Skin Infections

Folliculitis in Dogs: Bacterial and Fungal Hair Follicle Infections

By Emiel Maddens · Reviewed in consultation with licensed veterinary professionals · Updated June 2026 · 10 min read

Folliculitis in Dogs guide for dog owners

Key Takeaways

Folliculitis is inflammation of hair follicles caused by bacteria, fungi, or parasites, and it is one of the most common skin conditions in dogs.
Superficial folliculitis affects the upper portion of the follicle, while deep folliculitis extends into surrounding tissue and carries a higher risk of scarring.
Staphylococcus pseudintermedius is the most frequent bacterial cause, while dermatophytes (ringworm fungi) drive most fungal cases.
Diagnosis typically involves skin cytology, bacterial culture, fungal culture, and sometimes biopsy to identify the underlying trigger.
Successful long-term management requires treating the infection and addressing predisposing factors such as allergies, endocrine disease, or immune suppression.

Folliculitis, the inflammation of one or more hair follicles, ranks among the most frequently diagnosed dermatologic conditions in veterinary practice. The condition can present as small red bumps, pustules, crusted papules, or areas of hair loss scattered across the trunk, abdomen, or groin. While folliculitis itself is often straightforward to recognize on physical examination, the underlying cause can be complex and multifactorial. Dogs of any age, breed, or coat type can develop folliculitis, although certain breeds carry a genetic predisposition that makes recurrence more likely without careful ongoing management.

The hair follicle serves as a protective sheath for the growing hair shaft, and it also houses sebaceous glands, arrector pili muscles, and a rich network of blood vessels. When bacteria, fungi, or parasites breach the follicular wall, the immune system mounts an inflammatory response that produces the characteristic signs of redness, swelling, and pustule formation. In superficial cases the inflammation remains confined to the upper follicle, and the condition often resolves with appropriate topical therapy. Deep folliculitis, however, extends beyond the follicular wall into the surrounding dermis, creating painful nodules, draining tracts, and a risk of permanent scarring that demands more aggressive treatment.

Understanding the distinction between bacterial and fungal folliculitis is critical because the treatment protocols differ substantially. Bacterial folliculitis typically responds to targeted antibiotics guided by culture and sensitivity testing, combined with topical antimicrobial therapy. Fungal folliculitis requires antifungal medications and environmental decontamination to prevent reinfection. In many cases, folliculitis is secondary to an underlying condition such as atopic dermatitis, food allergy, hypothyroidism, or Cushing's disease. Identifying and managing these root causes is essential for preventing frustrating cycles of recurrence that diminish a dog's quality of life and increase treatment costs over time.

What Is Folliculitis and How Does It Develop

Anatomy of the Hair Follicle

The canine hair follicle is a complex structure that extends from the skin surface deep into the dermis. Each follicle contains the hair bulb where active growth occurs, the inner and outer root sheaths that guide hair development, and associated sebaceous glands that produce protective oils. In compound follicles, which are the norm in most dog breeds, multiple hair shafts emerge from a single follicular opening. This anatomical arrangement means that infection of one follicle can quickly spread to adjacent structures, producing clusters of lesions that enlarge over days to weeks.

How Infection Establishes

Folliculitis develops when the normal defensive barriers of the follicle are compromised. The skin surface is populated by a diverse community of commensal bacteria and fungi that ordinarily coexist without causing disease. When factors such as excessive moisture, friction, trauma, immune suppression, or allergic inflammation disrupt follicular integrity, opportunistic organisms gain access to deeper tissues. The immune response to this invasion produces neutrophil infiltration, edema, and eventually the formation of pustules filled with white blood cells, bacteria, and cellular debris.

Superficial Versus Deep Folliculitis

Superficial folliculitis is confined to the infundibulum, the uppermost portion of the follicle above the sebaceous duct opening. Clinically it appears as small papules, pustules, and epidermal collarettes, which are circular rings of peeling skin that mark the edges of ruptured pustules. Deep folliculitis occurs when infection extends below the sebaceous duct into the isthmus and bulb regions. This deeper infection produces larger, more painful nodules, furunculosis where the follicle ruptures and releases its contents into the dermis, and draining tracts that discharge purulent material. Deep folliculitis is considerably harder to treat and carries a higher risk of permanent scarring and pigmentation changes.

