Foot Health Toenail Problems Causes and Risk Factors of Longitudinal Melanonychia Nail streaks may be a sign of injury, disease, or cancer By Susan J. Huang, MD Susan J. Huang, MD Facebook Twitter Susan Huang, MD, FAAD, is a board-certified dermatologist practicing at Sutter Health. She is also an instructor at Harvard Medical School. Learn about our editorial process Updated on January 17, 2022 Medically reviewed Verywell Health articles are reviewed by board-certified physicians and healthcare professionals. These medical reviewers confirm the content is thorough and accurate, reflecting the latest evidence-based research. Content is reviewed before publication and upon substantial updates. Learn more. by Kashif J. Piracha, MD Medically reviewed by Kashif J. Piracha, MD LinkedIn Kashif J. Piracha, MD, is board-certified in internal medicine and nephrology. He has an active clinical practice at Methodist Willowbrook Hospital in Houston, Texas. Learn about our Medical Expert Board Print Table of Contents View All Table of Contents Types Common Causes Benign Growths Genetics Cancer Environmental Causes Longitudinal melanonychia is the most common type of melanonychia, a medical term used to describe a black or brownish pigmentation of the nail plate (the hard part of toenails or fingernails). Longitudinal melanonychia can look like a partial or complete stripe running length-wise (longitudinal) along the nail. It can have many causes that range from harmless pigment deposits or growths to infections, body-wide diseases, or cancer. This article will explore the many causes of longitudinal melanonychia, what happens in nail cells, and how it's diagnosed. An Overview of Common Nail Problems Types of Longitudinal Melanonychia The color of your nails, hair, and skin are produced by cells known as melanocytes that produce a pigment called melanin. Cases of longitudinal melanonychia can divided based on how they occur: Melanocytic activation: Melanocytes produce extra melanin.Melanocytic hyperplasia: Melanocytes multiply abnormally. Melanocytic hyperplasia is especially concerning given that melanocytes are prone to genetic errors when they multiply. This can lead to the development of benign (noncancerous) or cancerous skin growths known as neoplasms. Recap Longitudinal melanoychia can be due to an excess production of a pigment called melanin or an overgrowth of pigment cells called melanocytes. Common Causes and Risk Factors Many common causes of longitudinal melanonychia are due to extra production of melanin. Although the melanin in the nail plate is generally evenly distributed, it can sometimes become irregular. With longitudinal melanonychia, pigment cells at the base of the nail will transfer melanin to nail cells. As the nail grows outward, the melanin will be carried along, creating length-wise stripes from the nail fold, or cuticle. There are many reasons why this might occur, some of which are totally harmless. Longitudinal melanonychia due to excess melanin is most common in people of African descent. It can also occur with nail trauma, body-wide disease, or nail infections. The cause of melanonychia can be usually diagnosed by a dermatologist, a physician who specializes in treating skin, hair, and nails. Rytis Bernotas / Getty Images Nail Trauma Nail trauma, especially starting on or near the base of the nail, and subungual hematomas, or blood under the nail, are common causes of longitudinal melanonychia. For example, if you hit your nail with a hammer, it can not only cause a bad bruise from a collection of blood, but also "turn on" melanocytes in the nail bed. When this happens, melanin will collect in the nail cells, causing blackish or grayish discoloration. This process is a type of melanocyte activation. It is not unlike how freckles darken when ultraviolet (UV) rays from the sun activate melanocytes in the skin. Infections Fungal, viral, or bacterial infections can also cause the streaks. These include: Subungual verruca, a wart under the nail plate that is caused by a virus Onychomycosis, a common fungal nail infection Chronic paronychia, a bacterial or fungal infection occurring where the side of a nail meets the skin Autoimmune and Skin Conditions Conditions that affect the skin and nails can cause longitudinal melanonychia. Autoimmune disorders, in which the immune system attacks the body's own tissues, can as well. These conditions include: Nail psoriasis, an autoimmune disorder that causes nail changes Addison's disease, an insufficiency of the adrenal glands caused by autoimmune disease, cancer, infection, or pituitary tumors (growths in the pituitary gland) Lichen planus, an inflammatory skin condition that may be caused by an autoimmune reaction Recap Longitudinal melanonychia from excess melanin can be caused by nail injuries, infections, and autoimmune conditions. It commonly occurs in people of African descent. Benign Growths When nail cells multiply abnormally it is often noncancerous. Common types of benign growths that can cause longitudinal melanonychia include: Pyenic granuloma, which are blood-red skin growths that sometimes occur in pregnancy or as a side effect of certain drugsSubungual exostosis, a bony overgrowth of the fingertips or toes, possibly caused by persistent bone irritationMyxoid cysts, or small, benign lumps that occur near a nail How to Tell If the Cause Is Benign Non-cancerous longitudinal melanonychia typically has the appearance of light to dark brown stripes that are parallel and regular in color, thickness, and spacing. The border will be clearly defined and less than 3 millimeters (mm) in width, or roughly 1/10th of an inch. Longitudinal melanonychia is extremely rare in children. When it does occur, 77.5% will be the result of a benign growth. Another sign that longitudinal melanonychia is benign is the yellowish fading of color along the outer edges of the stripe. Melanonychia caused by a serious disease doesn't typically fade. Moreover, if a blackish mark is caused by an injury, it will tend to move