By Mayo Clinic Staff
Nail fungus is a common condition that begins as a white or yellow spot under the tip of your fingernail or toenail. As the fungal infection goes deeper, nail fungus may cause your nail to discolor, thicken and crumble at the edge. It can affect several nails but usually not all of them.
If your condition is mild and not bothering you, you may not need treatment. If your nail fungus is painful and has caused thickened nails, self-care steps and medications may help. But even if treatment is successful, nail fungus often comes back.
Nail fungus is also called onychomycosis (on-ih-koh-my-KOH-sis) and tinea unguium. When fungus infects the areas between your toes and the skin of your feet, it’s called athlete’s foot (tinea pedis).
You may have nail fungus — also called onychomycosis (on-ih-koh-my-KOH-sis) — if one or more of your nails are:
Brittle, crumbly or ragged
Distorted in shape
Dull, with no shine
A dark color, caused by debris building up under your nail
Infected nails also may separate from the nail bed, a condition called onycholysis (on-ih-KOL-ih-sis). You may feel pain in your toes or fingertips and detect a slightly foul odor.
When to see a doctor
You may want to see a physician if self-care steps haven’t helped. Also see a doctor if you have diabetes and think you’re developing nail fungus.
Nail fungal infections are typically caused by a dermatophyte fungus. Yeasts and molds also can be responsible for nail fungal infections.
What are fungi?
Fungi are microscopic organisms that don’t need sunlight to survive. Some fungi have beneficial uses. Others cause illness and infection. Fungi:
Live in warm, moist environments, including swimming pools and showers
Can invade your skin through cuts so tiny you can’t even see them or through a small separation between your nail and nail bed
Can cause problems if your nails are often exposed to warm and moist conditions
Toenails vs. fingernails
Nail fungus occurs more often in toenails than in fingernails, partly because:
Toenails often are confined in a dark, warm, moist environment — inside your shoes — where fungi can thrive
Toes usually have less blood flow than do fingers, making it harder for your body’s immune system to detect and stop infection
Factors that can increase your risk of developing nail fungus include:
Being older, owing to reduced blood flow, more years of exposure to fungi and slower growing nails
Being male, especially if you have a family history of nail fungal infections
Working in a humid or moist environment or in a job where your hands are often wet, such as bartending or housekeeping
Wearing socks and shoes that hinder ventilation and don’t absorb perspiration
Living with someone who has nail fungus
Walking barefoot in damp communal areas, such as swimming pools, gyms and shower rooms
Having athlete’s foot
Having a minor skin or nail injury or a skin condition, such as psoriasis
Having diabetes, circulation problems, a weakened immune system or, in children, Down syndrome
A severe case of nail fungus can be painful and may cause permanent damage to your nails. And it may lead to other serious infections that spread beyond your feet if you have a suppressed immune system due to medication, diabetes or other conditions.
If you have diabetes, you may have reduced blood circulation and nerve supply in your feet. You’re also at greater risk of a bacterial skin infection (cellulitis). So any relatively minor injury to your feet — including a nail fungal infection — can lead to a more serious complication. See your doctor if you have diabetes and think you’re developing nail fungus.