Table of ContentsView AllTable of ContentsTypesCommon CausesNon-CancerousCancerEnvironmentalGeneticWhat to Do
Table of ContentsView All
View All
Table of Contents
Types
Common Causes
Non-Cancerous
Cancer
Environmental
Genetic
What to Do
A brown line on the nail is calledlongitudinal melanonychiaorlongitudinal striata. It is the most common type of melanonychia, a medical word for ablack or brownish pigmentation of the nail plate(the hard part oftoenails or fingernails).
Longitudinal melanonychia can have many causes, from harmless pigment deposits or growths to infections, body-wide diseases, or melanoma (skincancer).
This article will cover the causes of longitudinal melanonychia, what happens in nail cells that cause the black or brown lines, the symptoms of melanonychia, as well as how the nail condition is diagnosed and treated.
Rytis Bernotas / Getty Images
Types of Longitudinal Melanonychia
What Is Transverse Melanonychia?Transverse melanonychia is like longitudinal melanonychia except the lines go side to side (transverse) across the nail instead of up and down (longitudinal). It is a rare type and is mostly associated with certain medications and radiation therapy for cancer.
What Is Transverse Melanonychia?
Transverse melanonychia is like longitudinal melanonychia except the lines go side to side (transverse) across the nail instead of up and down (longitudinal). It is a rare type and is mostly associated with certain medications and radiation therapy for cancer.
Melanonychia striata can look like apartial or complete striperunning length-wise (longitudinal) along the nail. Causes of longitudinal melanonychia are categorized according to how they happen:
Each type can have a range of causes:
Melanocytic Activation
Traumatic or infectious causes:
Medical condition-related causes:
Health-related causes:
Treatment-related causes:
Melanocytic Hyperplasia
Should I Worry About Melanonychia?The main concern with the melanocytic hyperplasia type is that when melanocytes copy themselves, there can be errors in the genes. These errors may lead the cells to eventually become cancerous (neoplasms).
Should I Worry About Melanonychia?
The main concern with the melanocytic hyperplasia type is that when melanocytes copy themselves, there can be errors in the genes. These errors may lead the cells to eventually become cancerous (neoplasms).
What Are Common Toenail Problems and How Are They Treated?
Common Causes and Risk Factors
Many common causes of longitudinal melanonychia are related to the extra production of melanin.
Melanin in the nail plate is usually evenly spread out, but it can become irregular. With longitudinal melanonychia, pigment cells at the bottom of the nail transfer melanin to nail cells. As the nail grows out, the melanin gets carried with it, creating length-wise stripes from the nail fold (cuticle).
Many causes of the brown lines on the nails are harmless and nothing to worry about. However, some of the causes are serious and need medical attention.
Nail Trauma
Nail trauma (especially starting on or near the base of the nail) and blood under the nail (subungual hematomas) are common causes of longitudinal melanonychia.
For example, hitting your nail with a hammer could cause blood to pool under it and “turn on” the melanocytes in the nail bed.
When this happens, melanin will collect in the nail cells and cause blackish or grayish discoloration. This process is a type of melanocyte activation. It’s similar to why freckles get darker when ultraviolet (UV) rays from the sun activate melanocytes in the skin.
Infections
Fungal, viral, or bacterial infections can also cause streaks on the nails.
Yellow Nails
Autoimmune and Skin Conditions
Skin and nail conditions can cause longitudinal melanonychia. Autoimmune disorders can also cause nail discoloration.
Benign Growths
When nail cells multiply abnormally, it is often not cancerous. Common benign growths that can cause longitudinal melanonychia include:
How to Tell if the Cause Is Benign
Longitudinal melanonychia that’s not cancer is typically light to dark brown stripes. The lines are parallel and regular in color, thickness, and spacing. The border will be clearly defined and less than 3 millimeters (mm) in width—roughly 1/10th of an inch.
Longitudinal Melanonychia in ChildrenThe prevalence of melanonychia is about 1% of people of any age, but it’s extremely rare in children. More than 50 years of research suggests that just 16 cases of melanonychia have been documented in children and they were diagnosed as melanoma cancer.There are differences in how melanonychia looks in adults compared to how it looks in children. If you are concerned about changes to your child’s nails, it’s important to have their provider take a look.
