Kerion: Comprehensive Guide To Diagnosis, Treatment & Prevention

A

kerion

is a localized, pus-filled inflammatory response to a dermatophyte fungal infection, most commonly manifesting on the scalp as

tinea capitis

. It appears as a boggy, tender abscess that can lead to temporary or permanent hair loss if untreated. While primarily affecting children, it may occur on the face (**tinea faciei**) or body (**tinea corporis**), often mistaken for bacterial abscesses or cellulitis.

What is kerion?

Kerion, also known as kerion celsi, represents an exaggerated immune reaction to fungal invasion by dermatophytes, forming a spongy, pus-exuding mass. This hypersensitivity leads to intense inflammation, pus formation, and follicular destruction, distinguishing it from standard ringworm infections. The lesion typically measures several centimeters, feels soft and boggy to palpation, and may ooze seropurulent material with crusting. Hairs in the affected area become loose (alopecia within kerion) and shed easily, creating bald patches. Regional lymphadenopathy is common, and systemic symptoms like fever, malaise, or nausea can occur in severe cases. A secondary id reaction, termed

dermatophytide

, may present as an itchy, eczematous rash elsewhere on the body.

Who gets kerion?

Kerion predominantly affects

children of primary school age

, particularly in urban settings where close contact facilitates spread. It is less frequent in adults unless immunocompromised (e.g., due to diabetes, HIV, or immunosuppressive therapy). Certain populations, such as those in tropical climates or with pet exposure, face higher risk. Girls and boys are equally affected, though cultural hair practices may influence presentation. Household outbreaks occur via shared combs, hats, or bedding, emphasizing its contagious nature.

Causes

Kerion arises from dermatophyte fungi invading keratin-rich structures like hair follicles. The immune system’s overzealous response causes the abscess-like swelling rather than the fungus alone. Key causative agents include:

• Microsporum canis: Zoonotic from cats/dogs, common in outbreaks; fluoresces green-yellow under Wood’s lamp.
• Trichophyton tonsurans: Anthropophilic (human-to-human), prevalent in urban areas; non-fluorescent.
• Trichophyton verrucosum: From cattle, rarer in humans.
• Microsporum audouinii: Historical cause, now less common.

Trichophyton rubrum rarely causes kerion despite being a common tinea corporis agent. Transmission occurs via direct contact with infected humans, animals, or fomites (e.g., combs, towels). Pets like kittens are frequent reservoirs for M. canis.

Clinical features

The hallmark is a

tender, boggy swelling

on the scalp, 3-10 cm in diameter, with pustules, crusting, and purulent discharge. Surrounding erythema and edema mimic bacterial impetigo or abscess. Key signs include:

• Localized

  alopecia

  with loose, broken hairs (“black dots” in endothrix infections).
• Tenderness and warmth.
• Posterior cervical

  lymphadenopathy

  .
• Possible

  fever, malaise

  , or id reaction (widespread itchy rash).

Inflammatory tinea corporis or faciei presents similarly but on non-hair-bearing skin. Pain arises from stretched skin and inflammation. Untreated, it progresses to scarring alopecia.

Diagnosis

Suspicion arises from the classic boggy appearance, especially with risk factors like animal contact or family infections. Confirmatory tests include:

Test	Description	Utility
Wood’s lamp	UV light; glows yellow-green for M. canis (negative in inflamed kerion)	Screening; limited sensitivity.
KOH microscopy	Skin/hair scrapings + 10-20% KOH; hyphae/spores visible in 24 hours	Rapid; dissolves keratinocytes.
Fungal culture	Sabouraud agar; identifies species in 2-4 weeks	Gold standard for speciation.
Bacterial swab	For secondary infection (common)	Guides antibiotics.

Biopsy is rarely needed but shows abscess with granulomatous inflammation and hyphae. Differential includes bacterial abscess, impetigo, tufted folliculitis, or neoplasm.

Management

Treatment requires

systemic antifungals

due to deep follicular penetration; topicals fail. Standard regimen:

• Oral griseofulvin (microsize 20-25 mg/kg/day; ultramicrosize half dose): 6-8 weeks minimum.
• Alternatives: Terbinafine (weight-based: 62.5-250 mg/day), itraconazole, or fluconazole.
• Steroids: Prednisone (1 mg/kg/day taper) for severe inflammation to prevent scarring.
• Antibiotics: If bacterial superinfection (e.g., cephalexin).
• Shampoos: Ketoconazole 2% or ciclopirox 1% twice weekly to reduce spores.

Monitor clinically; repeat cultures if no improvement in 4 weeks. Avoid incision/drainage, as it worsens scarring.

Prevention of spread

Kerion remains contagious for weeks despite treatment. Measures include:

• Disinfect/discard combs, brushes, hats, bedding.
• Daily antifungal shampoos for patient/household.
• Screen pets (vet fungal culture); treat if positive.
• No school until non-contagious (2 weeks treatment).
• Household screening for asymptomatic carriers.

Prognosis and hair regrowth

With prompt treatment, resolution occurs in 6-8 weeks, with hair regrowth in 90% of cases. Delay risks permanent scarring alopecia, especially if biopsied or incised. Early steroids mitigate fibrosis. Recurrence is rare with adherence.

Images

Clinical images depict boggy, pustular scalp swellings with crusting and alopecia, as seen in inflammatory tinea capitis. Typical features: yellow pus, surrounding erythema, and hair loss.

Frequently Asked Questions

Is kerion contagious?

Yes, via spores on hair/skin; isolate until 2-4 weeks of treatment.

Can kerion cause permanent hair loss?

Yes, if longstanding or scarring occurs; early treatment usually restores growth.

Is topical cream enough?

No, oral antifungals are essential for deep infection.

Do pets cause kerion?

Often; M. canis from cats/dogs is common—vet check recommended.

How long does treatment last?

Minimum 6-8 weeks; complete course prevents relapse.