Tinea nigra is a very rare fungal infection. It causes dark spots on the bottom of the feet, the palms of the hand, or, on rare occasions, the torso. These may be black or brown.
A type of yeast called Hortaea werneckii causes most tinea nigra infections. A person can get the infection when the yeast gets into their body, often through a small wound.
Keep reading to learn more about a tinea nigra infection, including the symptoms, diagnosis, and treatment options.
Tinea nigra causes brown or black patches to appear on the soles of the feet or the palms of the hand. The patches may be so small and faint that a person does not notice them. They also tend to grow slowly. The most common symptoms include:
- a patch on the foot or hand following an injury
- a single round, linear, or irregularly shaped patch that grows slowly
- growing patches that either cause no symptoms or itch
- patches that resemble a growing mole or freckle
- a slow growing brown patch on the torso
The infection affects people who live in tropical regions and those who have recently traveled to these areas.
Most people with tinea nigra have just one lesion. However, if the fungus comes into contact with multiple points of entry, such as wounds on both hands, a person may have several patches.
In healthy people, tinea nigra lives only on the superficial layers of the skin. It does not spread, cause serious infections, or present major health risks. It is more likely to affect young people under the age of 20 years.
Tinea nigra is a fungal infection, which means that a person gets it when they come into contact with a fungus that can cause the infection.
Scientists used to call Hortaea werneckii either Cladosporium werneckii, Exophiala werneckii, or Phaeoannellomyces werneckii. Another yeast called Stenella araguata may cause some cases of tinea nigra.
As with many other fungi, Hortaea werneckii thrives in moist or humid environments. It lives on dead and decaying organic material, such as soil and wood. It can get into the human body when it comes into contact with the skin, usually through a wound. It is most likely to live on parts of the body with many sweat glands, such as the hands and feet.
Certain risk factors increase a person’s likelihood of developing this infection. They include:
- living in a tropical or subtropical region
- recent travel to a subtropical or tropical region
- a history of hyperhidrosis, a condition that causes excessive sweating
- a recent injury
- contact with wood, soil, or compost, such as from gardening without gloves or woodworking in a tropical or subtropical region
In many cases, a person’s symptoms may lead a doctor to suspect tinea nigra. However, as tinea nigra can resemble the symptoms of several other conditions, it is important to get an accurate diagnosis.
The doctor may ask the individual about their recent travel, injury history, and exposure to wood, compost, or soil. They will also usually take a culture of the skin and send it to a lab to see whether Hortaea werneckii grows within a week. If it does, this means that the test is positive for tinea nigra.
Sometimes, a doctor may also perform a skin biopsy to test for skin cancer, as certain types of skin cancer can look similar to tinea nigra.
People who wish to try home remedies may see improvements with keratolytic agents. A keratolytic is a chemical that helps remove excess skin. Some potentially effective keratolytics include:
- wart cream
- salicylic acid
- Whitfield’s ointment
These drugs may not be safe during pregnancy, so women who are pregnant or trying to become pregnant should see a doctor instead of trying home remedies.
If home treatment fails, it is best to see a doctor. There are other possible causes of brown lesions on the skin.
Doctors usually prescribe topical antifungal creams to treat tinea nigra. People should apply the cream directly to the patch exactly as a doctor advises.
In some cases, a person may also need to take oral antifungal drugs, especially if the lesions are very large or if antifungal creams have not worked. However, oral drugs may not be effective.
Doctors do not know what treatment duration is optimal, but the authors of one report suggest that 1 month of treatment is sufficient.
People can reduce the risk of tinea nigra infections by protecting the skin from exposure to soil, compost, and other materials in which the Hortaea werneckii fungus likes to grow. Following this advice is especially important for people who travel to or live in tropical regions.
These strategies can help:
- practicing frequent handwashing, especially after spending time outside
- wearing gloves or other protective gear in the garden
- refraining from walking outside with bare feet
- wearing socks or shoes in public places
- changing socks frequently, especially if they get wet
- covering any wounds on the hands or feet before spending time outside
Several other skin conditions may look similar to tinea nigra. Other fungal infections, such as athlete’s foot, may also cause skin lesions, but they are not usually brown.
Melanoma, a type of skin cancer, can be deadly. It may also look very similar to tinea nigra in the early stages. Similarly to tinea nigra, melanoma is not typically painful at first. Therefore, people who do not get relief from home or medical treatment should see a dermatologist and request a biopsy.
Some other medical conditions and factors that may cause brown patches include:
- skin staining from henna
- skin hyperpigmentation from pregnancy or Addison’s disease
- complications of syphilis
- exposure to certain chemicals, such as silver nitrate
Tinea nigra is not a serious medical condition. Most people do not notice any symptoms other than brown spots on the skin.
However, as tinea nigra looks similar to several other conditions, it is important to see a doctor for an accurate diagnosis.
Prompt treatment can prevent serious skin-related conditions from getting worse.