Kerion - Causes, Treatment & When to See a Doctor

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What is Kerion?

Kerion is an inflamed, painful, and often pus‑filled scalp lesion that results from a severe allergic reaction to a fungal infection of the hair follicles—most commonly dermatophytes that cause *tinea capitis* (scalp ringworm). The word “kerion” comes from the Greek kéras, meaning “horn,” describing the thick, horn‑like crust that can develop over the lesion. It is most frequently seen in children, but adults can be affected, especially if they have close contact with infected pets or live in crowded settings.

Unlike a simple fungal scalp infection that may cause mild scaling and itching, kerion is a pronounced inflammatory response that can mimic bacterial abscesses or even skin cancer. Early recognition is essential to avoid unnecessary surgery, permanent hair loss, or systemic spread of infection.

Common Causes

Kerion is not a disease itself; it is a reaction to underlying fungal organisms or, less often, bacterial agents. The most frequent culprits are:

• Trichophyton tonsurans – the leading cause of tinea capitis in North America and parts of Europe.
• Trichophyton violaceum – common in the Mediterranean, Middle East, and Africa.
• Microsporum canis – transmitted from cats and dogs; responsible for many zoonotic cases.
• Microsporum audouinii – historically a major cause in England and Scandinavia.
• Trichophyton mentagrophytes – less common, but can cause severe reactions.
• Secondary bacterial infection (often Staphylococcus aureus) that complicates a fungal lesion.
• Allergic hyper‑response to fungal antigens – the immune system overreacts, producing the painful swelling.
• Improper use of topical steroids on an undiagnosed fungal infection (can worsen inflammation).
• Contact with contaminated objects (comb, pillow, hats) that harbor fungal spores.
• Immunocompromised states (e.g., HIV, chemotherapy) that predispose to atypical presentations.

Associated Symptoms

Because kerion is an inflammatory reaction, it usually appears with several other signs:

• Intense, throbbing pain at the affected scalp area.
• Swelling that can spread beyond the primary lesion.
• Yellow‑white or purulent (pus‑filled) crusts that may ooze.
• Hair loss (alopecia) in the center of the lesion; hairs may break off easily.
• Fever, chills, or malaise in 30‑40 % of cases, especially when secondary bacterial infection is present.
• Regional lymphadenopathy – tender lymph nodes in the neck.
• Itching or burning sensation before the lesion becomes painful.
• Occasionally, a “boggy” consistency (soft, spongy feel) beneath the crust.

When to See a Doctor

Kerion can progress quickly, so prompt medical evaluation is advisable when any of the following occur:

• Sudden onset of a tender, swollen scalp lump that does not improve after a few days.
• Fever ≥ 38 °C (100.4 °F) or chills accompanying the scalp lesion.
• Visible pus, foul odor, or rapidly enlarging crust.
• Swollen or painful neck lymph nodes.
• Noticeable hair loss in a patchy, irregular pattern.
• History of contact with an infected child, pet, or shared personal items.
• Any sign of spreading redness beyond the original lesion (possible cellulitis).
• Previous use of potent steroids on the scalp that worsened the problem.

Even if the lesion appears “small,” children should be examined because early treatment reduces the risk of permanent scarring alopecia.

Diagnosis

Accurate diagnosis relies on a combination of clinical exam, laboratory testing, and sometimes imaging:

1. Clinical assessment – A dermatologist or primary‑care provider will look for the classic “boggy,” tender, and crusted plaque with broken hairs.
2. Wood’s lamp examination – Certain species (e.g., M. canis) fluoresce green under ultraviolet light, aiding rapid identification.
3. Microscopic examination – A hair‑pluck or skin‑scraping sample is placed on a slide with potassium hydroxide (KOH). The KOH dissolves keratin, revealing fungal hyphae or spores under the microscope.
4. Fungal culture – Samples are grown on Sabouraud agar for 2‑4 weeks. Culturing confirms the exact species, which guides drug choice.
5. Polymerase chain reaction (PCR) – More rapid (24‑48 h) molecular testing that detects dermatophyte DNA and is increasingly available in reference labs.
6. Bacterial culture – If there is pus, a swab may be taken to rule out or treat secondary bacterial infection.
7. Imaging (rare) – In extensive lesions, an ultrasound can delineate the depth of the abscess, but this is not routine.

