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Causes of Solid-Appearing Lumps & Bumps on the Skin of Dogs
Veterinary & Aquatic Services Department, Drs. Foster & Smith
Skin Conditions
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Dogs and cats can develop small bumps (papules) or larger lumps (nodules) on their skin. The term 'tumor' means an abnormal growth or swelling, and is often used to designate cancer. Often, the word 'lump' also brings the word 'cancer' to mind. There are, however, many other causes of lumps and bumps. The following table includes most of the conditions which result in solid lumps and bumps. The list is rather extensive, so you can understand why a quick diagnosis may be difficult to make and various diagnostic tests, such as biopsies, may need to be performed. The most common causes of solid lumps and bumps 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 or fluid-filled nodules of varying shapes and sizes; if due to infection, the animal may have fever, loss of appetite, and depression; may open and drain History, physical exam, needle aspirate Surgically open, drain and flush; if infected, administer appropriate antibiotics

Acral lick dermatitis (neurodermatitis)

Self-licking in dogs results in self-trauma; possible causes include anxiety, boredom, stress (e.g., new member in household); licking can develop into an obsessive behavior

Red, hairless, well-circumscribed, sometimes raised lesion usually on leg; if chronic, will drain

Exclude other causes; history important

Relieve underlying cause e.g., anxiety; restrict licking, e.g., Elizabethan collar; behavior modifying medication may be necessary

Allergic and irritant contact dermatitis

An allergic reaction following exposure to antibiotics applied to the skin; metals such as nickel; materials such as rubber, wool, and plastic; and chemicals such as dyes and carpet deodorizers; or inflammation caused by irritating substances such as poison ivy. Generally requires multiple exposures.

Red skin and small bumps or blisters on the areas of skin that are sparsely haired and directly exposed to the offending substance; itching; hair loss in chronic conditions

Patch test, exclusion trials

Restrict exposure to the allergen or contact irritant in the dog's environment; steroids, antihistamines

Apocrine sweat gland cyst Common Single, round, smooth nodules with no hair; may appear bluish; usually filled with a watery liquid; most common on head, neck, and limbs Physical exam; biopsy Surgical removal is optional
Basal cell tumors Cancerous, slow-growing tumor which rarely metastasizes; seen in older dogs Single, sometimes fluid-filled nodules, which may ulcerate; usually on the head, neck, and chest; may be hyperpigmented Biopsy Surgical removal
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
Benign tumors See specific type, e.g., Fibromas, Lipomas, Histiocytomas, Basal cell tumor      
Calcinosis cutis Mineralization of the skin usually due to an excess of corticosteroids; also rarely occurs in kidney failure, or in granulomas and tumors Hard nodules and papules usually on the back, groin, or axilla ulcerate, drain, and develop crusts; severe itching; may become infected; often see other signs of Cushing's disease Skin scrapings, biopsy, history, and other clinical signs, adrenal gland function tests If due to glandular tumors, selegiline, o,p-DDD (Mitotane), or surgical removal of tumor; if due to high steroid doses, withdraw use of steroids slowly
Callus Results from chronic pressure, especially in large breed dogs Thickened, hairless raised areas over bony pressure points such as elbows; may become secondarily infected History, clinical signs Provide softer bedding and padding around affected area
Canine acne Deep inflammation of hair follicles; exact cause unknown; usually in young dogs; may see secondary bacterial infection Papules, and sometimes draining lesions on chin and lips Skin biopsy Mild: Benzoyl peroxide; Severe: Also treat with antibiotics

Chiggers (harvest mites)

Seasonal disease caused by larvae of the chigger

Itching, bumps usually on feet, abdomen (belly), folds at base of ears

Visualization of mite larvae or microscopic examination of skin scraping

Pyrethrin, Permethrin (Do NOT use permethrin on cats.)

