ACVD Veterinary Dermatology key terms

A dilated hair follicle plugged with keratin and sebum that appears as a blackhead; a primary lesion of feline acne and canine sebaceous adenitis, formed when follicular keratinization is abnormal.

The normal maturation and shedding of cells lining the hair follicle; when disordered it produces comedones, follicular casts, or plugged follicles and underlies many keratinization disorders.

A cylindrical accumulation of keratin and cellular debris that clings to the hair shaft and is visible as a sheath when hairs are plucked; a hallmark of keratinization defects and demodicosis.

A ring of peeling stratum corneum that surrounds a healing or expanding skin lesion, often indicating a previous pustule or vesicle; typical of superficial pyoderma and immune-mediated diseases.

A small, circumscribed, pus-filled elevation of the epidermis or hair follicle; its contents and location help distinguish infectious from sterile (immune-mediated) causes.

A small, solid, raised skin lesion less than about one centimeter in diameter without visible fluid; a primary lesion of many inflammatory and infectious dermatoses.

A flat, circumscribed area of altered skin color, not raised and not palpable; examples include pigmented spots and erythematous patches of early inflammation.

Redness of the skin caused by dilation of superficial blood vessels; it blanches with pressure and is a nonspecific sign of inflammation, infection, or allergy.

Thickening of the epidermis with exaggerated skin markings, producing a leathery, hyperpigmented appearance from chronic rubbing or scratching; common in chronic allergic dermatitis.

Increased melanin deposition in the epidermis or dermis that darkens the skin; often follows chronic inflammation, endocrine disease, or post-inflammatory change.

The sensation that provokes the urge to scratch; a central clinical feature used to classify dermatoses and to judge response to therapy in allergic and parasitic disease.

A genetically predisposed tendency to develop immunoglobulin E-mediated hypersensitivity to environmental allergens, producing pruritic dermatitis in dogs and cats.

A diagnostic procedure in which small amounts of allergens are injected into the skin and wheal responses are measured to identify allergens relevant to a patient's hypersensitivity.

Measurement of allergen-specific immunoglobulin E in blood to support a diagnosis of allergic skin disease; results must be interpreted alongside clinical history, not used alone.

A hypersensitivity reaction to flea saliva antigens that causes intense pruritus and lesions concentrated over the caudal body and dorsal lumbosacral area.

Systematic examination of hair and skin with a fine-toothed comb to detect fleas and flea feces; a simple, inexpensive step in evaluating pruritic dermatoses.

A cigar-shaped mite that normally inhabits hair follicles of mammals; excessive proliferation, often linked to immune dysfunction, causes demodicosis with alopecia and follicular casts.

A diagnostic technique that squeezes the skin and scrapes until capillary blood appears, sampling material from deep follicles to detect Demodex mites and other organisms.

Microscopic examination of stained smears of cells and debris collected from skin, ear canals, or lesions; used to identify bacteria, yeast, mites, and inflammatory cell types.

Bacterial infection confined to the epidermis and hair follicles, typically caused by Staphylococcus species and producing papules, pustules, collarettes, and crusts.

Bacterial infection extending into the dermis and deeper tissues, causing nodules, draining tracts, and fistulas; often requires prolonged systemic antimicrobial therapy and investigation of underlying causes.

Laboratory determination of which antimicrobial drugs inhibit growth of an isolated organism, used to guide therapy when resistance is suspected or deep infection is present.

Yeast overgrowth of the skin caused by Malassezia species, producing greasy, erythematous, pruritic, often malodorous lesions; frequently secondary to allergy or endocrine disease.

A keratinophilic fungus that infects hair, nails, and stratum corneum, causing dermatophytosis with circular alopecic, scaly lesions and broken hairs.

An ultraviolet lamp used to screen for certain dermatophyte infections that fluoresce apple-green; a positive result supports diagnosis but a negative result does not exclude infection.

Inoculation of clinical material onto selective media to grow and identify dermatophytes; considered the reference method for confirming dermatophytosis.

A burrowing mite that causes sarcoptic mange, an intensely pruritic and contagious dermatitis with papules and crusts, often on ear margins and elbows.

A surface-dwelling ear mite of dogs and cats that causes otitis externa with dark ceruminous debris and intense scratching of the ears and head.

Inflammation of the external ear canal, recognized by erythema, discharge, and discomfort; often driven by underlying allergy, anatomy, or infection.

Disease of an endocrine gland, such as hypothyroidism or hyperadrenocorticism, that produces characteristic skin changes including alopecia, hyperpigmentation, and secondary infection.

Partial or complete loss of hair from areas where it normally grows; classified as inflammatory or noninflammatory and as focal or generalized to guide diagnostic testing.

An inflammatory disease of sebaceous glands that destroys them, causing scaling, follicular casts, alopecia, and comedones, especially in certain predisposed breeds.

An autoimmune skin disease in which antibodies target epidermal desmosomes, causing pustules, crusts, and scaling; a principal differential for sterile pustular dermatitis.

Surgical collection of skin tissue for histopathologic examination; essential for diagnosing immune-mediated, neoplastic, and unusual dermatoses that cannot be resolved by surface testing.

Feeding a restricted or hydrolyzed diet for several weeks while avoiding other foods, to identify food-induced allergic dermatitis by observing improvement and relapse on challenge.

Use of corticosteroid drugs to suppress inflammation and pruritus; requires monitoring because it can worsen infection and mimic or cause endocrine skin changes.

An infectious disease transmissible between animals and people; relevant dermatologic examples include dermatophytosis, sarcoptic mange, and some bacterial infections.