Bacterial Folliculitis: Causes and Clinical Signs

Staphylococcus pseudintermedius as Primary Pathogen

Staphylococcus pseudintermedius is the bacterial species most commonly isolated from canine folliculitis cases, accounting for the vast majority of bacterial skin infections in dogs. This organism is a normal commensal of canine skin and mucous membranes, residing particularly in the nasal passages, perineum, and between the toes. Under normal circumstances, the dog's immune system and intact skin barrier keep S. pseudintermedius populations in check. When these defenses are weakened by allergic disease, hormonal imbalance, or immune suppression, the bacterium proliferates and invades follicular structures. Methicillin-resistant strains (MRSP) have become an increasing clinical concern, making culture and sensitivity testing essential for guiding effective antibiotic therapy.

Clinical Presentation of Bacterial Folliculitis

Bacterial folliculitis in dogs typically presents with papules, pustules, and crusted lesions distributed across the ventral abdomen, groin, axillae, and trunk. In short-coated breeds, the lesions often appear as small raised bumps that give the coat a moth-eaten appearance. In long-coated breeds, the condition may be harder to detect visually, and owners may first notice excessive shedding, dull coat quality, or a musty odor. As pustules rupture, they leave behind epidermal collarettes and areas of hyperpigmentation that can persist for weeks after the infection has resolved.

Breed Predisposition to Bacterial Folliculitis

Several breeds demonstrate a heightened susceptibility to bacterial folliculitis due to coat characteristics, skin fold anatomy, or genetic immune factors. Short-coated breeds such as Bulldogs, Boxers, Doberman Pinschers, and Dalmatians are particularly prone to superficial bacterial folliculitis. German Shepherds have a well-documented predisposition to deep bacterial folliculitis and furunculosis, especially in the perianal region. Shar-Peis carry multiple genetic risk factors, including excessive skin folding and mucinosis, that create an environment conducive to recurrent bacterial infection.

Fungal Folliculitis: Dermatophytes and Beyond

Dermatophyte Infections of Hair Follicles

Dermatophytosis, commonly known as ringworm, occurs when fungi of the genera Microsporum or Trichophyton invade the hair shaft and follicle. Microsporum canis is the most frequently identified dermatophyte in dogs, although Trichophyton mentagrophytes and Microsporum gypseum are also encountered. These organisms produce keratinases, enzymes that digest keratin protein, allowing them to colonize the hair shaft and follicular wall. The resulting infection produces circular patches of alopecia with broken hair stubs, scaling, and sometimes a grayish crust. Unlike bacterial folliculitis, dermatophyte infections are zoonotic, meaning they can spread from dogs to humans and other animals in the household.

Malassezia and Other Fungal Contributors

While dermatophytes invade the hair shaft itself, Malassezia pachydermatis is a yeast organism that typically colonizes the skin surface and can secondarily contribute to follicular inflammation. Malassezia overgrowth is most commonly associated with underlying allergic disease or seborrhea, and it produces a characteristic greasy texture and musty odor. In some cases, Malassezia folliculitis can develop in dogs with severely compromised skin barriers, particularly in breeds like West Highland White Terriers, Basset Hounds, and Cocker Spaniels that are genetically predisposed to Malassezia dermatitis.

Diagnosing Fungal Folliculitis

Fungal folliculitis requires specific diagnostic approaches that differ from bacterial workups. Wood's lamp examination can detect approximately 50% of Microsporum canis infections, which fluoresce apple-green under ultraviolet light. However, a negative Wood's lamp result does not rule out dermatophytosis, as many species and strains do not fluoresce. Fungal culture using dermatophyte test medium (DTM) or Sabouraud dextrose agar remains the gold standard for definitive diagnosis, although results may take 10 to 21 days. PCR testing for dermatophyte DNA offers faster turnaround but is not universally available. Trichography, the microscopic examination of plucked hairs, can reveal fungal arthrospores surrounding or within the hair shaft and provides immediate diagnostic information.

