve on its own
Toxic epidermal necrolysis	Severe immune reaction to infections or drugs; may also be caused by cancer or other diseases	Vesicles, erosions, ulcers, crusts over large areas of the body, especially mouth and feet; may look like a severe burn	History, clinical signs, skin biopsy	Prognosis is poor; treat underlying condition; give supportive care, corticosteroids may be helpful
Urine scald	Occurs when skin is in prolonged contact with urine, e.g., recumbent cats	Red, oozing lesions in areas exposed to urine	History, clinical signs	Clip and cleanse area; keep it clean; place cat on wire or plastic rack or grate; change bedding often; medicated shampoos; topical antibiotics
Zygomycosis	Uncommon fungal disease	Draining nodules; may also see pneumonia, vomiting, or jaundice depending upon the body organs involved	Microscopic examination of the drainage; biopsy	Often fatal; surgical removal of nodules followed by amphotericin B, benzimidazoles, or potassium iodide

* off-label use: medication used to treat a condition for which it was not developed (or licensed). A large number of medications fall under this category. Research has almost always been performed to determine the effectiveness and safety of the product, but the manufacturer has not undertaken the lengthy process required for licensure.