In an era dominated by molecular diagnostics, advanced imaging and the rise of AI, it’s easy to overlook the humble skin scrape. Yet this simple procedure remains the diagnostic cornerstone for some of the most common parasitic skin diseases in veterinary practice. When performed correctly, it is rapid, inexpensive and immediately informative. However, poor technique or incorrect interpretation risks false-negative results that can delay diagnosis.

The diagnostic value of skin scrapes depends on how and where the sample is collected. Studies comparing deep skin scrapings with hair plucks, tape preparations and other sampling methods for demodicosis, and evaluations of conventional skin scrapings for sarcoptic mange, consistently show that suboptimal sampling technique is a major contributor to diagnostic failure. Understanding the biological behaviour of different mites – and adapting technique accordingly – is therefore essential.

This article focuses on the practical “art” of skin scraping, why this is important for detecting Demodex mites, and why even with excellent technique, skin scrapes may still fail to identify Sarcoptes scabiei.

Figure 1. Sarcoptes scabiei, skin. Epidermis with moderate to marked acanthosis and orthokeratotic and parakeratotic hyperkeratosis. Multiple adult mites are present within the superficial stratum corneum and epidermis. Haematoxylin and eosin (H&E).

Why mite biology dictates technique

Before considering skin scrape technique, it is important to understand how Demodex and Sarcoptes differ in their biology and behaviour. These differences largely explain why skin scraping can be highly rewarding in one disease and frustratingly unrewarding in the other.

Demodex: a follicular commensal

Demodicosis is a common parasitic skin disease in dogs. Reported prevalence varies widely, ranging from approximately 0.4% to 23% in epidemiological studies, depending on population and diagnostic criteria.¹ Three Demodex species are recognised as normal commensals of canine skin: Demodex canis, Demodex cornei and Demodex injai. All inhabit hair follicles and/or sebaceous glands, but when mites multiply in excessive numbers clinical disease may be seen. D canis is most commonly associated with generalised demodicosis, with D injai also implicated in some cases.

Demodicosis is commonly classified according to age of onset and extent of disease. Localised disease typically occurs in dogs under one year of age and often resolves spontaneously. Generalised demodicosis usually presents before 18 months of age, whereas adult-onset disease (after 1.5 years) is more often associated with underlying immunosuppression or concurrent disease.

The pathophysiology of demodicosis is not fully understood. Current evidence suggests that a temporary or inherited defect in cell-mediated immunity, particularly involving T-cell function, plays an important role in juvenile-onset disease.² In adult dogs, immunosuppressive conditions are frequently implicated, although other, as yet unidentified, factors may also contribute. It is also important to bear in mind that Demodex mites are part of the normal cutaneous microfauna, meaning that interpretation of diagnostic findings must always be made in the context of clinical signs.

Sarcoptes

Unlike Demodex, Sarcoptes scabiei var. canis is a true pathogen with no commensal phase. These highly contagious mites are transmitted by direct contact with infected dogs or, less commonly, through contact with fox carcasses or contaminated environments. The disease is zoonotic, though human lesions are typically self-limiting once the canine source is treated.

The lifecycle and pathogenesis of Sarcoptes help explain why it can be so diagnostically challenging. Males and females mate on the skin surface, after which the female burrows into the upper layers of the epidermis, creating winding tunnels as she feeds on tissue fluid and cellular debris. Within these tunnels, eggs are deposited over a period of several months. The complete lifecycle from egg to adult takes two to three weeks.3

Clinical signs are dominated by intense pruritus, largely attributable to a hypersensitivity reaction to mite antigens rather than to mite burden per se. This explains why even small numbers of mites can trigger severe clinical disease, and conversely, why finding mites on skin scrapes can be extraordinarily difficult. The most commonly affected sites include the ear pinnae, elbows, hocks and ventral abdomen. The pinnal-pedal reflex – a scratch response elicited by rubbing the ear margin – is positive in approximately 90% of cases and remains one of the most useful clinical diagnostic indicators.³

Figure 2. Sarcoptes scabiei, skin. Adult mite measuring approximately 135 × 115 µm with a approximately 2 µm chitinous exoskeleton, dorsal spines, jointed appendages, striated musculature, and body cavity (hemocoel). H&E.

