Trichogram Analysis in Dogs: What Hair Plucking Reveals About Skin Disease

By Emiel Maddens · Reviewed in consultation with licensed veterinary professionals · Updated August 2026 · 9 min read

What Is a Trichogram in Dogs?

A trichogram is a microscopic examination of hairs plucked from a dog's coat, used to evaluate hair shaft structure, root morphology, and any organisms or pigment abnormalities attached to the hair. It is one of the fastest and least invasive tests in veterinary dermatology, and it answers a question that visual inspection alone cannot: is this dog losing hair, or is this dog removing hair?

The distinction matters more than most owners expect. Self-induced alopecia, where a dog licks, chews, or scratches hair away, and spontaneous alopecia, where the follicle stops producing hair, look nearly identical on the surface. Both present as thinning, bald patches, or a moth-eaten coat. Under magnification they separate immediately. Hair that fell out on its own ends in a smooth, tapered, or club-shaped tip. Hair that was chewed off ends in a blunt, splintered fracture, often described as a broom or paintbrush end.

A standard trichogram examines 30 to 50 hairs per site, mounted in mineral oil under a coverslip and read at 4x to 10x magnification for shafts and tips, then 40x for roots and organisms. Most general practices can perform it chairside during the same appointment. The American College of Veterinary Dermatology has long recommended it as part of the minimum database for any alopecic dog, alongside skin scrapings and cytology.

The technique is grossly underused. In one survey of small animal practitioners, fewer than one in three reported routinely performing trichograms on alopecic patients, despite the test requiring no consumables beyond a slide and a drop of oil.

What Does Hair Root Morphology Tell You?

Canine hair cycles through three phases, and the root shape at the plucked end reports which phase that follicle was in when the hair was removed. Reading the ratio between phases is where a trichogram becomes a diagnostic tool rather than a curiosity.

Anagen roots are the growing phase. They appear rounded, glossy, soft, and often bent or curved at the base, with pigment extending fully to the root and a visible root sheath. Telogen roots are the resting phase. They appear straight, uniform, and club-shaped or spear-shaped, with a rough, non-pigmented, keratinized bulb. Catagen roots are the brief transitional phase and are rarely counted clinically.

A healthy dog in a normal coat cycle shows a mixture, with the exact ratio varying by breed, season, and body site. What raises concern is a coat that is 100 percent telogen. Complete follicular arrest, with no anagen hairs present at all, is a hallmark of endocrine and follicular dysplastic disease. Hypothyroidism, hyperadrenocorticism, growth hormone responsive dermatosis, sex hormone imbalances, and post-clipping alopecia all drive follicles into prolonged telogen. If a trichogram from a dog with symmetrical truncal hair loss shows exclusively telogen bulbs, endocrine testing moves to the top of the list rather than the bottom.

The reverse pattern also carries meaning. An unusually high anagen proportion in a dog receiving chemotherapy or after a severe systemic illness can indicate anagen effluvium, where hair shafts fracture at the level of the follicle during active growth, producing sudden diffuse loss within days to weeks. For a broader look at the endocrine causes behind these patterns, see Understanding Hormonal Hair Loss Patterns in Dogs.

How Do Veterinarians Perform a Trichogram?

The procedure is short, but technique determines whether the result is interpretable. Roots tear away when hairs are yanked at the wrong angle, and a slide full of broken bulbs answers nothing.

The clinician selects the border between affected and normal-appearing skin, since the active edge of a lesion yields more information than the bald center. Using hemostats or forceps with the tips padded, often with rubber tubing to prevent crushing, the operator grasps 20 to 50 hairs close to the skin and pulls firmly in the direction of hair growth, in one smooth motion. Hairs are laid on a slide in parallel alignment, covered with mineral oil, and coverslipped.

Reading proceeds systematically. Low power first, scanning the full length of the shafts for fractures, casts, and pigment clumping. Then the root ends, counted and classified as anagen or telogen. Then high power for Demodex mites, dermatophyte arthrospores, and ectothrix invasion. Multiple sites are sampled when lesions differ in appearance.

