Dark Lines on Toenails: Causes, Melanoma & Diagnosis

A close-up of a toe with a large section of the toenail missing on one side, exposing the nail bed. The surrounding skin appears normal and healthy. Dark lines on the toenails are often seen in the office and asked about by patients. Although most cases of dark nails are benign melanin in the nail root, a small percentage may represent melanoma, a potentially fatal cancer. Pigmentary changes in nail appearance may occur from trauma, inflammatory disease, occupational exposure, fungal infections, etc.

Quick Answer

Dark lines on toenails can be caused by various factors, including benign melanin deposits, trauma, inflammatory disorders, or certain medications. While often harmless, a small percentage of these lines may indicate melanoma, an aggressive form of cancer that Seattle Foot and Ankle Center notes is mostly diagnosed between the ages of 40 and 70. Due to the potential for serious conditions like acral melanoma, it is crucial to seek professional evaluation from a podiatrist for any suspicious dark lines on toenails to rule out cancer.

The deposition of melanin, or dark lines in the nail plate, can be caused by:

• mole or birthmark in the nail root;
• dark spots in the nail root;
• nail tumors, such as squamous cell carcinoma;
• human immunodeficiency virus (HIV) infection;
• inflammatory nail disorders;
• trauma;
• pregnancy;
• medications;
• endocrine disorders, such as Addison’s disease and Cushing’s disease; and/or
• melanoma.

Acral melanoma tumors are an aggressive type of cancer and have a poorer survival outcome. It is the most common type of melanoma in dark-skinned individuals, and is mostly diagnosed between the ages of 40 and 70. This can be confused with ethnic or racial pigmentation, which, also in darker-skinned individuals, dark lines on the nails can commonly occur in one or multiple nails, and is mostly benign.

Read what the warning signs are for cancer with dark lines on toenails.

If you suspect that you have melanoma cancer according to either of the criteria above, please contact Dr. John Hoy at Seattle Foot and Ankle Center in Seattle, Washington, to discuss a biopsy procedure to rule out cancer.

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Frequently Asked Questions

1 What causes dark lines to appear on toenails?

Dark lines on toenails can result from various factors, including benign melanin deposits, trauma, inflammatory nail disorders, or certain medications. More serious causes, such as nail tumors or melanoma, are also possible.

2 How can I tell if a dark line on my toenail is serious, like melanoma?

While many dark lines are benign, a small percentage can indicate melanoma, an aggressive form of cancer. The page advises contacting a podiatrist for evaluation and a possible biopsy if you suspect melanoma, especially since acral melanoma can be confused with ethnic pigmentation.

3 When should I see a doctor for dark lines on my toenails?

You should seek medical evaluation if you suspect melanoma or are concerned about any changes in your toenails. A podiatrist can assess the cause of the dark lines and determine if a biopsy is needed to rule out serious conditions like cancer.

4 What is a biopsy, and why might it be needed for dark toenail lines?

A biopsy is a medical procedure where a small tissue sample is taken for examination under a microscope. It may be needed for dark toenail lines to accurately diagnose the cause, particularly to differentiate between benign pigmentary changes and more serious conditions like melanoma.

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Frequently Asked Questions