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Black toenails can be unsightly and sometimes painful. While there are several potential causes of black toenails, many are easy to treat or may clear up on their own.

In this article, we look at six potential causes of a black toenail, in addition to treatment options and tips for prevention.

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There are various reasons for black toenails and many causes are easy to treat.

The cause of a black toenail may be benign or quite serious.

It is important for a person who develops a black toenail to understand some of the potential causes.

When in doubt, it is a good idea to be examined by a medical professional who can diagnose the problem and develop an effective treatment plan.

1. Repetitive trauma

When a person wears poorly-fitting shoes, they may be at risk of developing black toenails due to repetitive trauma.

Long-term pressure on the toes from poorly-fitting shoes can cause a range of problems, from small blisters to bloody blisters under the nail.

In mild cases, the black toenail will grow out naturally over time without treatment. In severe cases, such as when the nail begins to detach from the nail bed, a person should seek medical treatment.

2. Blunt force

In some cases, the trauma may be a one-time blunt-force injury, for example, if a person drops a heavy object on their foot or toes. When this happens, blood vessels in the nail bed break, causing blood to pool there.

The injured toe will start to hurt and pool blood beneath the skin almost immediately. The buildup of blood will cause the toe to feel painful and swollen. A doctor can treat this condition by draining the blood with a pinprick.

3. Fungal infections

Fungal infections are another common problem that can cause black toenails to form. Typically, a fungal infection causes a white or yellowish discoloration. However, debris can build up near the infection, causing the nail to appear black.

Toenails are particularly susceptible to fungal infections, as socks and shoes can provide a warm and moist breeding ground for a fungus to become established. Fungal infections can usually be prevented with proper foot care.

4. Melanoma

In rare cases, a black toenail may be caused by melanoma. Melanoma is the most aggressive form of skin cancer.

Melanoma causes the skin to develop one or more patches of dark, irregular-looking skin. In some cases, the patch of darkening skin grows beneath the nail bed.

Melanoma develops slowly, and without other symptoms, so it is often not noticed in the early stages, especially if it originates under the toenail.

5. Pigmentation changes

People's skin tones can naturally change over time. For people with darker skin, a dark patch may develop beneath the toenails.

Pigmentation changes are usually uniform, so if it affects a toe on one foot, it will usually affect the matching toe on the other foot. The fingernails may develop darker patches beneath them as well.

6. Underlying conditions

There are a few medical conditions that may cause black toenails, including:

In most cases, controlling the underlying condition will help the nail to regain its original color.

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Black toe nails may be a result of repetitive trauma from wearing poorly-fitting shoes.

Treatment for black toenails will vary depending on the cause.

In cases of blunt force injury, a doctor may make a small hole in the nail using a needle. This hole will allow the blood to drain and alleviate a lot of the pressure that has built up over time.

In more severe cases where an infection has developed, a doctor may need to prescribe additional medication to help the injury heal.

If a person has a repetitive injury, such as from wearing poorly-fitting shoes, it is likely a doctor will recommend resting the foot and switching shoes.

Underlying conditions such as diabetes will need to be treated first by a doctor, who may also adjust someone's regular treatment regime.

A person may be able to treat a fungal infection at home. Creams and ointments can be enough to kill the fungus and allow the nail to heal. These are available for purchase over the counter and online. However, if the infection does not go away after a few days, a person should consult a doctor.

In cases where the black toenail is found to be cancerous, a doctor will review all the treatment options available.

Preventing black toenails from forming is not always possible. However, there are many steps a person can take to reduce their risk of developing black toenails.

These steps include:

  • wearing sunblock and avoiding overexposure to UV rays
  • wearing properly fitted shoes
  • wearing proper footwear at the gym and work
  • wearing proper footwear when using a public shower
  • treating underlying medical conditions

A person should see a doctor if they experience a sudden, unexplainable black toenail, or if it does not heal with time and at-home treatments.

In cases of trauma or injury, the discolored part of the nail will disappear as the nail grows out.

Fungal infections can usually be treated at home and may not require a doctor's diagnosis.

Black toenails do not typically cause further problems for someone when they are the result of trauma or pigment discoloration.

When treated properly, fungal infections will also not cause any more problems. However, if left untreated, fungal infections may spread to other parts of the foot and body.

If a person is diagnosed with melanoma, they may receive a variety of cancer treatments, depending on the stage and severity of the disease.

In most cases, black toenails are relatively harmless, require minimal treatment, and do not cause any additional problems.