An infection of nail fungus occurs when fungi infect one or more of your nails. A nail fungal infection may begin as a white or yellow spot under the tip of your fingernail or toenail. As the nail fungus spreads deeper into your nail, it may cause your nail to discolor, thicken and develop crumbling edges — an unsightly and potentially painful problem.

These infections usually develop on nails continually exposed to warm, moist environments, such as sweaty shoes or shower floors. Nail fungus isn't the same as athlete's foot, which primarily affects the skin of the feet, but at times the two may coexist and can be caused by the same type of fungus.

An infection with nail fungus may be difficult to treat, and infections may recur. But medications are available to help clear up nail fungus.

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Nail fungal infection

You may have a nail fungal infection — also called onychomycosis (on-i-ko-mi-KO-sis) — if one or more of your nails are:

• Thickened
• Brittle, crumbly or ragged
• Distorted in shape
• Dull, with no luster or shine
• A dark color, caused by debris building up under your nail

Infected nails may also separate from the nail bed, a condition called onycholysis. You may even feel pain in your toes or fingertips and detect a slightly foul odor.

Fungi are microscopic organisms that don't need sunlight to survive. Some fungi have beneficial uses, while others cause illness and infection.

Nail fungal infections are typically caused by a fungus that belongs to a group of fungi called dermatophytes. But yeasts and molds also can be responsible for nail fungal infections.

All of these microscopic organisms live in warm, moist environments, including swimming pools and showers. They can invade your skin through tiny invisible cuts or through a small separation between your nail and nail bed. They cause problems only if your nails are continually exposed to warmth and moisture — conditions perfect for the growth and spread of fungi.

Infection with nail fungus occurs more in toenails than in fingernails because toenails are often confined in a dark, warm, moist environment inside your shoes — where fungi can thrive. Another reason may be the diminished blood circulation to the toes as compared with the fingers, which makes it harder for your body's immune system to detect and eliminate the infection.

Nail fungus is more common among older adults for several reasons, including diminished blood circulation, more years of exposure to fungi and because nails may grow more slowly and thicken with aging, making them more susceptible to infection. Nail fungus also tends to affect men more than women and those with a family history of this infection. Resistance to fungal infection likely has a genetic component.

These factors also can increase your risk of developing nail fungus:

• Perspiring heavily
• Working in a humid or moist environment
• Wearing socks and shoes that hinder ventilation and don't absorb perspiration
• Walking barefoot in damp public places, such as swimming pools, gyms and shower rooms
• A minor skin or nail injury, a damaged nail or another infection
• Diabetes, circulation problems or a weakened immune system

Once a nail fungal infection begins, it can persist indefinitely if not treated. See your doctor at the first sign of nail fungus, which is often a tiny white or yellow spot under the tip of your nail.

Nail fungal infections can be painful and may cause permanent damage to your nails. They may also lead to other serious infections that can spread beyond your feet if you have a suppressed immune system due to medication, diabetes or other conditions.

Fungal infections of the nail pose the most serious health risk for people with diabetes and for those with weakened immune systems, such as people with leukemia or those who've had an organ transplant. If you have diabetes, your blood circulation and the nerve supply to your feet can become impaired. Therefore, any relatively minor injury to your feet — including a nail fungal infection — can lead to a more serious complication, requiring timely medical care. See your doctor immediately if you suspect nail fungus.

The first step to beating nail fungus is getting a diagnosis. Your doctor will likely examine your nails first. To test for fungi, your doctor may scrape some debris from under your nail for analysis.

The debris can be examined under a microscope or cultured in a lab to identify what's causing the infection. Other conditions, such as psoriasis, can mimic a fungal infection of the nail. Microorganisms, including yeast and bacteria, also can infect nails. Knowing the cause of your infection helps determine the best course of treatment.

Nail fungus can be difficult to treat, and repeated infections are common. Over-the-counter antifungal nail creams and ointments are available, but they aren't very effective.

Oral medications
To treat nail fungus, your doctor may prescribe an oral antifungal medication, such as:

• Itraconazole (Sporanox)
• Fluconazole (Diflucan)
• Terbinafine (Lamisil)

These medications help a new nail grow free of infection, slowly replacing the infected portion of your nail. You typically take these medications for six to 12 weeks but won't see the end result of treatment until the nail grows back completely. It may take four months or longer to eliminate an infection. Recurrent infections are possible, especially if you continue to expose your nails to warm, moist conditions.

Antifungal drugs may also cause side effects ranging from skin rashes to liver damage. Doctors may not recommend them for people with liver disease or congestive heart failure or for those taking certain medications.

Other treatment options
Your doctor may also suggest these nail fungus treatments:

• Antifungal lacquer. If you have a mild to moderate infection of nail fungus, your doctor may prefer to prescribe an antifungal nail polish called ciclopirox (Penlac). You paint it onto your infected nails and surrounding skin once a day. After seven days, you wipe the piled-on layers clean with alcohol and begin fresh applications. Daily use of Penlac for about one year has been shown to help clear nail fungal infections, but researchers found that it cured the infections in less than 10 percent of people using it.
• Topical medications. Your doctor may also opt for other topical antifungal medications. In some cases, you may be advised to use these creams with an over-the-counter lotion containing urea to help speed up absorption. Topical medications usually don't provide a cure, but may be used in conjunction with oral medications.

If your nail infection is severe or extremely painful, your doctor may suggest removing your nail. A new nail will usually grow in its place, though it will come in slowly and may take as long as a year to grow back completely.

To help prevent nail fungus and reduce recurrent infections, practice good hand and foot hygiene by following these steps:

• Keep your nails short, dry and clean. Trim nails straight across and file down thickened areas. Thoroughly dry your hands and feet, including between your toes, after bathing.
• Wear appropriate socks. Synthetic socks that wick away moisture may keep your feet dryer than do cotton or wool socks (you can also wear synthetic socks underneath other socks). Change them often, especially if your feet sweat excessively. Take your shoes off occasionally during the day and after exercise. Alternate closed-toe shoes with open-toed shoes.
• Use an antifungal spray or powder. Spray or sprinkle your feet and the insides of your shoes.
• Wear rubber gloves. This protects your hands from overexposure to water. Between uses, turn the rubber gloves inside out to dry.
• Don't trim or pick at the skin around your nails. This may give germs access to your skin and nails.
• Don't go barefoot in public places. Wear shoes around public pools, showers and locker rooms.
• Choose a reputable manicure and pedicure salon. Make sure the salon sterilizes its instruments. Better yet, bring your own.
• Give up nail polish and artificial nails. Although it may be tempting to hide nail fungal infections under a coat of pretty pink polish, this can trap unwanted moisture and worsen the infection.
• Wash your hands after touching an infected nail. Nail fungus can spread from nail to nail.

Sometimes, because current treatments can take a long time to work and aren't always effective, people turn to home remedies. Two remedies purported to help nail fungus infections are vinegar and Vicks VapoRub.

• Vinegar. While there's no direct evidence that a vinegar soak can cure nail fungus, some studies have shown that it can inhibit the growth of certain bacteria. Experts suggest soaking your feet for 15 to 20 minutes in a mixture of 1 part vinegar to 2 parts warm water. You can soak your feet like this daily. But if your skin becomes irritated, try soaking only two to three times a week, or increase the amount of water in the mixture.
• VapoRub. As with vinegar, there have been no controlled clinical trials to assess the effectiveness of Vicks VapoRub on nail fungus, but there have been numerous anecdotal reports that it works. However, there's no consensus on how often to apply this product, so check with your doctor before using this product in a way it wasn't designed to be used.