• In every patient with alopecia
  • To look for broken hair tips when one suspects self-induced alopecia
  • To determine if hairs are in anagen or telogen phase (the interpretation of ratios of telogen hairs to anagen hairs in dogs is breed and season-dependent and exact ratios have not been established)
  • When dermatophytosis is suspected
  • To identify dogs with color dilute haircoats
  • As an alternative to a deep skin scraping when Demodex is suspected


  • Broken off hair tips → caused by self-trauma
  • Tapered hair tips → hair loss is caused by events within the follicle e.g. endocrine disorders or inflammation involving the hair follicle
  • Hairs in anagen (growing) phase → roots of anagen hairs are rounded, curled, bent and often smooth and pigmented
  • Hairs in telogen (resting) phase → roots of telogen hairs are lancet-shaped and lack pigmentation, although the base of the hair may show a roughened or brush-like edge
  • The presence of numerous anagen phase hairs should decrease the suspicion for an endocrinopathy
  • In the case of dermatophytosis, affected hairs are covered with spores and penetrated by hyphae
  • Color dilution alopecia→ melanin is clumped in the hair shaft
Photo of dog with demodicosis
Sampling hairs for a trichogram (Courtesy of Sonya Bettenay)
Photo of Focal alopecia due to demodicosis
Trichogram with pointy hair tips (Courtesy of Sonya Bettenay)
Photo of Squeeze skin
Trichogram with broken off hair tips (Courtesy of Sonya Bettenay)
Photo of scrape until light capillary oozing
Hair bulbs in anagen phase (Courtesy of Sonya Bettenay)
Photo of excoriation after deep skin scraping
Hair bulbs in telogen phase (Courtesy of Sonya Bettenay)
Micrograph of <em>Demodex</em> mites, adults and juvenile forms
Demodex canis: two adult mites and one larva on a hair bulb (Courtesy of Francesco Albanese and Frederico Leone)
Micrograph of <em>Demodex</em> mites, larvae and eggs
Dermatophyte spores in the hair
SMicrograph of <em>Demodex canis</em>
Color dilution alopecia – macromelanosomes (Courtesy of Francesco Albanese)

What do I need?

  • Forceps/hemostat or rubber covered clamp, mineral oil, slide, cover slip, microscope

How do I do it?

  • Pluck a small number of hairs in a partially or completely alopecic area using forceps/clamp in direction of hair growth; hold the forceps/clamp close to the skin surface and grasp all hair shafts which emerge
  • Put a drop of mineral oil onto a slide, place the hairs in parallel order on the mineral oil, separate them to evaluate roots and tips adequately
  • Cover hairs with a cover slip and evaluate with the microscope


  • Cover the tips of your forceps or clamp with rubber or silicon sleeves to avoid crushing or breaking the hair shafts.
  • You can also use the trichogram technique to look for Demodex mites in affected areas that are difficult to scrape (e.g. close to the eye, pododermatitis). Ideally a 1-2 cm2 area will be plucked, the same area as with a skin scraping.
  • You might find Demodex mites hanging on the hairs or sometimes hiding behind them. Only positive results are diagnostic.
  • You can also find lice, Cheyletiella mites and their eggs.


A discrete swelling containing purulent material, typically in the subcutis

Photo of abscess

Perianal abscess in a dog


Absence of hair from areas where it is normally present; may be due to folliculitis, abnormal follicle cycling, or self-trauma

Photo of alopecia

Extensive alopecia secondary to cutaneous epitheliotropic lymphoma

alopecia (“moth-eaten”)

well-circumscribed, circular, patchy to coalescing alopecia, often associated with folliculitis

Photo of alopecia (“moth-eaten”)

“Moth-eaten” alopecia secondary to superficial bacterial folliculitis


Regional subcutaneous edema

Photo of angioedema

Angioedema due to cutaneous drug eruption


Ring-like arrangement of lesions

Photo of annular

Annular lesions in a dog with erythema multiforme


Thinning of the skin or other tissues

Photo of atrophy

Cutaneous atrophy due to glucocorticoids


Fluid-filled elevation of epidermis, >1cm

Photo of bulla

Bullae in a dog with bullous pemphigoid

hemorrhagic bullae

Blood-filled elevation of epidermis, >1cm

Photo of hemorrhagic bullae

Interdigital hemorrhagic bulla in a dog with deep pyoderma and furunculosis


dilated hair follicle filled with keratin, sebum

Photo of comedo

Comedones on the ventral abdomen of a dog with hypercortisolism


Dried exudate and keratinous debris on skin surface

Photo of crust

Multifocal crusts due to pemphigus foliaceus


Nodule that is epithelial-lined and contains fluid or solid material.

Photo of cyst

Epidermal inclusion cyst


Extensive loss of pigment

Photo of depigmentation

Depigmentation of planum nasale in dog with vitiligo.


Patches due to hemorrhage >1cm

Photo of ecchymoses

Ecchymoses of a dog’s leg due to vasculitis

epidermal collarettes

Circular scale or crust with erythema, associated with folliculitis or ruptured pustules or vesicles

Photo of epidermal collarettes

Epidermal collarettes in a dog with Staphylococcus superficial bacterial folliculitis


Defect in epidermis that does not penetrate basement membrane. Histopathology may be needed to differentiate from ulcer.

Photo of erosion

Erosions in a dog with vasculitis


Red appearance of skin due to inflammation, capillary congestion

Photo of erythema

Erythema in a dog with cutaneous drug eruption


Thick crust often related to necrosis, trauma, or thermal/chemical burn

Photo of eschar

Eschar from physical trauma


Erosions and/or ulcerations due to self-trauma

Photo of excoriation

Excoriations in a cat with atopic dermatitis


Excessive stratum corneum, confirmed via histopathology. This term is often used to describe the nasal planum and footpads.