Diagnostic Approach to Folliculitis

Skin Cytology and Its Role

Impression cytology is typically the first diagnostic step when folliculitis is suspected. The veterinarian collects samples by pressing a glass slide directly onto intact pustules, using clear adhesive tape to lift surface organisms, or making impression smears from ruptured lesions. After staining with modified Wright-Giemsa stain (Diff-Quik), the slide is examined under the microscope for the presence of bacteria, yeast organisms, and inflammatory cells. Finding intracellular cocci, bacteria that have been engulfed by neutrophils, confirms active bacterial infection rather than mere surface contamination. Cytology also helps differentiate bacterial from fungal causes and can identify mixed infections that require combination therapy.

Bacterial Culture and Sensitivity Testing

While cytology provides rapid preliminary information, bacterial culture with antimicrobial sensitivity testing is essential for guiding appropriate antibiotic selection, particularly in cases of deep folliculitis, recurrent infections, or suspected methicillin-resistant organisms. Samples are ideally collected from intact pustules using sterile technique to avoid contamination with surface commensals. The laboratory identifies the bacterial species and tests its susceptibility to a panel of antibiotics, allowing the veterinarian to select the most effective agent while minimizing the risk of promoting further resistance development.

Skin Biopsy and Histopathology

In cases where folliculitis is atypical in appearance, fails to respond to empirical therapy, or is suspected to have an unusual underlying cause, skin biopsy provides definitive diagnostic information. Punch biopsies of 6 to 8 millimeters in diameter are collected from representative lesions under local anesthesia. Histopathological examination reveals the pattern and depth of inflammation, identifies the types of inflammatory cells present, and can detect organisms within the follicular wall that were not apparent on cytology. Special stains such as PAS (periodic acid-Schiff) and GMS (Grocott's methenamine silver) highlight fungal elements, while tissue Gram staining identifies bacterial organisms within the tissue sections.

Treatment Protocols for Bacterial Folliculitis

Topical Antimicrobial Therapy

Topical therapy plays a central role in managing superficial bacterial folliculitis and serves as an important adjunct to systemic antibiotics in deep infections. Chlorhexidine-based products at concentrations of 2% to 4% are among the most widely recommended topical antimicrobials for canine folliculitis, as they provide broad-spectrum activity against Staphylococcus species with minimal risk of resistance development. Medicated shampoos containing chlorhexidine, benzoyl peroxide, or ethyl lactate help remove surface bacteria, crusts, and debris while delivering antimicrobial agents directly to the affected follicles. Topical sprays and mousses offer a convenient alternative for localized lesions or for dogs that do not tolerate frequent bathing.

Systemic Antibiotic Therapy

Systemic antibiotics are indicated for deep bacterial folliculitis, widespread superficial folliculitis, and cases that have failed to respond to topical therapy alone. Antibiotic selection should ideally be guided by culture and sensitivity results, especially given the increasing prevalence of methicillin-resistant staphylococcal infections. First-line empirical choices typically include cephalexin, amoxicillin-clavulanate, or clindamycin, with treatment duration of at least 21 days for superficial infections and 6 to 8 weeks for deep folliculitis. A critical principle in veterinary dermatology is to continue antibiotic therapy for at least 7 to 14 days beyond clinical resolution to ensure complete elimination of the infection and reduce the risk of relapse.

Managing Methicillin-Resistant Infections

Methicillin-resistant Staphylococcus pseudintermedius (MRSP) infections present significant treatment challenges because these organisms are resistant to all beta-lactam antibiotics, which constitute the most commonly prescribed class for canine skin infections. Treatment of MRSP folliculitis relies heavily on topical antimicrobial therapy as the primary approach, with systemic antibiotics reserved for deep or extensive infections based on culture-guided selection from a limited pool of effective agents. Chlorhexidine-based topical products remain effective against MRSP strains because the mechanism of chlorhexidine action differs fundamentally from that of beta-lactam antibiotics, making cross-resistance extremely rare.

