Ringworm: Causes, Symptoms, and Treatment

Ringworm is a skin infection caused by a fungus. It's highly contagious and spreads easily by skin-to-skin contact, meaning you can get ringworm by touching someone with the infection. Ringworm also can be passed along from animals and pets, especially puppies and kittens. It's even possible to get ringworm from objects—by sharing hats, for example.

Research shows that fungal infections of skin and/or nails affect as much as 20% to 25% of the world's population and can affect anyone at any age. Children are especially susceptible to ringworm.

Ringworm is easy to recognize, treat, and prevent, and rarely causes serious complications.

Types of Ringworm

What is ringworm? The name of the ringworm rash comes from its circular shape—it has nothing to do with worms. It is a fungal infection that can affect the skin, hair, and nails. Clinical names for ringworm include tinea and dermatophytosis.

Ringworm also is known by other names according to where on the body it appears.

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Ringworm Symptoms

Ringworm isn't hard to recognize once it develops its characteristic circular rash. Sometimes, though, ringworm symptoms can be confused with other skin rashes.

On most parts of the body, ringworm starts out as a flat, scaly lesion that gradually develops a border before extending outward to create a circular ring shape. On lighter skin, the rash can appear red, but on darker skin tones, it could be brown or even gray in color.

The border of the rash is usually raised and scaly, while the central area is typically flat with fine scaling. Some ringworm infections develop vesicles (fluid-filled blisters) caused by the immune system's exaggerated response to the infection.

Ringworm can look different on certain parts of the body. Athlete's foot, for example, usually causes an itchy, patchy rash with cracking (fissuring) and scaling between the toes.

Ringworm on the scalp (tinea capitis) also has unique symptoms. The most common symptom is hair loss. This can be accompanied by what is sometimes called black dot—a patch of hair loss with black dots on the scalp caused by hairs that are broken off just below the surface of the skin. Hair loss may also be accompanied by boggy, thickened skin and blisters on the scalp, a condition called kerion.

On the scalp, the ringworm rash can look different depending on whether the fungus gets inside the hair shaft or stays on the outside.

What Causes Ringworm?

Approximately 40 different species of fungi can cause ringworm, according to the CDC. The scientific names for these fungi are Trichophyton, Microsporum, and Epidermophyton.

These dermatophytes survive on dead keratin, a protein in the top layer of the epidermis. Keratin also is found in the hair and nails, which is why the toes, feet, and scalp are so susceptible to fungal infections.

Diagnosis

Ringworm infection is pretty self-apparent, given its unmistakable appearance. However, ringworm can sometimes mimic other skin conditions, including granuloma annulare, eczema, and tinea versicolor. The same can be said for infections of the scalp, which are often hard to distinguish from psoriasis or seborrheic dermatitis. 

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A primary care physician or dermatologist likely will be able to diagnose ringworm simply by looking at it. But when it's not clear that a fungal infection is the cause of a rash, a skin culture known as a KOH test can provide proof. This test involves taking a scraping of infected skin and looking at it under a microscope using a potassium hydroxide (KOH) stain in order to identify fungal hyphae or branches.

Sometimes a healthcare provider will use a special light called a Wood's lamp to diagnose a fungal infection. When illuminated by the light, hairs affected by a fungus will show up as blue-green in color.

Treatment

Ringworm doesn't always go away on its own and should be treated. When not treated properly, ringworm can lead to a number of complications (including the spread of the infection to other parts of the body, bacterial skin infections, and skin disorders such as contact dermatitis).

There are numerous approaches to treating ringworm infections, depending in large part on the region of the body affected. Treatments include:

• Over-the-counter (OTC) and prescription topical antifungal creams or ointments applied directly to fungal lesions
• Antifungal shampoos used to treat infections of the scalp
• Oral medications for fungal infections that are resistant to topical treatments

There are also a few natural approaches for treating ringworm that have shown promise in studies, including tea tree oil for athlete's foot and garlic extract.

Outlook

Fungal infections of the skin can be itchy, uncomfortable, and even cause unsightly and stare-provoking lesions. Tinea on the head can result in bald patches. And when a fungus gets hold of fingernails or toenails, not even the most expert manicure or pedicure is likely to mask the problem. 

On the other hand, fungal infections almost always are easy to treat, and there are many effective steps you can take to prevent them based on common sense and good hygiene. If you, your child, or a beloved pet brings home a fungal infection, getting a prompt diagnosis, following your healthcare provider's orders for treatment, and taking measures to protect the rest of the family from infection should be all it takes to banish tinea from your household.