Coccidioidomycosis Caused by the fungus Coccidioides immitis found in the soil in the Southwestern U.S. Draining nodules over infected bones; usually see respiratory signs, fever, weight loss Microscopic examination of drainage; blood tests Ketoconazole, itraconazole
Cryptococcosis Fungal infection often transmitted through bird droppings; more common in dogs 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
Cutaneous horn Benign growths of hard tissue, which look like small horns; cause unknown, though may be associated with some underlying disease such as cancers or follicular cysts ½ to 2 inch hard horn-like growths; may be single or multiple; in cats, may occur on foot pads Clinical appearance; look for underlying cause Surgical removal
Cuterebra Caused by the 1-1½ inch larva of the Cuterebra fly; usually seen in late summer Nodule forms around the larva; usually found on the head and neck; nodule has a small opening through which the larva breathes and will eventually escape Clinical signs; opening the nodule and finding the larva Surgically open the nodule and remove the larva; do NOT squeeze the nodule or break up the larva or a severe allergic reaction may occur
Dracunculiasis Nodule formed around the parasitic worm Dracunculus insignis (Guinea worm) Single or multiple nodules on limbs, head, and belly; nodules may drain Clinical signs; opening nodule and finding the female worm (1-4 feet in length!) Surgical removal
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
Epidermal inclusion cysts (infundibular cysts) Result from body's reaction to certain skin cells Very small, up to 2 inch diameter nodules, which often contain thick sebaceous material Needle aspirate, histopathology on removed nodule Surgical removal may be performed, although new nodules will often form elsewhere; do NOT squeeze these cysts, since a more severe skin reaction will occur
Epitheliotropic lymphoma (mycosis fungoides) Rare cancer of T lymphocytes seen in older dogs Can take multiple forms: redness with itching and scale; ulcers and loss of pigment; one or more nodules; oral ulcers Needle or other biopsy Poor response to treatments, which include chemotherapy, surgical removal, retinoids, fatty acids
Fibroma Uncommon benign tumor Single nodule with a pedicle, usually on legs, groin, or sides Biopsy Surgical removal is optional
Fibrosarcoma Rapidly growing, invasive tumor; may occur at the site of a vaccination or injection 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 dog 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 dog; steroids and antihistamines for the itching

Follicular cyst Most common cyst; may be called 'sebaceous cysts' by some veterinarians Single round nodules on or underneath the skin; may appear bluish; may contain a thick, yellowish to gray material; usually found on the head, neck, and trunk Biopsy Surgical removal optional; do NOT squeeze these cysts, since a severe skin reaction will occur
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 chest or abdomen; 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
Hematoma Localized collection of blood that has leaked out of blood vessels; often occurs in dogs with ear infections and pendulous ears These may appear as firm or fluid-filled nodules of varying shapes and sizes Needle aspirate Depending on location and size, may resolve on their own, or need drainage (e.g., on ear flap)
Histiocytoma Benign tumor of younger dogs Solitary raised, red nodules with a strawberry-like appearance; usually on the legs, head, and ears Needle aspirate, biopsy Generally resolve on their own; can be surgically removed
Histiocytosis There are several kinds of histiocytosis: Malignant, which is a cancer that affects the skin and internal organs; Systemic, which is a rare disease which affects skin and internal organs; Cutaneous, which is a benign disease affecting the skin All cause nodules with hair loss; malignant and systemic also have ulcers Biopsy, fine needle aspirate; Malignant: None effective, may need to consider euthanasia; Systemic: Poor response to chemotherapy; Cutaneous: Corticosteroids, relapse is common, especially in Shar-Peis
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


Infection with the larvae (immature forms) of hookworms

Red bumps, usually on feet, rough foot pads, abnormal nail growth, itching

Physical exam, history of poor sanitation

Treat for intestinal infection; move dog to different environment

Infundibular keratinizing acanthoma Rare benign nodules more common in young Norwegian Elkhounds One or more small to 1½ inch nodules, with small opening through which thick material can be expressed Biopsy Surgical removal; retinoids, if multiple lesions
Kerion Complication of ringworm infection Nodule with hair loss and multiple draining tracts; may not see other signs of ringworm Culture, biopsy Clip area and apply topical treatment and shampoos; may require systemic treatment with ketoconazole or itraconazole
Leishmaniasis Caused by a parasite of blood cells; can be transmitted to people who develop a very severe disease Hair loss, scaling, ulcers on nose and ears, sometimes nodules; many other nonskin-related signs Identify the organism in blood or biopsy; blood tests Because it causes severe disease in people, and treatment of dogs is not curative, euthanasia may be performed
Lichenoid dermatosis Often a response to other underlying disease such as fleas or bacterial infections Small flat nodules with thick surfaces Biopsy, look for underlying disease Treat underlying cause; this reaction usually resolves on its own
Lipoma Uncommon benign fatty tumor Usually single, soft, domed nodule; can become very large Fine needle biopsy Surgical removal, if large or interferes with movement