Treatment Protocols for Fungal Folliculitis

Systemic Antifungal Medications

Treatment of dermatophyte folliculitis requires systemic antifungal therapy because topical agents alone cannot adequately penetrate the hair shaft where the fungal organisms reside. Itraconazole and terbinafine are the most commonly prescribed systemic antifungals for canine dermatophytosis, with treatment typically continuing for a minimum of 6 to 8 weeks. Some dermatologists recommend pulse therapy protocols where the medication is administered for one week followed by one week off, as antifungal drugs accumulate in keratinized tissues and maintain therapeutic concentrations during the off-treatment periods. Treatment should continue until two consecutive negative fungal cultures performed at two-week intervals confirm mycological cure.

Topical Antifungal Therapy as Adjunct

While systemic antifungals address the established infection within the hair shaft, topical antifungal therapy serves the important role of reducing environmental contamination and limiting the spread of infective arthrospores. Lime sulfur dips, miconazole-chlorhexidine shampoos, and enilconazole rinses are commonly used adjunctive topical treatments. Topical therapy should be applied at least twice weekly and extended to the entire body rather than limited to visible lesions, as dermatophyte spores can be present on clinically normal skin. This whole-body approach helps reduce the environmental fungal burden and protects other animals and humans in the household from exposure.

Environmental Decontamination

Dermatophyte spores can survive in the environment for months to years, making environmental decontamination an essential component of treatment. Contaminated bedding, grooming tools, collars, and toys should be either discarded or thoroughly disinfected with a solution of 1:10 household bleach. Carpets and upholstered furniture should be vacuumed frequently, with the vacuum bag discarded after each use. Hard surfaces can be cleaned with accelerated hydrogen peroxide or dilute bleach solutions. Environmental decontamination should continue throughout the treatment period and for at least two weeks after the patient achieves mycological cure to prevent reinfection from residual spores.

Addressing Underlying Causes and Preventing Recurrence

Allergic Disease as a Predisposing Factor

Allergic dermatitis, including atopic dermatitis, food allergy, and flea allergy dermatitis, is the most common underlying cause of recurrent bacterial folliculitis in dogs. Allergic inflammation disrupts the normal skin barrier, alters the cutaneous microbiome, and impairs local immune defenses, creating conditions that favor bacterial overgrowth and follicular invasion. Dogs with recurrent folliculitis should undergo a thorough allergy workup that may include elimination diet trials, intradermal allergy testing, or serum allergy panels. Effective management of the underlying allergic condition through allergen avoidance, immunotherapy, or immunomodulatory medications is essential for breaking the cycle of recurrent infection.

Endocrine Disease and Immune Suppression

Hypothyroidism and hyperadrenocorticism (Cushing's disease) are two endocrine conditions that significantly increase susceptibility to folliculitis. Hypothyroidism reduces skin cell turnover, diminishes sebum production, and impairs local immune function, while Cushing's disease produces chronically elevated cortisol levels that suppress both cellular and humoral immunity. Dogs with recurrent or treatment-resistant folliculitis, particularly those in middle to older age, should have thyroid function and adrenal gland function evaluated through appropriate blood tests. Correcting the underlying endocrine imbalance often leads to dramatic improvement in skin health and a marked reduction in infection frequency.

Long-Term Maintenance Strategies

Preventing folliculitis recurrence in predisposed dogs requires a proactive maintenance approach that combines regular topical antimicrobial therapy with management of identified underlying conditions. Weekly to biweekly bathing with antimicrobial shampoos helps maintain a healthy skin surface and reduces colonization by pathogenic organisms. Regular skin checks by the owner allow early detection of new lesions before they progress to widespread infection. Dietary supplementation with omega-3 fatty acids supports skin barrier function and modulates the inflammatory response. Owners should also minimize environmental risk factors such as excessive humidity, contact with infected animals, and mechanical trauma from rough play surfaces.

When to See Your Veterinarian

While mild, localized folliculitis may respond to topical antimicrobial therapy at home, several situations warrant prompt veterinary evaluation. Any folliculitis that produces deep, painful nodules, draining tracts, or bleeding lesions should be examined by a veterinarian, as these signs indicate deep infection that typically requires systemic antibiotic or antifungal therapy. Folliculitis that spreads rapidly despite topical treatment, recurs within weeks of apparent resolution, or is accompanied by systemic signs such as lethargy, decreased appetite, or fever also demands professional assessment.

