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Black Line on Nail: Causes, Treatment, and More

Jul 19, 2023Jul 19, 2023

Possible Causes Include Injury or Various Health Conditions

A black line on the nail could be normal, such as when it is just a color variation. Other possible causes range from injury or taking certain medications to various health conditions like human immunodeficiency virus (HIV) and melanoma.

Even though a black line on the nail could be something minor or normal, you shouldn’t ignore changes in your nails.

This article will dive into the details of each cause of a black line on the nail, plus explain other symptoms that may accompany it, diagnosis, treatment, and when to seek medical care.

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Black lines on a nail could mean many things. It may be a normal color variation, but other things can also cause it. These include injury, medication side effects, and health conditions.

Melanonychia is the most common cause of a black line on a nail. This condition is characterized by black or brown discoloration of the nail plate. It can affect just one nail or multiple nails on the fingers and toes. It accounts for nearly half of all cases of nail discoloration.

There are several types of melanonychia, each with its own common causes. These include:

While each has distinct causes, melanonychia happens when your skin overproduces melanin (skin pigment) or melanocytes (pigment cells).

When your nail endures trauma from a hit, pressure, or even nail biting, a splinter hemorrhage may result. This area of bleeding under the nail resembles a splinter (thus the name). These injuries run in the direction of nail growth (vertically).

Some medications can also cause a black line on the nail. These medications may include:

Of these, the most common cause of drug-related black lines on the nail is chemotherapy.

HIV can cause nail changes, including black lines on the nails. The virus itself may cause these nail changes, as can medicines used to treat HIV. If the black line on your nail is due to your medication, symptoms usually occur soon after you begin treatment.

Melanoma, a serious form of skin cancer, can cause a black line on the nail. According to the American Academy of Dermatology Association (AADA), the following are symptoms of melanoma of the nail:

The AADA recommends performing routine skin checks to look for any signs of skin cancer, including on and around your nails.

When black lines appear on multiple nails, it tends to point to a systemic (body-wide) cause rather than an injury. One example of a health condition that could lead to black lines on multiple nails is endocarditis, a bacterial infection in the heart.

Black lines on the nail occur with endocarditis due to damaged blood vessels. They are called splinter hemorrhages.

A fungal nail infection can also cause longitudinal melanonychia. While rare, Candida infection of the nail (a fungal infection caused by a yeast) can sometimes present with a black line. It can sometimes mimic melanoma. A fungal infection can be confirmed with a nail biopsy (taking a sample to examine in the lab) or culture.

Psoriasis (an autoimmune skin condition) can sometimes present with a black line on the nail. In addition, nail psoriasis can cause nails to split, lift away from the nail bed, and lead to itching and thickening. About 70% to 80% of people with psoriasis have it on their nails.

In addition to a black line on the nail, other symptoms may co-occur, depending on what is causing it. These symptoms may include:

Since so many factors can cause a black line on a nail, a healthcare provider will do a physical exam and take a thorough medical history. Be prepared to share the following:

Once a healthcare provider understands your symptoms and health history, they may be able to narrow down some possibilities. They may order diagnostic tests like a nail biopsy and blood tests to confirm their suspicions. If a healthcare provider suspects endocarditis, they may also order a chest X-ray, an electrocardiogram (ECG or EKG), or an echocardiogram.

Treatment of a black line on a nail depends on the cause. In many cases, your nail will not require treatment, and the black line will go away on its own.

However, the underlying condition needs to be addressed in the case of a health condition. In the case of medication, a healthcare provider may recommend discontinuing or changing your prescription. Do not adjust or stop your medications without consulting a healthcare provider.

Anytime you notice changes to your nails, especially without an apparent cause, like an injury, it's essential to get it checked out by a healthcare provider. This is especially true if you have other symptoms that could indicate a health condition.

Many things can cause black lines on nails, including infections, injury, health conditions, and medications. If a health condition causes the black line on your nail, you may also experience other symptoms that correlate with that health condition. Similarly, if medications cause it, you may notice other medication side effects.

A healthcare provider will do a physical exam and order some diagnostic tests to diagnose the black line on your nail. You may not need treatment, but if a health condition causes the black line on your nail, treatment involves addressing the underlying cause.

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National Library of Medicine. Splinter hemorrhages.

American Academy of Dermatology Association. How to check your nails for melanoma.

Usui S, Dainichi T, Kitoh A, Miyachi Y, Kabashima K. Janeway lesions and splinter hemorrhages in a patient with eosinophilic endomyocarditis. JAMA Dermatol. 2015;151(8):907-908. doi:10.1001/jamadermatol.2015.0388

Cohen PR, Shurman J. Fungal melanonychia as a solitary black linear vertical nail plate streak: case report and literature review of candida-associated longitudinal melanonychia striata. Cureus. 2021;13(4):e14248. doi:10.7759/cureus.14248

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By Kathi ValeiiAs a freelance writer, Kathi has experience writing both reported features and essays for national publications on the topics of healthcare, advocacy, and education. The bulk of her work centers on parenting, education, health, and social justice.