Fungal Nail Infection (Onychomycosis)
A common fungal infection of the nails
Quick Facts
- Type: Fungal infection
- Common site: Toenails (more than fingernails)
- Main signs: Thick, discolored, brittle nails
- Treatment: Antifungal medication
Overview
A fungal nail infection, known medically as onychomycosis, is an infection of the nail caused by fungi. It most often affects the toenails, particularly the big toe, but fingernails can also be involved. The infection makes the nail thickened, discolored, brittle, and sometimes distorted in shape.
Fungal nail infections are very common and tend to develop slowly. While they are usually not dangerous, they can be persistent, hard to clear, and cosmetically bothersome. In some people, especially those with diabetes or a weakened immune system, a fungal nail infection can lead to more serious foot problems, so treatment may be more important. The same fungi that cause athlete's foot frequently cause nail infections.
Symptoms
A fungal nail infection usually develops gradually and may affect one or several nails. Common signs include:
- Thickening of the nail
- Discoloration, often white, yellow, or brown
- Brittle, crumbly, or ragged nail edges
- A distorted or misshapen nail
- Debris building up under the nail
- The nail lifting away from the nail bed
- A slightly unpleasant odor in some cases
The infection is often painless at first but can become uncomfortable or make walking and wearing shoes difficult as the nail thickens. It frequently occurs alongside athlete's foot.
Causes
Fungal nail infections are caused by various fungi, most commonly the same dermatophyte fungi that cause athlete's foot and ringworm; yeasts and molds can also be responsible. These fungi thrive in warm, moist environments and enter the nail through small cracks or separations between the nail and the skin. Contributing factors include:
- Walking barefoot in damp communal areas such as locker rooms, pools, and showers
- Sweaty feet and tight, non-breathable footwear
- Existing athlete's foot that spreads to the nails
- Minor nail or skin injuries that allow fungi to enter
Once established, the fungus grows slowly within the nail, which is why infections can take a long time to clear.
Risk Factors
You are more likely to develop a fungal nail infection if you:
- Are older, as nails grow more slowly and infections are more common with age
- Have athlete's foot
- Sweat heavily or wear closed, non-breathable shoes for long periods
- Use public pools, showers, or locker rooms barefoot
- Have diabetes, poor circulation, or a weakened immune system
- Have a nail injury or other nail conditions, such as psoriasis
- Have a family history of fungal nail infections
Diagnosis
A clinician may suspect a fungal nail infection from its appearance, but because other conditions can look similar, confirming the diagnosis is often recommended before starting long courses of treatment. Methods include:
- Taking nail clippings or scrapings to examine under a microscope
- Sending a sample to a laboratory for fungal culture or other tests to identify the organism
Confirmation is helpful because conditions such as nail psoriasis, injury, and other nail disorders can mimic a fungal infection, and antifungal treatment will not help those. Identifying the type of fungus can also guide the choice of medication.
Treatment
Fungal nail infections can be stubborn, and treatment often takes several months because the nail must grow out. Options include:
- Oral antifungal medications: Usually the most effective treatment, taken for several weeks to months; these may require monitoring and are chosen based on health conditions and other medications.
- Topical antifungal treatments: Medicated nail lacquers or solutions applied to the nail, often used for milder infections or when oral medication is not suitable, though they are generally less effective.
- Nail debridement: Trimming and thinning the thickened nail to reduce discomfort and help treatment.
- Other approaches: In some cases, partial or complete removal of a severely affected nail.
Even with successful treatment, infections can return, so good foot and nail care afterward is important.
Prevention
You can lower the risk of fungal nail infections and reduce recurrences by:
- Keeping feet clean and thoroughly drying them, especially between the toes
- Wearing breathable footwear and moisture-wicking socks, and changing socks if feet sweat
- Wearing sandals or shower shoes in communal showers, pools, and locker rooms
- Treating athlete's foot promptly
- Keeping nails trimmed straight and not too short, and using clean nail tools
- Avoiding sharing shoes, socks, and nail clippers
- Disinfecting or replacing shoes that may harbor fungus
When to See a Doctor
See a healthcare provider if a nail is thickening, discolored, or distorted and home care does not help, or if you want to confirm the diagnosis before treatment. Many over-the-counter products are ineffective for true nail infections, so professional advice is useful.
It is especially important to see a doctor if you have diabetes, poor circulation, or a weakened immune system, since fungal nail infections can lead to more serious foot infections in these situations. Seek prompt care for any foot redness, swelling, pain, or signs of a spreading infection.
Frequently Asked Questions
What does a fungal nail infection look like?
It typically makes the nail thick, discolored (white, yellow, or brown), brittle, and sometimes distorted, with debris under the nail. It is most common in the toenails, especially the big toe.
What causes nail fungus?
It is caused by fungi, most often the same ones that cause athlete's foot. They thrive in warm, moist conditions and enter through small cracks in the nail, especially with sweaty feet, tight shoes, or barefoot use of communal showers.
How is a fungal nail infection treated?
Treatment usually involves oral antifungal medication taken for weeks to months, sometimes with topical antifungals and trimming of the thickened nail. Because the nail must grow out, clearing the infection takes time.
Why is it so hard to get rid of?
The fungus grows slowly inside the nail, which itself grows slowly, so it can take many months to clear and may return afterward. Confirming the diagnosis and using effective medication improve the chances of success.
When should I see a doctor?
See a doctor if home care is not working or to confirm the diagnosis, and especially if you have diabetes, poor circulation, or a weak immune system, since nail infections can lead to more serious foot infections in these cases.
References
- American Academy of Dermatology.
- Mayo Clinic. Nail fungus.
- MedlinePlus, U.S. National Library of Medicine.