Biological differences with diagnostic consequences

Table 1 summarises the fundamental differences between these two parasitic diseases and their implications for diagnosis and management. The location of each mite within the skin is perhaps the most important factor determining diagnostic approach. Demodex inhabits hair follicles and rarely sebaceous glands deep within the dermis. These structures run perpendicular to the skin surface, creating anatomical “silos” that protect mites from superficial sampling. Sarcoptes, by contrast, burrows within the epidermis itself, creating horizontal tunnels just beneath the stratum corneum. However, these tunnels are often covered by crusts and scales, and the female mite spends much of her time within the tunnel rather than on the surface.

Table 1. Superficial versus deep dwelling mites.⁴

	Sarcoptes species	Demodex species
Disease	Sarcoptic mange (scabies)	Demodicosis
Location in skin	Superficial epidermis (burrows within stratum corneum)	Hair follicles, sebaceous glands
Best scraping approach	Superficial, broad sampling of multiple sites	Deep, focal scraping with skin squeezing
Commensal	No	Yes
Hypersensitivity-driven signs	Yes	No
Ease of finding mites on scrape	Often difficult (low sensitivity)	Usually straightforward with good technique
Typical treatment course	Often short and uncomplicated	May be prolonged; relapse possible

The commensal status of Demodex has important interpretive implications. Finding one or two mites may simply reflect normal colonisation, whereas finding multiple mites – or mites in association with appropriate clinical signs – indicates pathological overgrowth. For Sarcoptes, any mite identified is diagnostically significant, though their scarcity means that negative scrapes are common even in confirmed cases.

The hypersensitivity component of sarcoptic mange means that clinical signs can be markedly disproportionate to mite numbers. A type IV hypersensitivity reaction typically develops around two to five weeks after initial infestation, resulting in intense pruritus that persists even when mite burdens are low. Demodicosis, in contrast, is largely a consequence of mite burden rather than a hypersensitivity reaction, meaning that clinical signs generally correlate with mite numbers.

In terms of treatment, the two conditions also differ. Sarcoptes is usually readily treated by modern acaricides, whereas demodicosis – particularly generalised forms – often requires a prolonged treatment course and may relapse if underlying predisposing factors are not addressed.

Figure 3. Demodex canis, skin. Multiple intrafollicular sections of mites. The epidermis shows mild to moderate hyperplasia with parakeratotic hyperkeratosis. The dermis contains mild to moderate lymphoplasmacytic inflammation. H&E.

The art of the skin scrape

Deep skin scrapings remain the diagnostic gold standard for demodicosis. With good technique, reported sensitivities are usually higher than other methods, although tape squeeze preparations can sometimes be useful.2,5 With skin scrapes, the key to success lies in understanding the mite’s location and squeezing the skin to physically bring mites from the depths of hair follicles to the scraped surface.

Site selection. Diagnostic yield is highest when sampling from active primary lesions. Follicular papules and pustules are ideal targets, as these represent sites of active mite proliferation and follicular inflammation. Areas immediately adjacent to papules, areas of crusting or obvious hair loss also tend to be productive.

In medium- or long-haired breeds, clipping an area of skin before scraping, removes physical obstruction and allows better visualisation of the skin surface and any surface changes that might guide ideal sampling locations. Where crusting or scaling is present, avoid displacing this material during clipping, as it should be included in the sample.

Equipment and preparation. The equipment required is minimal: a No. 10 scalpel blade, mineral oil, glass slides and coverslips. Place a drop of mineral oil on the blade before scraping – this aids adherence of scraped material to the blade during collection.

