| 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
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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
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| 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 |
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| 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.)
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| 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
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| 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 |
Hookworms
| 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
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| 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 |
Lymphoma
| Common cancer in dogs; can involve the skin
| Itching, ulcers, nodules, redness
| Biopsy
| Surgery, chemotherapy, radiation; lymphoma of the skin does not usually respond to treatment as well as other lymphomas
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| 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
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| 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 |
Ringworm
| Infection with several types of fungus
| Hair loss, scaliness, crusty areas, pustules, and vesicles, some itching; can develop a draining nodule called a 'kerion'
| Culture
| Miconazole, lime sulfur dips; oral griseofulvin or itraconazole
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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*)
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| 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 |
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| 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 |
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