Trichograms are frequently paired with other chairside tests, because each covers a gap the others leave. Acetate tape preparation captures surface organisms that plucking misses, and dermatophyte test medium culture confirms fungal species that a trichogram can only suggest. Owners trying to work out which category of skin problem they are dealing with before a visit can start with the Dog Skin Condition Checker.

Signs and Findings to Watch For

Certain trichogram findings are close to diagnostic on their own, while others narrow the differential list substantially. The table below summarizes the patterns most often encountered in canine dermatology practice.

What Happens After a Trichogram Points to Infection?

When a trichogram shows arthrospores, yeast, or follicular casts alongside greasy, malodorous skin, the finding usually reflects Malassezia pachydermatis overgrowth, bacterial folliculitis, or both layered onto a primary disease. Yeast is a normal commensal on canine skin, but populations expand dramatically when the barrier is damaged by allergy, moisture, or endocrine disease, and counts above 10 organisms per high power field on cytology are widely used as a threshold for clinically relevant overgrowth.

Topical antimicrobial therapy is the backbone of management here, and veterinary dermatology consensus guidelines increasingly favor topicals over systemic drugs where lesions are accessible, both to limit antimicrobial resistance and to act directly at the follicular opening where organisms concentrate.

Yeast Dermatitis Spray contains ketoconazole and chlorhexidine. Ketoconazole is an azole antifungal that inhibits lanosterol 14 alpha demethylase, the enzyme fungi require to build ergosterol for their cell membranes, and without intact ergosterol the membrane becomes leaky and the organism cannot maintain itself. Chlorhexidine works by a separate mechanism, disrupting bacterial and yeast cell membranes through electrostatic binding, which is why the combination covers the mixed bacterial and fungal populations so often found together in follicular disease. It is an FDA-registered over the counter veterinary drug listed on DailyMed, not a cosmetic grooming product.

Spot treatment suits localized lesions such as paws, ventral neck, and skin folds, where a spray reaches the site without bathing the entire dog. For diffuse involvement, medicated bathing remains the more thorough approach. Background on the organism itself is covered in Yeast Infections in Dogs, and dogs whose hair loss turns out to be immune-mediated rather than infectious are discussed in Alopecia Areata in Dogs.

Limitations and When to Move Beyond the Trichogram

A trichogram is a screening test, not a final answer, and treating it as definitive causes real diagnostic errors. Its most important limitation is that a negative result never rules disease out. Plucking samples only the hairs that release, and lesional distribution is patchy, so a dog with genuine demodicosis can yield a clean slide from an unlucky site.

Sensitivity varies sharply by body region. Hairs from the interdigital spaces and periocular skin yield mites more reliably than trunk samples, which is why trichograms are often preferred over deep scraping for feet and faces, where scraping is painful and technically awkward. On the trunk, deep skin scraping remains the more sensitive test for Demodex.

Dermatophyte identification is likewise presumptive. Arthrospores visible on a shaft confirm fungal invasion but do not identify the species, and species matters for prognosis, zoonotic risk, and treatment length. Culture or PCR is required. Wood's lamp examination can support the suspicion, though only about half of Microsporum canis strains fluoresce, so a dark lamp proves nothing either.

Cases that stay unresolved after trichogram, cytology, scraping, and culture generally warrant skin biopsy, which remains the reference standard for follicular dysplasias, sebaceous adenitis, and immune-mediated disease. Biopsy is the point at which follicular architecture, not just the hair that came out of it, becomes visible.

Prevention and Long-Term Coat Monitoring

Trichograms are not only a diagnostic tool. Repeated over time, they are one of the cheapest ways to track whether a treatment plan is actually restoring follicular function.

In a dog being treated for hypothyroidism, a follow-up trichogram at eight to twelve weeks that shows anagen roots reappearing confirms the follicles have restarted, often well before the owner notices visible regrowth. In demodicosis, sequential negative trichograms are part of the standard criteria for declaring cure, with most protocols requiring two consecutive negative samples one month apart before therapy stops.