Photo of fissure

Fissures of the footpads in a dog with superficial necrolytic dermatitis


Ulcer on skin surface that originates from and is contiguous with tracts extending into deeper, typically subcutaneous tissues

Photo of fistula

Perianal fistulas in a dog

follicular casts

Accumulation of scale adherent to hair shaft

Photo of follicular casts

Follicular casts surrounding hairs from a dog with hypothyroidism


Excessive stratum corneum, confirmed via histopathology. This term is often used to describe the nasal planum and footpads.

Photo of hyperkeratosis

Idiopathic hyperkeratosis of the nasal planum (left) and footpads (right)


Increased melanin in skin, often secondary to inflammation

Photo of hyperpigmentation

Inflammatory lesions (left) resulting in post-inflammatory hyperpigmentation (right)


Partial pigment loss

Photo of hypopigmentation

Idiopathic hypopigmentation of planum nasale


Lack of hair due to genetic factors or defects in embryogenesis.

Photo of hypotrichosis

Congenital hypotrichosis in chocolate Labrador puppies.


Lack of cutaneous pigment

Photo of leukoderma

Macular leukoderma in a dog


Loss of hair pigment

Photo of leukotrichia

Progressive leukotrichia in patient with vitiligo.


Thickening of the epidermis, often due to chronic inflammation resulting in exaggerated texture

Photo of lichenification

Lichenification of skin in a dog with chronic atopic dermatitis and Malassezia dermatitis


Flat lesion associated with color change <1cm

Photo of macule

Pigmented macule (left) Erythematous macule (right)


Increased melanin in skin, may be secondary to inflammation.

Photo of melanosis

Post inflammatory hyperpigmentation of this dog’s thigh


Multifocal, papular, crusting dermatitis; a descriptive term, not a diagnosis

Photo of miliary

Miliary dermatitis in a flea allergic cat


A erythematous, macular, papular rash; the erythematous macules are typically 2-10 mm in diameter with coalescence to form larger lesions in some areas

Photo of morbiliform

Morbiliform eruptions in a dog with a cutaneous drug reaction


A solid elevation >1cm

Photo of nodule

Nodules on nose of dog with cutaneous histiocytosis.


Abnormal nail morphology due to nail bed infection, inflammation, or trauma; may include: Onychogryphosis, Onychomadesis, Onychorrhexis, Onychoschizia

Photo of onychodystrophy

Onychodystrophy in dog with chronic allergies


Abnormal claw curvature; secondary to nail bed inflammation or trauma

Photo of onychogryphosis

Onychogryphosis in a dog with symmetric lupoid onychodystrophy


Claw sloughing due to nail bed inflammation or trauma

Photo of onychomadesis

Onychomadesis in a dog with symmetric lupoid onychodystrophy


Claw fragmentation due to nail bed inflammation or trauma

Photo of onychorrhexis

Onychorrhexis in a dog with symmetric lupoid onychodystrophy


Claw splitting due to nail bed inflammation or trauma

Photo of onychoschizia

Onychoschizia in a dog with symmetric lupoid onychodystrophy


Solid elevation in skin ≤1cm

Photo of papule

Papules on a dog with superficial bacterial folliculitis


Solid elevation in skin ≤1cm

Photo of papules

Papules on a dog with superficial bacterial folliculitis


Inflammation of the nail fold

Photo of paronychia

Paronychia in a dog with symmetric lupoid onychodystrophy


Flat lesion associated with color change >1cm

Photo of patch

Hypopigmented patch (left), erythematous patch (right)


Small erythematous or violaceous lesions due to dermal bleeding

Photo of petechiae

Petechiae in a dog with cutaneous vasculitis


Venous dilation; most commonly associated with hypercortisolism

Photo of phlebectasia

Phlebectasia and cutaneous atrophy due to hypercortisolism in a dog


Flat-topped elevation >1cm formed of coalescing papules or dermal infiltration

Photo of plaques

Plaques in a cat with cutaneous lymphoma


Raised epidermal infiltration of pus

Photo of pustule

Pustules on the abdomen of a dog with superficial staphylococcal pyoderma.


Net-like arrangement of lesions

Photo of reticulated

Reticulated leukotrichia on the back of a horse


Accumulation of loose fragments of stratum corneum

Photo of scale

Loose, large scales due to ichthyosis in a Golden Retriever


Fibrous tissue replacing damaged cutaneous and/or subcutaneous tissues

Photo of scar

Scarring (right) following the healing of an ulcer (left) in a dog with sterile nodular dermatitis


Undulating, serpentine (snake-like) arrangement of lesions

Photo of serpiginous

Serpiginous urticarial lesions on a horse


Permanent enlargement of vessels resulting in a red or violet lesion (rare)

Photo of telangiectasia

Telangiectasia in a dog with angiomatosis


A defect in epidermis that penetrates the basement membrane. Histopathology may be needed to differentiate from an erosion.

Photo of ulcer

Ulcerations of the skin of a dog with vasculitis.


Wheals (steep-walled, circumscribed elevation in the skin due to edema ) due to hypersensitivity reaction

Photo of urticaria

Urticaria in a horse


Fluid-filled elevation of epidermis, <1cm

Photo of vesicle

Vesicles and bullae on ear pinna due to bullous pemphigoid


Steep-walled, circumscribed elevation in the skin due to edema

Photo of wheal

Wheals associated with intradermal allergy testing in a horse