What are the different nail fungus types?

Nail fungus is a common infection of one or more fingernails or toenails. While not typically painful, nail fungus, known as onychomycosis, can be unsightly, and if it’s not treated, it can spread to other nails or other people. Different types of nail fungus may typically cause different types of discoloration, but sometimes it’s not always easy to tell what type of fungus is causing the infection just by looking at the nail.

Toenail fungal infections are more common than fingernail fungal infections. This could be because toenails spend more time in the dark, moist environment of shoes and socks, where many types of fungus thrive. Also, people’s feet may come into contact more frequently with walking surfaces that have Athlete’s foot fungus, which is a dermatophyte that can also cause toenail fungus. A dermatophyte is a fungus that requires keratin from hair, skin or nails to thrive. Nail fungal infections caused by dermatophytes are also known as tinea unguium.

When a fungal infection caused by dermatophytes infects the skin under the nail or nail bed, it’s known as distal subungual onychomycosis. Less commonly, the fungus may infect the base or cuticle of the nail while spreading to any new nail growth. In these cases, it’s known as proximal subungual onychomycosis.

Nails infected by dermatophytes may thicken, become brittle and turn yellowish brown.

Mostly caused by dermatophytes and less commonly by nondermatophyte molds or yeast, this type of fungal nail infection accounts for a smaller percentage of nail infections and only affects the top layer of the nail. It starts as white spots, which may spread across the nail and make it rough or crumbly. Spots may become flaky and pitted.

In some cases, fungal nail infections are caused by yeast, another type of fungus. The most common culprit is a Candida infection, which generally occurs in the fingernails. Yeast infections of the nails generally start near the cuticle or tissue around the nail (paronychia), causing it to become red, tender and swollen.

Fungal infections of the nails are typically harmless for healthy people, but for those with chronic diseases like diabetes or those who have a compromised immune system, any type of nail fungus can turn dangerous. Even in healthy individuals, nail fungus that’s left untreated may spread to other fingernails or toenails, and it can also spread to other people. In severe cases, the nail may lift off or fall completely off the nail bed. Treatment for any type of nail fungus may involve over-the-counter antifungal treatments, prescription antifungal creams or more effective oral antifungal medications.

Visit your healthcare provider at the first sign of a fungal nail infection to identify the type of infection and improve treatment outcomes. To determine the type of nail fungus you have, your healthcare provider will examine the nail, which could be enough to make a diagnosis. If necessary, your provider may take a sample scraping to send to the lab in order to identify the organism causing the infection.

Updated by Julie McDaniel, MSN, RN, CRNI, October 2024.