Puppies and senior dogs with folliculitis deserve particular attention because their immune systems may be less equipped to fight infection effectively. Dogs receiving immunosuppressive medications for other conditions, such as corticosteroids or cyclosporine for autoimmune disease, are at heightened risk for severe folliculitis and should be monitored closely for any skin changes. If you notice circular patches of hair loss, especially with broken hair stubs or scaling, prompt veterinary evaluation is important to rule out dermatophytosis and implement appropriate treatment and household precautions to prevent zoonotic transmission.

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Folliculitis in Dogs FAQ

Q: Is folliculitis in dogs contagious to other pets or humans?

Bacterial folliculitis caused by Staphylococcus pseudintermedius is generally species-specific and poses minimal risk to humans or other pet species. However, fungal folliculitis caused by dermatophytes such as Microsporum canis is highly contagious and can spread to other dogs, cats, and humans through direct contact or contaminated environments. If dermatophytosis is diagnosed, all animals in the household should be evaluated and the environment should be thoroughly decontaminated.

Q: How long does it take for folliculitis to resolve with treatment?

Superficial bacterial folliculitis typically shows visible improvement within 7 to 14 days of appropriate treatment and resolves fully within 3 to 4 weeks. Deep bacterial folliculitis may require 6 to 12 weeks of systemic antibiotic therapy. Fungal folliculitis often takes 6 to 12 weeks to achieve mycological cure, confirmed by negative fungal cultures. Residual changes such as hyperpigmentation and mild hair loss may persist for several months after the infection has cleared.

Q: Can I use over-the-counter products to treat my dog's folliculitis at home?

Mild, localized folliculitis may benefit from topical antimicrobial products such as chlorhexidine sprays or wipes as a supportive measure. However, self-treating without a proper diagnosis carries risks, as the wrong treatment can worsen certain types of folliculitis or mask an underlying condition that needs specific therapy. Veterinary diagnosis is recommended to identify the causative organism and any predisposing factors before initiating treatment.

Q: Why does my dog keep getting folliculitis even after treatment?

Recurrent folliculitis almost always indicates an unresolved underlying condition. The most common culprits are allergic dermatitis (atopic, food, or flea allergy), endocrine diseases like hypothyroidism or Cushing's disease, and immune system disorders. Each episode of folliculitis should prompt investigation into these predisposing factors. Successful long-term control requires treating both the infection and the underlying cause simultaneously.

Q: What breeds are most prone to folliculitis?

Short-coated breeds such as Bulldogs, Boxers, Doberman Pinschers, Dalmatians, and Pit Bull Terriers are particularly susceptible to superficial bacterial folliculitis due to their coat structure and skin characteristics. German Shepherds have a well-known predisposition to deep folliculitis and furunculosis. Shar-Peis are prone to recurrent folliculitis due to their skin fold anatomy and genetic factors. West Highland White Terriers, Basset Hounds, and Cocker Spaniels are predisposed to Malassezia-associated folliculitis.

Sources

Miller, W.H., Griffin, C.E., Campbell, K.L. (2013). Muller & Kirk's Small Animal Dermatology, 7th Edition. Elsevier. Chapters on bacterial and fungal skin diseases.

Hillier, A., et al. (2014). Guidelines for the diagnosis and antimicrobial therapy of canine superficial bacterial folliculitis. Veterinary Dermatology, 25(3), 163-e43.

Moriello, K.A., Coyner, K., Paterson, S., Mignon, B. (2017). Diagnosis and treatment of dermatophytosis in dogs and cats. Veterinary Dermatology, 28(3), 266-e68.

Morris, D.O., et al. (2017). Potential for pet animals to harbour methicillin-resistant Staphylococcus aureus when living with human MRSA patients. Journal of Antimicrobial Chemotherapy, 67(1), 116-118.

Bajwa, J. (2016). Canine Malassezia dermatitis. Canadian Veterinary Journal, 57(10), 1065-1067.

Bloom, P. (2014). Canine superficial bacterial folliculitis: current understanding of its etiology, diagnosis, and treatment. The Veterinary Journal, 199(2), 217-222.