What Causes Nail Fungus, Home Remedy + When to See a Doctor

Nail fungus is caused by fungi that multiply in warm, moist environments and enter through small cracks in the nail. You can treat a mild infection with home remedies like tea tree oil, but more advanced cases require medical treatment.Nail fungus (onychomycosis) is a common infection that impacts approximately 10% to 14% of Americans, and up to 50% of adults over age 70.It often starts as a small white or yellow spot, and can gradually thicken, discolor, and distort the nail if left untreated. Here are its common causes, a popular home remedy for mild cases, and when to see a doctor.

What causes nail fungus on feet?

Fungi are microscopic organisms that naturally live on the skin, hair, and nails. They thrive in warm, moist environments–such as inside tight, non-breathable shoes–which makes toenails particularly susceptible.These organisms can multiply and enter the nail through tiny cracks in the nail or surrounding skin. Once beneath the nail plate, they’re difficult to get rid of.The most common culprits include:

• Dermatophytes (fungi that feed on keratin in skin and nails), especially Trichophyton rubrum and Trichophyton mentagrophytes
• Yeasts, such as Candida species
• Non-dermatophyte molds

Dermatophytes account for up to 90% of cases–particularly in toenail infections.Your risk of nail fungus increases with:

• Tight or non-breathable footwear
• Sweaty feet
• Walking barefoot in locker rooms or pools
• Nail injuries or repeated trauma
• Diabetes
• A weakened immune system
• Aging, which slows nail growth and circulation

While fungal infections affect toenails more frequently due to moisture trapped inside shoes, they can also develop in fingernails–especially after: 

• Nail trauma
• Frequent water exposure
• Artificial nail use

Signs and symptoms of nail fungus

Nail fungus typically doesn’t cause pain at first, so many people overlook it in the early stages. As the infection develops, it can trigger:

• Yellow, white, or brown discoloration
• Thickened nails
• Brittle, crumbly, or ragged edges
• Distorted nail shape
• Dullness or loss of shine
• Occasional odor
• Nail lifting from the nail bed (onycholysis), which can be painful

As the fungus spreads, it also thickens the nail and makes it harder to trim. 

Types of nail fungus

There are two common forms of nail fungus:

Distal subungual onychomycosis (DSO)

This is the most prevalent type. The infection starts under the tip of the nail and spreads beneath the nail plate, often involving the nail bed. This is the type that typically causes:

• Thickening
• Discoloration
• Lifting of the nail (onycholysis)

Superficial onychomycosis

This type affects only the surface layers of the nail and typically appears as white, powdery patches. While often milder at first, it can progress if left untreated, leading to rough, brittle, or crumbling nail surfaces.

Nail fungus home remedy: Tea tree oil

While research on using tea tree oil for nail fungus is mixed, this essential oil does possess antibacterial and antifungal properties.Some test-tube studies suggest it may specifically inhibit the growth of Trichophyton rubrum, a common fungus responsible for nail infections. To try this remedy, experts recommend making a 5%-15% dilution of tea tree oil in a carrier oil such as coconut, olive, or jojoba oil.Apply this mixture to the affected nail twice daily with a clean cotton swab.