Introduction 

Kerion is a highly inflammatory and painful fungal infection that affects the scalp. It is a complication of tinea capitis, and it is not as well-known in public health circles as other dermatologic conditions.¹ However, its impact—especially when misdiagnosed—can be significant. One of the major challenges with kerion is that it resembles other skin infections, particularly bacterial abscesses or cellulitis.² This similarity in symptoms often results in misdiagnosis and treatment with antibiotics or surgical incision and drainage, both of which are ineffective and can worsen the patient’s condition. In this article, we will discuss what kerion is, how and why it gets misdiagnosed, the dangers of confusing it with a bacterial infection, and how to ensure accurate diagnosis and treatment.

What is kerion?

Kerion is not a distinct disease but rather a severe manifestation of tinea capitis, a fungal infection of the scalp. It occurs when the body mounts an exaggerated immune response to the fungal invader, typically Trichophyton or Microsporum species. The result is a boggy, inflamed, pus-filled swelling on the scalp that can easily be mistaken for an abscess.¹ This exaggerated immune reaction makes the area red, tender, swollen, and sometimes oozing pus.

These features closely resemble those of bacterial infections, which is why even experienced clinicians may initially treat kerion as a staph abscess or cellulitis.² Unfortunately, treatments for bacterial infections do not benefit kerion and, in some cases, can worsen it. Kerion is most common in children aged 3 to 10 years, though it can also occur in adults, especially in immunocompromised individuals or those in close contact with animals or infected persons.^1,2 It often presents as a tender mass with broken hairs, hair loss, and sometimes lymph node swelling in the neck or behind the ears.

Understanding bacterial abscesses and cellulitis

Before we delve into how misdiagnosis occurs, let us first understand the characteristics of a bacterial abscess and cellulitis. Both are common skin and soft tissue infections, and they can resemble kerion in their early stages. A bacterial abscess is a localised collection of pus resulting from a bacterial infection, typically caused by Staphylococcus aureus.³ It is marked by swelling, redness, warmth, and pain at the affected site. The center of the abscess becomes soft and fluctuant as pus builds up. In contrast, cellulitis is a more extensive infection that spreads across a larger area of skin. It appears as a red, swollen, tender area of skin that feels warm to the touch. Patients may experience fever or chills depending on the severity of the infection.^2,3 In both conditions, antibiotics are standard treatment, along with incision and drainage for abscesses. These interventions are effective—unless the diagnosis is kerion. In that case, these treatments may fail and potentially cause harm.

Why is kerion misdiagnosed?

Kerion is misdiagnosed because it resembles other common skin infections. It has swelling, pus, tenderness, and redness – all the signs of an infection.² But these symptoms do not come from the bacteria; they come from the body’s response to the fungus. Additionally, kerion is not well known, especially among general practitioners or emergency care providers who may not see it often. Abscesses and cellulitis are more common, so they are the first diagnoses that come to mind.^2,4 Another factor is that early kerions may not have hair loss or scaling, so it looks like an abscess. In resource-limited settings or busy clinics, fungal testing (KOH prep or fungal culture) may not be available; thus, diagnosis is based on visual inspection alone. Many times, children have undergone surgical drainage for kerion, thinking it is a staph abscess.⁴ These procedures not only fail to solve the problem but also cause pain, scarring, and the risk of secondary bacterial infection.

Clinical clues to distinguish kerion from bacterial infections

Although kerion and bacterial abscesses look similar, there are some subtle clues to differentiate them. First, the kerion develops more slowly than a bacterial abscess.^1-3 While abscesses can develop in 24-48 hours, kerion takes several days to form. The mass is boggy, not tense, and there is usually hair loss or broken hairs over the lesion. Second, kerion does not improve with antibiotics. If the lesion is presumed to be a bacterial abscess and treated with oral antibiotics and does not improve in 48-72 hours, this should raise suspicion for an alternative diagnosis.^2,4 Also, in kerion, regional lymphadenopathy – swollen lymph nodes in the neck or behind the ears – is more common than in uncomplicated bacterial abscesses.⁴ Finally, a history of animal contact (especially with cats or dogs) or contact with other children with scalp infections can point to a fungal origin.

