What Is Ringworm?

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 inanimate objects—by sharing hats, for example.

Research shows that fungal infections of skin and/or nails affect as much as 20 percent to 25 percent of the world's population and can affect anyone at any age. Children are especially susceptible to ringworm. Despite being so prevalent, ringworm is easy to recognize, treat, and prevent, and rarely causes serious complications.

Clinical names for ringworm include tinea and dermatophytosis. The infection has nothing to do with worms. It's classified as a dermatophytic infection. The name comes from the circular shape of the ringworm rash.

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

Ringworm isn't hard to recognize, although it can be confused with other skin rashes. On most parts of the body, ringworm begins as a flat, scaly lesion that gradually develops a border before extending outward to create a circular ring shape.

The border 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 usually causes an itchy, patchy rash with fissuring and scaling between the toes, for example.

The most common symptom of tinea capitis is hair loss. There is also a rash, which can look different depending on whether the fungus gets inside the hair shaft or stays on the outside of the hair shaft.

Ringworm on the scalp can also cause 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; gray patch, areas of hair loss with dry, scaly patches on the scalp; and kerion, areas of hair loss with boggy, thickened scalp and blisters.

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 toes, feet, and scalp are so susceptible to fungal infections.

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. 

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 doctor 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.

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.

Fungal infections of the skin are never pleasant. They 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 doctor'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.