Owners can support this at home with simple habits. Regular grooming with a brush appropriate to the coat type redistributes sebum and removes shed telogen hair before it mats. Photographing affected areas monthly under the same lighting creates an objective record that is far more useful at recheck than recalled impressions. Keeping folds, feet, and pressure points dry limits the moisture that drives microbial overgrowth in the first place.

Most importantly, alopecia that appears suddenly, spreads, or comes with systemic signs such as weight change, lethargy, excessive thirst, or heat-seeking behavior is not a grooming problem and should not be managed at home. Those combinations point toward endocrine disease, and every week of delay is another cycle of follicles arresting.

Frequently Asked Questions

Does a trichogram hurt my dog?

Plucking 20 to 50 hairs causes brief, mild discomfort similar to removing a splinter, and most dogs tolerate it without sedation. It is considerably less painful than deep skin scraping, which is why trichograms are often preferred for sensitive areas such as the face and between the toes.

How much does a trichogram cost?

A trichogram is one of the least expensive tests in veterinary dermatology, typically bundled into an exam or charged as a minor in-house lab fee. The materials cost only pennies since the test needs forceps, a slide, mineral oil, and a coverslip, and results are available within minutes rather than days.

Can a trichogram diagnose ringworm in dogs?

A trichogram can show fungal arthrospores coating and invading the hair shaft, which strongly supports dermatophytosis, but it cannot identify the species. Confirmation requires fungal culture on dermatophyte test medium or PCR, and species identification matters because it changes treatment length and zoonotic risk to the household.

What does it mean if all my dog's hairs are in telogen?

A coat that is entirely telogen means every sampled follicle has stopped growing hair and is sitting in the resting phase. In a dog with symmetrical, non-itchy hair loss this pattern points toward hypothyroidism, hyperadrenocorticism, sex hormone imbalance, or post-clipping alopecia, and it justifies moving directly to endocrine bloodwork.

Can I tell if my dog is licking off her fur without a microscope?

Sometimes, but not reliably. Many dogs groom compulsively when unobserved, and owners genuinely believe the hair is falling out on its own. The blunt, splintered tips seen on a trichogram are the objective evidence, and they redirect the workup toward allergies, parasites, or pain rather than a hormonal cause.

Sources

1. Beco L, Fontaine J, Bergvall K, Favrot C. Comparison of skin scrapes and hair plucks for detecting Demodex mites in canine demodicosis. Veterinary Dermatology. 2007;18(5):381.
2. Miller WH, Griffin CE, Campbell KL. Muller and Kirk's Small Animal Dermatology, 7th ed. Elsevier. 2013:57-107.
3. Saridomichelakis MN, Koutinas AF, Farmaki R, et al. Relative sensitivity of hair pluckings and exudate microscopy for the diagnosis of canine demodicosis. Veterinary Dermatology. 2007;18(2):138-141.
4. Kim HJ, Kang MH, Kim JW, Kim DH, Park HM. Restoration of hair coat in a dog with color dilution alopecia. Journal of Veterinary Clinics. 2011;28(4):426-429.
5. Moriello KA, Coyner K, Paterson S, Mignon B. Diagnosis and treatment of dermatophytosis in dogs and cats: Clinical Consensus Guidelines of the World Association for Veterinary Dermatology. Veterinary Dermatology. 2017;28(3):266-268.

Related Reading

• Acetate Tape Preparation for Dog Skin: A Quick Diagnostic Technique
• Understanding Hormonal Hair Loss Patterns in Dogs: Which Hormone Is the Cause
• Dermatophyte Test Medium (DTM) Culture for Dogs: How Fungal Cultures Work
• Alopecia Areata in Dogs: Immune-Mediated Patchy Hair Loss

Emiel Maddens

Founder of Vetified. Develops topical antifungal and antimicrobial formulations for companion animals. Vetified products are listed on DailyMed and manufactured through FDA-registered facilities in the United States.

Veterinary review: All Vetified content is developed in consultation with licensed veterinary professionals and references peer-reviewed research published in journals including Veterinary Dermatology, JAVMA, and Journal of Small Animal Practice.