Causes of Fluid-filled Bumps on the Skin of Dogs
Veterinary & Aquatic Services Department, Drs. Foster & Smith

Small bumps on the skin which are filled with pus are called 'pustules.' Larger bumps filled with pus are abscesses. If small bumps contain a clear fluid, they are called 'vesicles.' There are many conditions which can cause these lesions, and most of them are included in the table below. The number of conditions is extensive, so you can 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 fluid-filled 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, depression; may open and drain History, physical exam, needle aspirate Surgically open, drain, and flush; if infected, administer appropriate antibiotics

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

Bacterial Infection (Pyoderma)

See Impetigo, Folliculitis, Staph hypersensitivity, Pyoderma-deep

Often occurs as a result of another condition such as a parasite, allergic, or hormonal condition

Canine distemper (hard pad disease) With vaccinations, canine distemper has become rare in many areas; foot pad lesions are common in this disease Puppies may develop impetigo; thickening of the end of the nose and foot pads; also see other signs of illness associated with distemper History of no vaccination; physical exam; blood tests to detect antibody response to viral infection Supportive treatment; may be fatal or result in permanent problems
Cutaneous mucinosis Secondary to other diseases; more common in young Shar-Peis Vesicles filled with thick fluid Biopsy Treat underlying disease; Shar-Peis usually outgrow condition; severe cases - prednisone

Demodectic mange (red mange, puppy mange)

Infection with the Demodex mite - occurs when the immune system is deficient

Hair loss, scaliness, redness, pustules, ulcers, sometimes itching, darkening of the skin

Skin scraping and microscopic examination

NO Steroids

Amitraz (Mitaban) dips

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
Folliculitis Infection of the hair follicles, often with staph bacteria; symptoms usually appear on skin with less hair, such as the abdomen (belly) Pustules form in follicles and break open to form 'bull's-eye,' 'annular,' and 'target lesions,' which have crusty centers and red or darkening on the periphery, and 'epidermal collarettes,' which appear as rings of scaly skin; itching may occur; short-coated breeds may develop small tufts of hair which are lost; breeds with long coats may have seborrhea Skin scraping; culture; biopsy Antibiotics for at least 4 weeks - continue antibiotics 10 days beyond the apparent cure; if recurs, look for underlying problem such as allergy or hormonal imbalance
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)
Impetigo Usually affects puppies less than one year of age; often a Staph infection Localized area of small pustules - especially on the abdomen crusts, circular areas of scaling History and physical exam; bacterial culture; skin scraping Topical hydrogen peroxide; chlorhexidine or benzoyl peroxide shampoos; antibiotics, if serious; puppies usually outgrow it
Lupus erythematosus Autoimmune disease affecting many body systems including 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
Nasal pyoderma (furunculosis) Deep infection of the bridge of the nose Papules, pustules, deep ulcers, draining tracts; often results in scarring Skin scraping; bacterial and fungal culture; biopsy; look for underlying cause, e.g., 'rooting around' with nose Clip and clean area; long-term antibiotics; prevent further trauma (e.g; Elizabethan collar); NO Steroids
Pemphigus, bullous pemphigoid Rare autoimmune condition, most often seen in Collies and Doberman Pinschers 80% of dogs have oral lesions; vesicles in groin area and underneath front legs History, physical exam, biopsy Steroids and other immunosuppressants
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 steroids; other immunosuppressives
Pemphigus foliaceus The most common form of pemphigus in the dog; an autoimmune disease; some breeds are at increased risk 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 animals 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; pemphigus vegetans is a milder form of this disease seen in dogs Large vesicles which break open, ulcerate, and develop thick crusts; lesions often found in the mouth Biopsy Poor prognosis; prednisolone and other immunosuppressants
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

See Impetigo, Folliculitis, Staph hypersensitivity



Infection with several types of fungus

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


Miconazole, lime sulfur dips; oral griseofulvin or itraconazole

Staph hypersensitivity Rare disease in dogs caused by an allergic reaction to the bacteria Staphylococcus; often occurs in the presence of other skin diseases Red skin, pustules, vesicles, severe itching, and sometimes crusts Culture, biopsy, intradermal allergy test Treat any underlying disease; antibiotics
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
Toxic epidermal necrolysis Severe immune reaction to infections or drugs; may also be caused by cancer or other diseases Vesicles, erosions, ulcers, and 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
Ulcerative dermatosis of Collies and Shetland Sheepdogs May be a type of dermatomyositis; cause unknown; seen in middle-age or older dogs Large vesicles and ulcers on groin, axilla, eyelids, ears, genitals, anus, and foot pads; painful Breed, physical exam, biopsy Avoid trauma; antibiotics if secondary infection; Vitamin E, fatty acids, short-term use of prednisone, oxpentoxifylline

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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