The consequences of misdiagnosis

Misdiagnosing a kerion as a bacterial infection can have serious consequences. One of the most immediate is the delay in treatment. Fungal infections like kerion require systemic antifungal medications, and the longer the treatment is delayed, the higher the risk of scarring and permanent hair loss.^1-3 Another consequence is the use of unnecessary antibiotics, which can contribute to antibiotic resistance and cause side effects like gastrointestinal upset, allergic reactions, or yeast infections.^3,4 Worse still, if the lesion is incised or drained – as is common with abscesses – it can lead to secondary bacterial infection, additional pain, scarring, and psychological trauma, especially in children. Some children may be left with permanent bald spots or thick scarring from repeated wrong treatments. Kerion is also contagious, especially in school or daycare settings.⁴ A misdiagnosed case can lead to outbreaks if other children or family members are not protected or treated.

How is kerion diagnosed?

Diagnosing kerion is a combination of clinical and laboratory tests. The gold standard is a fungal culture that will identify the specific dermatophyte causing the infection. However, this can take up to 4 weeks to get the results.^2,4 In the meantime, clinicians can do a KOH prep test, which involves scraping the skin and looking under the microscope for fungal elements. It will give rapid preliminary results. A Wood’s lamp examination may also be executed. Some fungi will fluoresce under UV light, which will help confirm the diagnosis.⁴ However, not all fungal species that cause kerion will glow under this light. In some cases, especially if the diagnosis is uncertain or the lesion is atypical, a skin biopsy may be done to rule out other conditions.

Effective treatment for kerion

Once diagnosed, kerion must be treated promptly and aggressively to prevent complications. Topical antifungals are not enough. Oral antifungals are required. The most commonly prescribed medication is griseofulvin, which is often used in children.² Treatment is 6-8 weeks, and compliance is key to full recovery. In adults, or if griseofulvin is not effective or tolerated, terbinafine, itraconazole, or fluconazole may be prescribed.^2,4 In very inflamed cases, a short course of oral corticosteroids may be added to reduce swelling and pain. However, this should be used with caution and always with antifungal therapy. Some patients may need additional treatment for any secondary bacterial infection that occurs due to scratching or previous drainage attempts.

When to get a second opinion

If you or your child has a scalp lesion that has not responded to antibiotics or has worsened despite treatment, you should get a second opinion, preferably from a dermatologist.¹ Specialists are more familiar with fungal conditions like kerion and can do the necessary diagnostic tests and treatments. You should also get a second opinion if surgical drainage is recommended for a scalp lesion, especially in a child.^2,5 Remember, kerion should not be incised, and doing so can cause permanent damage.

Preventing misdiagnosis and protecting patients

Awareness is the best defense against misdiagnosis, both within healthcare providers and the general public. Family practitioners, pediatricians, and emergency room personnel must include kerion in their differential diagnosis of scalp abscesses, especially in children.^2-4 Parents need to be cognisant of checking for any signs of scalp infection and should be able to relay any recent history of ringworm exposure (e.g., infected dog), school outbreaks, infections in playmates, or Islander/cross-fit gym exposures.^4,5 Timely dermatologic referral and fungal culture can prevent unnecessary trauma from inappropriate treatment.

FAQs

1. Is kerion contagious?

Yes, kerion can be transmitted through direct contact or sharing personal items such as combs, hats, or bedding.

2. Can kerion heal on its own?

No, it will not heal on its own; it requires oral antifungal treatment. If the kerion is not treated appropriately, it will worsen or become permanently scarred.

3. What is the cause of a kerion?

A kerion is a fungal infection, most commonly caused by dermatophytes, such as species of Trichophyton or Microsporum. Kerions are an example of a hypersensitive immune response to these organisms.

4. How long does it take for a kerion to heal?

Visible signs of improvement with treatment will usually occur after 1-2 weeks, but healing can take 6-8 weeks or longer.

5. Will the hair grow back?

If identified and treated early, yes, hair typically regrows. If treated later, and especially in cases when the hair is surgically shaved, there is a possibility of permanent hair loss or scarring.

Summary

Kerion is a serious but treatable condition frequently misdiagnosed as a bacterial abscess or cellulitis. This clinical error can delay healing, scarring, and subject patients to unnecessary treatments. Knowledge of kerion’s presentation and recognition of its distinct differences from bacterial infections is essential for early diagnosis. Parents, caregivers, and healthcare providers should always consider kerion in the differential diagnosis list, especially when scalp lesions are not improving with antibiotics. The correct diagnosis can make the difference between resolution or chronicity and a significant consequence or none at all for the patient. When in doubt, request a fungal test. It may spare the patient from unnecessary procedures and facilitate adequate treatment from the outset.