Onychomycosis (Fungal Nail Infection)

What onychomycosis is

The word combines Greek onyx (nail) and mykes (fungus). Fungi invade the nail plate, the nail bed underneath, or both. Because nails grow slowly and have no blood supply in the plate, the infection is hard to reach and clears slowly.

Most cases (around 90 in 100 toenail infections) are caused by dermatophytes, mainly Trichophyton rubrum, which also causes athlete's foot. Yeasts such as Candida more often affect fingernails, especially in people whose hands are often wet. Non-dermatophyte molds cause a minority of cases. When a dermatophyte causes it, the term tinea unguium is also used.

Symptoms

• Yellow, white, brown or gray discoloration
• Thickening that makes the nail hard to cut
• Crumbly, brittle or ragged edges
• Debris building up under the nail
• The nail lifting off the nail bed (onycholysis)
• Distorted shape, and sometimes a slight odor
• Discomfort or pain in tight shoes once the nail is very thick

The big toenail is affected first in most people. Fingernail infection is less common and often comes with toenail infection or chronic wet-work exposure.

Types of onychomycosis

Causes and risk factors

Fungi thrive in warm, moist places and get under the nail through tiny cracks or a separated edge. Risk is higher with:

• Age: slower nail growth and poorer circulation
• Athlete's foot, which spreads to the nails
• Diabetes, poor circulation, or a weakened immune system
• Damage to the nail, from sports, tight shoes or repeated trauma
• Psoriasis, which damages nails and makes them prone to infection
• Sweaty feet, occlusive footwear and walking barefoot in communal showers, pools and gyms
• Family members with fungal infection
• Smoking

Diagnosis

Many nail conditions look like fungus, so the American Academy of Dermatology recommends confirming the diagnosis before starting oral treatment. About half of thick, discolored nails are not fungal.

• Nail clippings or scrapings from under the nail are sent for microscopy with potassium hydroxide (KOH), fungal culture, PCR, or a stain of nail tissue (PAS).
• A dermatologist or podiatrist may use dermoscopy to look at the nail pattern.

Conditions that mimic nail fungus

• Nail psoriasis: pitting, oil-drop yellow-orange spots, often in several nails and with skin psoriasis
• Nail trauma: thick, lifted or discolored nails from repeated pressure, often in runners
• Bacterial infection with Pseudomonas: green-black discoloration
• Lichen planus of the nail
• Melanoma under the nail: a dark streak, changing in width, or pigment on the surrounding skin

Treatment

Not everyone needs treatment. Mild cases that cause no symptoms can be left alone, or kept trimmed. Treatment is worth considering if the nail is painful, you have diabetes or poor circulation, the infection is spreading, or you dislike the look.

Oral antifungal tablets

• Terbinafine is the most effective option for dermatophyte infection. A course typically lasts about 6 weeks for fingernails and 12 weeks for toenails.
• Itraconazole is an alternative, sometimes given in pulses, and works against yeasts too.
• Fluconazole is used off-label in some cases.

The drug stays in the nail after you stop, and the healthy nail has to grow out. A toenail takes 12 to 18 months to grow fully. Your doctor may check liver blood tests, and will review your other medicines because itraconazole interacts with many drugs. Stop and contact your doctor if you develop yellow skin or eyes, dark urine, severe tiredness or a rash.

Topical treatments

• Medicated nail solutions such as efinaconazole, tavaborole and ciclopirox lacquer are applied daily for about 48 weeks.
• They work best for mild infection, white superficial type, or when tablets are not suitable.
• Filing the nail thin first helps the medicine penetrate.

Other options

• Laser and light treatments: may improve appearance, but evidence for a lasting cure is limited, and they are usually not covered by insurance.
• Nail removal: surgical or chemical removal of a painful nail, usually combined with antifungal medicine.
• Regular debridement: a podiatrist trims and thins thick nails to reduce pain.

Do home remedies work?

Over-the-counter creams for athlete's foot do not penetrate the nail well. Tea tree oil, vinegar soaks and vapor rubs have weak evidence. They are unlikely to cause harm, but they rarely clear an established infection.

Complications

For most people, nail fungus is a cosmetic and comfort problem. In people with diabetes or poor circulation, thick, sharp nails can cut the skin and lead to diabetic foot infections or cellulitis. Ongoing infection can also seed athlete's foot.

Preventing reinfection

Recurrence is common, affecting up to 1 in 4 to 1 in 2 people after treatment. To lower the risk:

• Treat athlete's foot promptly and use antifungal powder in shoes.
• Dry feet well, especially between toes, and wear moisture-wicking socks.
• Wear sandals in communal showers, gyms and pools.
• Keep nails short and straight across, and do not share clippers.
• Replace or disinfect old shoes.

Frequently asked questions

What is onychomycosis?

Onychomycosis is a fungal infection of the fingernails or toenails. It causes thick, discolored, crumbly nails that may lift from the nail bed. It is usually caused by dermatophyte fungi, the same organisms responsible for athlete's foot.

What is the most effective treatment for onychomycosis?

Oral terbinafine is the most effective treatment for the common dermatophyte type, typically taken for about 12 weeks for toenails. Topical medicated solutions help milder cases. Because the nail grows slowly, it takes 12 to 18 months to see a fully clear toenail.

Is onychomycosis contagious?

It is mildly contagious. The fungi spread through damp floors, shared clippers and footwear, and from athlete's foot on your own skin. Close contacts often share the infection, so treating everyone in a household may reduce recurrence.

Will onychomycosis go away on its own?

Rarely. Without treatment, onychomycosis usually persists or slowly spreads to other nails. It is not harmful for most healthy people, so leaving mild cases untreated is a reasonable choice.

How do I know if it is nail fungus or something else?

You cannot be sure by looking. Psoriasis, injury and other conditions cause similar thick, discolored nails. A doctor can send a nail clipping to a lab to confirm fungus before you take months of treatment.