Squeezing and stretching. Before, and sometimes during scraping, firmly squeeze or pinch the skin between thumb and forefinger. Squeezing mechanically expresses Demodex mites from the depths of hair follicles toward the skin surface, dramatically increasing the number of mites available for collection and increasing the likelihood of an accurate diagnosis.

Stretching the skin taut makes skin scrapes easier to perform but also serves an additional function. Hair follicles naturally lie at an angle to the skin surface. Stretching straightens these follicles, reducing the tortuous path that would otherwise shield mites. This is particularly important in areas where skin is mobile or naturally folded.

Depth and technique. Scrape firmly in the direction of hair growth until capillary bleeding occurs. This confirms that sufficient depth has been achieved to reach the hair follicles. The scraped area should be approximately 1cm², and multiple sites should be sampled. Five to six scrapes from different locations are usually recommended to maximise sensitivity, particularly when clinical suspicion is high but initial scrapes are negative.

Transfer the collected material to a glass slide with a drop of mineral oil, apply a coverslip, and examine under low magnification (x4 or x10 objective). Demodex mites are elongated and cigar-shaped, making them readily recognisable. Scan the entire sample systematically, as mites may be unevenly distributed. Examine samples promptly where possible as mite morphology may deteriorate over time, potentially affecting identification.

The diagnostic threshold is relatively straightforward: according to World Association for Veterinary Dermatology consensus guidelines, finding more than one Demodex mite on any given test is an indication of clinically relevant demodicosis.

All life stages may be observed, including adults, nymphs, larvae and eggs. The presence of numerous immature forms suggests active reproduction and further supports a diagnosis of demodicosis.

Figure 4. Demodex canis, skin. Multiple intrafollicular mites in longitudinal, transverse, and oblique sections. H&E.

The article continues beyond this point.

Read the full article: https://www.vettimes.com/clinical/small-animal/dermatology-diagnostics-the-art-of-the-skin-scrape

Original publication: Vet Times (19 May 2026), Volume 56, Issue 20, Pages 6-12

About the author

Karina Fresneda, DVM, DiplACVP, graduated from the National University of the Centre of Buenos Aires in 2000. She became a specialist in Anatomo-histopathological Veterinary Diagnosis after two years of training. For 15 years, she taught infectious diseases at the same university, while gaining clinical and laboratory experience in clinical pathology, cytology, and histopathology. She completed a 3-year residency in Anatomic Veterinary Pathology at the University of California, Davis. Karina also teaches courses on clinical pathology, cytology, and histopathology.

References

1. O’Neill, D.G., Turgoose, E., Church, D.B., Brodbelt, D.C., & Hendricks, A. (2020). Juvenile-onset and adult-onset demodicosis in dogs in the UK: prevalence and breed associations. The Journal of small animal practice, 61(1), 32–41. https://doi.org/10.1111/jsap.13067

2. Mueller, R.S., Rosenkrantz, W., Bensignor, E., Karaś-Tęcza, J., Paterson, T., Shipstone, M.A. (2020) Diagnosis and treatment of demodicosis in dogs and cats: Clinical consensus guidelines of the World Association for Veterinary Dermatology. Vet Dermatol. 31(1):5-27. doi: 10.1111/vde.12806

3. ESCCAP cgqtqpf1_0720_ESCCAP_GL3__English_v19_1p.pdf

4. Cerundolo, R. (2013), Diagnostic and therapeutic approach to common ectoparasitoses in small animal practice. In Practice, 35: 18-23. https://doi.org/10.1136/inp.f6661

5. Mueller, R.S. & Bettenay, S.V. (2017) Scraping, fine-needle aspiration and biopsy of skin and subcutaneous tissues. In: SJ Ettinger, EC Feldman, E Cote, eds. Textbook of veterinary internal medicine, 8th edition. St Louis, MO: Elsevier: 342–345.

6. Campbell, K., Scarff D. & Godfrey, D. (online) Skin: sarcoptic mange. In: Vetlexicon Canis. ISSN 2398-2942. Vetstream Ltd, UK.