toward the tip as it grows, leaving behind an unblemished nail. Recap Streaks caused by noncancerous growths tend to have a regular color, thickness, and spacing with a well-defined border that's less than 3 mm in width. However, it's important to have it checked by a healthcare provider. Causes of a Loose Toenail or Fingernail Genetic Causes Longitudinal melanocytosis can occur with several rare genetic disorders in which skin hyperpigmentation (excess pigmentation) is a common symptom. Genetic disorders occur due to genes within your cells. Many of these conditions are autosomal dominant, meaning that you only need to inherit the gene mutation from one parent to have the disease. Examples of genetic causes include: Familial amyloidosis, a rare and potentially life-threatening disease that occurs when a protein called amyloid builds up in organs and tissuesLaugier-Hunziker syndrome, a rare disorder with hyperpigmentation of the mouth, lips, fingers, and nails as well as the high risk of cancerPeutz-Jeghers syndrome, a rare disorder that leads to benign polyps in the gastrointestinal tract and hyperpigmented lesions on the mouth, lips, nails, and fingersTouraine syndrome, a rare, non-progressive disorder characterized by sparse body hair, brittle teeth, a reduced ability to sweat, and hyperpigmented lesions Cancer Sometimes the neoplasms, or growths, that cause longitudinal melanonychia are cancerous or potentially cancerous. This can include: Subungual melanoma, a dangerous form of skin cancer occurring under the nail plate Glomus tumor, a rare and potentially deadly tumor found mainly under the nail, on the fingertip, or at the end of a toe Keratoacanthoma—a low-grade, dome-shaped tumor usually found on sun-exposed skin—can also cause longitudinal melanonychia. The cause of keratoacanthoma is unknown, but it's often considered a type of squamous cell carcinoma, a type of skin cancer. Transverse melanonychia is a rare form of melanoychia in which a darkened line runs side to side along the nail plate. It is typically associated with certain medications and radiation therapy used to treat cancer. Caring for Your Nails During Chemotherapy Subungual Melanoma Melanoma accounts for about 1% of skin cancers, but it is also the most dangerous. Subungual melanoma, also called nail matrix melanoma, is a type that mainly affects people over 50 and is considered rare, accounting for only 0.7% to 3.5% of all melanoma skin cancers. When performing a physical examination of the nail, the doctor will look for certain tell-tale signs of cancer: Involvement of more than two-thirds of the nail plate Grey or black colors mixed with brownIrregular brown and granular pigmentationVariations in the color and thickness of the stripeBlurred borders larger than 3 mmDistortion of the nail plateRecurrent, spontaneous bleeding at the same site Subungual melanoma more often involves a single finger or toe rather than several. Other symptoms may include lengthwise streaks on the affected digit as well as the darkening of the palms or soles. Hutchinson's sign is one of the key indications of subungual melanoma. This is when a streak extends from the tip of the nail all the way down to the nail bed and into the cuticle. Subungual melanoma can only be diagnosed with a nail biopsy. If there are suspicious signs, your healthcare provider may take a small sample of the nail for evaluation in the lab. If a problem is found, early diagnosis and treatment leads to better outcomes. DermNet / CC BY-NC-ND Recap Rare genetic disorders and rare but serious forms of skin cancer can cause longitudinal melanonychia. A nail sample is needed to diagnose cancer. Environmental Causes Longitudinal melanonychia can also develop when pigments other than melanin are introduced into the nail fold. These can be absorbed by the cuticle and underlying nail cells and be carried along as the nail plate grows. Examples include: InkTar deposits from smokingHair dyes or henna inkSilver nitrate used to heal burns and woundsPotassium permanganate, which is a disinfectant sometimes applied to skin If the cause is environmental, the streak will usually not go far past the lunula, which is the whitish crescent at the base of the nail. There may also be discoloration beneath the nail fold and the surrounding rim of skin. An examination of the cuticle along with a review of the medical history can help a healthcare provider identify environmental causes. Recap Other types of pigments from dyes, inks, or wound treatments can also cause a stripe on the nail. Common Salon Nail Infections Summary Longitudinal melanonychia can result from an overproduction of melanin (skin pigment) or an increase in melanocytes (pigment cells). These increases in melanin or melanocytes can occur for many reasons ranging from harmless growths to injuries, infections, or cancer. A Word From Verywell The appearance of a darkened streak on the nail bed can be distressing, but it is doesn't necessarily mean that you have a disease or are at risk of illness. At the same time, it isn't something you should ignore, particularly if the condition is persistent, affects a large part of a nail, or is associated with bleeding. Have it looked at by a healthcare provider. An early diagnosis can make a big difference if it due to a serious condition. Was this page helpful? Thanks for your feedback! Sign up for our Health Tip of the Day newsletter, and receive daily tips that will help you live your healthiest life. Sign Up You're in! Thank you, {{form.email}}, for signing up. There was an error. Please try again. What are your concerns? Other Inaccurate Hard to Understand Submit 10 Sources Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. Güneş P, Göktay F. Melanocytic lesions of the nail unit. Dermatopathology (Basel). 2018;5(3):98-107. doi:10.1159/000490557 Khan K, Mavanur AA. Longitudinal melanonychia. BMJ Case Rep. 2015;2015:bcr2015213459. doi:10.1136/bcr-2015-213459 Jefferson J, Rich P. Melanonychia. 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