Introduction

A kerion (keer-ee-on) is a severe inflammatory form of a fungal infection that mainly affects the scalp and hair (also known as tinea capitis or scalp ringworm) due to an exaggerated immune reaction against the fungal pathogens responsible (i.e. dermatophytes).¹ A kerion appears as big, yellow, pus-filled sores (abscesses) on the head, often leading to hair loss.² The causes and risk factors associated with a kerion include poor scalp hygiene, having close contact with an infected person, using other people’s personal hair items and late or incorrect treatment of the existing fungal infection.³ The two main groups of fungi responsible for the infection are Microsporum and Trichophyton.¹ They can infect keratin and keratinised tissues such as the hair and outer layer of the skin.⁴ It is essential to understand the exact causes and the type of fungus that causes the infection, so that healthcare professionals can diagnose and plan the most appropriate treatment. If the infection is not treated, it could harm the scalp and cause permanent hair loss.²

Causes and risk factors associated with kerion

• An overactive immune reaction due to the existing fungal infection that affects the scalp and hair (also known as Tinea Capitis or Scalp Ringworm).¹ The fungi penetrate the outer root sheath, a protective layer of the hair follicle, and potentially the hair shaft.⁴ The body then produces an exaggerated immune response, causing more damage than the actual infection itself. A kerion may also appear on the face, neck, shoulders and upper arms if a fungal infection develops there²
• Poor scalp hygiene – Not washing your hair or cleansing your scalp properly can create a warm, moist environment that is perfect for fungal growth
• Scalp injuries – Cuts and scratches on the scalp provide direct entry points for fungus⁵
• Direct contact with an infected person/animal - The risk of getting a fungal infection and a kerion can be increased due to close contact with an infected person/animal, staying in overcrowded spaces or sharing personal items such as combs and hats³
• Improper or delayed treatment of the fungal infection can worsen the condition to produce kerions. The prolonged skin inflammation may also lead to a different bacterial skin infection as well³
• Other risk factors: Diabetes mellitus, eczema, prolonged steroid use, immunosuppressant medication, anaemia and cancer⁴ 

Fungal species commonly associated with kerion

Dermatophyte fungi are typically found in this type of fungal infection that causes a kerion to develop.⁶ They can infect keratin (a protein) and keratinised tissue, including the hair and outer layer of skin. They require keratin and a moist, warm environment to grow. The infection may be transmitted through direct contact with the organisms from animals (zoophilic), soil (geophilic) and humans (anthrophilic).⁴

The fungal infection is mainly caused by different Microsporum and Trichophyton species,⁷ specifically noting Microsporum canis and Trichophyton tonsurans.⁸

Microsporum

Microsporum canis (M. canis) is a fungus commonly transmitted from infected cats and dogs.⁸ It is the most common dermatophyte to cause human tinea capitis in Europe as well as South America.⁹ They are an ectothrix species; this means that they will grow within the hair follicle and cover the outer layer of the hair shaft (strand) while damaging the cuticle (outermost layer of the hair strand).¹⁰ The infection of this fungus will result in severe itching of the scalp and hair loss. The infection will fluoresce a bright yellow-green under a special type of ultraviolet (UV) light known as Wood’s ultraviolet light, which is useful for diagnostic purposes.¹¹

Trichophyton

Trichophyton tonsurans (T. tonsurans) is the most common cause in humans, especially in North and Central America.¹² They are an endothrix species; this means that they grow within the hair shaft, but do not damage the cuticle.¹⁰ This infection will not fluoresce under Wood’s UV light.¹³

Other species that cause infection include Trichophyton mentagrophytes, Trichophyton verrucosum (common with infected cattle) and Trichophyton rubrum (less common).¹³

A kerion may be confused with other conditions such as bacterial folliculitis, infected eczema, pustular psoriasis and seborrheic dermatitis.⁴ Therefore, the use of proper diagnostic tools is necessary. Trichoscopy, a magnified, non-invasive examination, is another common diagnostic tool for differentiating fungal infection, providing information for accurate treatment decisions.¹⁴ 

FAQs

Is it contagious?

Yes, a kerion is contagious. The fungal infection can spread by having close contact with another infected person or by sharing personal items such as hair combs, brushes, accessories and hats/towels.²

Can there be other secondary conditions related to this?

Due to this inflammatory fungal infection affecting the scalp and the hair, the hair will eventually become brittle and break; therefore, there will be scarring alopecia (hair loss) present. The infection may also affect beards, eyelashes and eyebrows and potentially the skin of the face, shoulder, neck and upper body. Kerions can also cause stress, anxiety and depression, especially if you are worrying about how other people see you, and so it may influence your self-perception and behaviour.²

Who is most likely to develop a fungal infection and kerion?

Children between 3 and 14 years of age are most likely to develop a fungal infection and kerion;⁴ therefore, it is important to inquire about colleagues and friends from school who may have the same condition. However, it may affect any age group depending on other risk factors present, such as a compromised immune system. There are cases of these infections all over the world; however, it is most common in hot, humid countries such as those in Africa, Central America and Southeast Asia.⁴

What can I do to take care of myself? (Self-care)

To prevent the fungus from spreading to other people, it is important to stay clean with good hygiene; make sure that your head (and other areas that have hair) is kept clean and dry. Try to avoid sharing hair tools/accessories (e.g combs, brushes, hair bands), hats, towels, helmets, or pillowcases with other people, as the fungus likes to grow within places. Also, try to avoid using shared public items such as gym mats. It is best to clean them with simple bleach (if possible) or wash towels, hats and bedding at high temperatures, or get new ones. To stop the fungus spreading, do not visit the hairdresser's/barbers and take precautions when visiting overcrowded spaces like the gym or school.

How do you treat a kerion?

A kerion is typically treated with oral antifungal medication. Examples of common treatments include griseofulvin, terbinafine, fluconazole or itraconazole. Topical medication (creams) will not be effective.²

Will my hair grow back after my kerion is gone?

After appropriate treatment and self-care, hair will regrow; however, if left untreated or if the infection persists for prolonged periods of time, there is a chance that the hair loss will be permanent due to scarring.²

What’s the main difference between a kerion and other scalp abscesses?

A kerion and other scalp abscesses are both inflamed, pus-filled sores/bumps, but the main difference between the two is down to the underlying cause. A scalp abscess is primarily formed due to a bacterial infection,¹⁵ whereas a kerion is specifically caused by a fungal infection. Therefore, it is important to seek medical evaluation and explain all the symptoms you are experiencing to a healthcare professional for an accurate diagnosis and treatment. 

Summary

A kerion is caused by an exaggerated immune reaction to a fungal infection that mainly affects the scalp and hair, not just by the fungus itself. It can present itself as a pus-filled, crusted sore/bumps. The fungal infection can develop due to poor hygiene, being in direct contact with an infected person or sharing personal hair items with an infected person. A kerion may develop due to delayed or improper treatment of the primary fungal infection. The two main fungal species that are commonly isolated include Microsporum canis and Trichophyton tonsurans. Tools like trichoscopy and Wood’s UV light are often used to find this kind of fungus and help to determine the kind of fungus it is in the infection.

By knowing the causes and the kind of fungus behind it, we can make sure to treat the kerion well with medication that fights that fungus. If no one treats the infection, it may lead to scars and hair loss for good. Since the infection and a kerion can spread to other people, it is important to stay clean with good hygiene, such as washing hands well and often, especially after petting animals, to stop the fungus from moving to more people. Also, avoiding sharing personal items and minimising contact with infected animals and other people will help.