Doctors will also ask about recent exposures, travel history, and underlying health conditions to tailor management.

Treatment Options

Kerion requires systemic (oral) antifungal therapy, not just topical creams. The goals are to eradicate the fungus, reduce inflammation, and prevent permanent hair loss.

Medical Therapy

• Oral antifungals (first‑line)
  • Griseofulvin – 20–25 mg/kg/day for 6–8 weeks; historically the drug of choice.
  • Terbinafine – 250 mg daily for 4 weeks (children 62.5 mg daily); often preferred for T. tonsurans because of shorter course.
  • Itraconazole – 5 mg/kg/day for 4 weeks; useful for resistant strains.
  • Luliconazole or fluconazole – alternative agents in selected cases.
• Adjunctive corticosteroids – A short course of oral prednisone (0.5 mg/kg for 5‑7 days) can dampen the intense inflammatory response and reduce swelling, particularly when the lesion is very large or painful. This is used **only** after confirming a fungal cause; steroids can worsen an untreated bacterial infection.
• Antibiotics – If bacterial superinfection is suspected (purulent drainage, high fever, positive cultures), agents such as cephalexin or clindamycin are added.

Supportive & Home Care

• Gentle cleansing with a mild, non‑irritating shampoo (e.g., baby shampoo) twice daily.
• Applying a warm compress for 10‑15 minutes, 3‑4 times a day to relieve pain and promote drainage.
• Keeping the hair and scalp clean and dry; avoid tight hats or headbands that trap moisture.
• Do not pick, scratch, or try to “pop” the lesion—this can spread infection and increase scarring.
• Disinfect personal items (comb, pillowcase, hats) with hot water (> 60 °C) or bleach solution.
• Family members should be examined and possibly treated prophylactically if they show early signs of tinea capitis.

Follow‑up

Patients are usually re‑evaluated after 2‑3 weeks of therapy to ensure the lesion is regressing. Hair regrowth can take 3‑6 months; persistent alopecia may need dermatologic referral for potential hair‑transplant or scalp‑microneedling techniques.

Prevention Tips

Because kerion stems from a contagious fungal infection, many preventive steps focus on limiting exposure and maintaining scalp hygiene:

• Avoid sharing hats, headbands, hairbrushes, pillows, or helmets.
• Wash bedding and personal items weekly in hot water; add a cup of white vinegar for extra antifungal effect.
• Promptly treat any tinea capitis in family members; untreated cases are the greatest source of spread.
• Inspect children’s scalps after playdates, school, or sports where close head contact occurs.
• Limit contact with stray or unvaccinated animals; if a pet is suspected of carrying M. canis, seek veterinary evaluation and treat with appropriate topical or oral antifungals.
• Use antifungal “shampoo‑plus” products (e.g., selenium sulfide 2.5 % lotion) as a prophylactic measure in households where an infection has occurred.
• Maintain good personal hygiene—regular bathing and drying of the scalp after swimming or sweating.
• Educate school staff and caregivers about the signs of scalp ringworm and the importance of early referral.

Emergency Warning Signs

Key Take‑aways

Kerion is a painful, inflammatory scalp lesion that signals a severe reaction to a fungal infection, most often caused by dermatophytes such as Trichophyton tonsurans or Microsporum canis. Prompt medical evaluation, laboratory confirmation, and systemic antifungal treatment—often combined with a short course of steroids—are essential to prevent permanent hair loss and complications. Good scalp hygiene, avoidance of shared personal items, and early treatment of tinea capitis in contacts are the cornerstone of prevention.

For the most reliable, up‑to‑date information, references include:

• Mayo Clinic. “Tinea capitis (scalp ringworm).” 2024.
• Cleveland Clinic. “Kerion – inflammatory scalp ringworm.” 2023.
• Centers for Disease Control and Prevention (CDC). “Fungal Diseases – Dermatophyte Infections.” 2022.
• National Institutes of Health (NIH) – Clinical Guidelines for Dermatophyte Infections. 2023.
• World Health Organization (WHO). “Skin NTDs: Guidelines for Diagnosis and Management.” 2021.

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