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“Longitudinal Melanonychia is the medical term for a dark, hyperpigmented streak that appears on a nail,” explains Dr. Adam Mamelak, a board certified Dermatologist and skin cancer specialist at Sanova Dermatology. “Basically, it represents an accumulation of melanin pigment in the cells in the nail beds. As the hard nail plate grows, it picks up this pigment and forms a streak.”
In 73% of cases in adults, it’s simply due to already-present cells producing more pigment than needed and causing a solid stripe the length of the nail bed. “For example, if a patient has a benign mole in the skin adjacent to the nail, and a few of the mole cells with their pigment grow into the nail bed, this streak can result.” Longitudinal melanonychia can in fact result from a variety of sources, from system-wide syndromes to localized trauma, but most of these are completely benign.
Commonly, those with longitudinal melanonychia will see a dark stripe, usually black or brown, that runs the length of the nail bed, either on their hands or feet.
The condition is much more common in African Americans and those with naturally dark skin, though it’s possible for anyone to develop.
There are many causes for longitudinal melanonychia. “It can appear in a variety of syndromes, with infections, or as the result of trauma to the nail,” says Dr. Mamelak. If you are naturally dark-skinned, you will likely have a higher chance of developing these linear streaks on your nails, especially on ones used to hold and grasp things often, such as the index finger and thumb.
While most of these cases are completely benign, a small number of people who have longitudinal melanonychia also have subungual melanoma or melanocytic hyperplasia. While these cases are rare, if the stripe occurs along the length of the nail plate, exhibits blurred edges, and is confined to a single digit such as the index finger, thumb, or big toe, it may be a good idea to have it checked by a board-certified dermatologist.
For more information on longitudinal melanonychia or to have a nail stripe checked by one of our dermatologists, please contact us.