Common cancer in dogs; can involve the skin

Itching, ulcers, nodules, redness


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 dogs, 50% 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 slow-growing tumors, and Grade 4 is rapidly growing malignant tumors with metastases 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 of older dogs Usually single dark-colored nodule, which often ulcerates Biopsy Surgical removal, taking large area around tumor
Nevi Usually benign lesions; some types may indicate the presence of an underlying disease Well-delineated firm nodules, often multiple and on the head and neck Biopsy Surgical removal, although recurrence is common; depending upon the type, look for underlying disease
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
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

Pelodera dermatitis

Accidental infection with larvae from a non-parasitic worm that lives in straw and other organic material

Affects areas of skin touching ground; intense itching, redness, hair loss, papules, crusts, and scales

Skin scraping and microscopic examination

Remove bedding; mild antibacterial shampoo; steroids if necessary, to control itching

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 recurs; possible antifungal medications
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, and thickened skin Skin scrapings, biopsy, culture Clip and cleanse area; antibiotics, prevent self-trauma (licking, scratching), NO Steroids
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


Infection with several types of fungus

Hair loss, scaliness, crusty areas, pustules, and vesicles, some itching; can develop a draining nodule called a 'kerion'


Miconazole, lime sulfur dips; oral griseofulvin or itraconazole

Sarcoptic mange

Infection with the Sarcoptes mite

Intense itching and self-trauma, hair loss, papules, crusts, and scales

Skin scraping and microscopic examination - the mite is often very difficult to find

Amitraz (Mitaban) dips (off-label use*); ivermectin (off-label use*)

Schnauzer comedo syndrome Uncommon; only seen in Miniature Schnauzers Comedones (black heads) on back, mild itching; may see secondary infection, thinning of hair; small crusts may develop Clinical signs, breed, skin biopsy Long-term antiseborrheic shampoos; sometimes antibiotics and retinoids
Sebaceous gland cyst Extremely rare Firm nodules, usually less than ½ inch in diameter Biopsy Surgical removal
Sebaceous gland tumors Common; rarely spread or recur; 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      
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 generally 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 lips and nose; Crusted ulcers on limbs or body Biopsy Surgical removal, radiation, hyperthermia
Superficial necrolytic dermatitis of Miniature Schnauzers Skin reaction to shampoos (usually insecticidal or medicated) Papules, pustules, and ulcers with drainage; develop 2-3 days after exposure to the shampoo; may also see fever and depression Breed, history of exposure, clinical signs Treat symptomatically
Tail dock neuroma Nerve regrowth after tail docking causes symptoms Nodule at site of docking, itching with self-mutilation, hair loss, and hyperpigmentation History and symptoms Surgical removal
Tail gland hyperplasia Dogs have a sebaceous gland on the top of the tail near its base; in this disorder, the gland enlarges; seen in unneutered dogs and secondary to other diseases such as hypothyroidism Oily area, hair loss, crusts, and hyperpigmentation on area over gland Clinical signs; look for underlying cause Castration may help; treat underlying cause; surgical removal
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 preventive; allow nodule to resolve on its own
Urticaria (hives) Reaction, often allergic, to insect bite, drug, vaccine, sunlight, etc. Multiple swellings, with hair standing up over swellings; itching may occur History, physical exam Often resolves on its own; in the case of allergic reactions, antihistamines, epinephrine, or corticosteroids depending upon severity
Warts (cutaneous papilloma) Benign growths caused by a virus; usually seen in puppies Light-colored growths with a cauliflower appearance; usually on the lips, tongue, inside of the mouth, and eyelids Clinical appearance, biopsy Usually none - they resolve by themselves; if severe, removal by cryosurgery
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


References and Further Reading

Birchard, SJ; Sherding RG (eds.) Saunders Manual of Small Animal Practice. W.B. Saunders Co. Philadelphia, PA; 1994.

Greene, CE (ed.) Infectious Diseases of the Dog and Cat. W.B. Saunders Co. Philadelphia, PA; 1998.

Griffin, C; Kwochka, K; Macdonald, J. Current Veterinary Dermatology. Mosby Publications. Linn, MO; 1993.

McKeever, PJ; Harvey, RG. Skin Diseases of the Dog and Cat. Iowa State University Press. Ames, Iowa; 1998.

Paterson, S. Skin Diseases of the Cat. Blackwell Science Ltd. London, England; 2000.

Paterson, S. Skin Diseases of the Dog. Blackwell Science Ltd. London, England; 1998.

Scott, D; Miller, W; Griffin, C. Muller and Kirk's Small Animal Dermatology. W.B. Saunders Co. Philadelphia, PA; 1995.

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