Longitudinal Melanonychia in Children
The prevalence of melanonychia is about 1% of people of any age, but it’s extremely rare in children. More than 50 years of research suggests that just 16 cases of melanonychia have been documented in children and they were diagnosed as melanoma cancer.There are differences in how melanonychia looks in adults compared to how it looks in children. If you are concerned about changes to your child’s nails, it’s important to have their provider take a look.
The prevalence of melanonychia is about 1% of people of any age, but it’s extremely rare in children. More than 50 years of research suggests that just 16 cases of melanonychia have been documented in children and they were diagnosed as melanoma cancer.
There are differences in how melanonychia looks in adults compared to how it looks in children. If you are concerned about changes to your child’s nails, it’s important to have their provider take a look.
Causes of a Loose Toenail or Fingernail
Sometimes the growths that cause longitudinal melanonychia are cancerous or could become cancerous.
Caring for Your Nails During Chemotherapy
Nail Apparatus Melanoma
Melanoma accounts for about 1% of skin cancers, but it is also the most dangerous.
ABCDEs of MelanomaIf you’re worried that a change on your skin or nails could be cancer, it may help to know the ABCDEs of melanoma:Asymmetry:One side of the area is bigger than the other or not shaped the same on both sides.Border:The area has an irregular border around it.Color:The area is a range of colors from white to brown to black, or even flesh-colored.Diameter:The area is about the size of a pencil’s eraser or larger (6 cm); however, cancerous spots can be smaller earlier in the disease.Evolving:The area is changing size, shape, or color.
ABCDEs of Melanoma
If you’re worried that a change on your skin or nails could be cancer, it may help to know the ABCDEs of melanoma:Asymmetry:One side of the area is bigger than the other or not shaped the same on both sides.Border:The area has an irregular border around it.Color:The area is a range of colors from white to brown to black, or even flesh-colored.Diameter:The area is about the size of a pencil’s eraser or larger (6 cm); however, cancerous spots can be smaller earlier in the disease.Evolving:The area is changing size, shape, or color.
If you’re worried that a change on your skin or nails could be cancer, it may help to know the ABCDEs of melanoma:
Nail apparatus melanoma (subungual melanoma) is a rare subtype ofacral lentiginous melanomathat accounts for only 0.7% to 3.5% of all melanoma skin cancers. While melanoma cannot be “cured,” studies have shown that treatment often leads to a good outlook for patients. Usually, it requires surgery to remove the cancer.
When doing a physical examination of your nail, a provider will look for certain telltale signs of cancer:
Subungual melanoma usually involves a single finger or toe rather than more than one. Other symptoms include lengthwise streaks on the affected digit and darkening of the palms of the hands or soles of the feet.
DermNet /CC BY-NC-ND
Hutchinson’s sign is a key indicator of subungual melanoma. This happens when a streak goes 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. Your provider may take a small sample of your nail and the tissue underneath to be checked in a lab. If a problem like cancer is found, early diagnosis and treatment lead to better outcomes.
Environmental Causes
Examples of pigments that can get absorbed include:
If the cause is environmental, the streak will usually not go far past the whitish crescent at the base of the nail (lunula). There can also be discoloration beneath the nail fold and the surrounding rim of the skin.
Carefully looking at your cuticles and reviewing your medical history can help a healthcare provider identify environmental causes of melanocytosis.
What Nutritional Deficiency Causes Brown Lines on Nails?Malnutrition can cause changes to your skin and nails. A brown line on your nails can be related to not having enough of certain nutrients in your diet, including vitamin B12 and folate.
What Nutritional Deficiency Causes Brown Lines on Nails?
Malnutrition can cause changes to your skin and nails. A brown line on your nails can be related to not having enough of certain nutrients in your diet, including vitamin B12 and folate.
Common Salon Nail Infections
Genetic Causes
Longitudinal melanocytosis can occur with several rare genetic disorders in which skin hyperpigmentation (excess pigmentation) is a common symptom.
Genetic disorders occur because you have certain mutations in your genes. 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:
Having brown lines on your nails is not always a problem, but if you’re worried about the discoloration, it’s important to tell your provider. There are many causes of longitudinal melanonychia, and you won’t know whether or not it needs to be treated until you see a provider who can tell you why you have it.
If the reason for the lines is something harmless, you may not need to do anything other than keep an eye on your nails to make sure they don’t change in other ways. If there’s a specific cause that can be treated (like a skin disorder or cancer), your provider will discuss next steps.
Summary
A darkened streak on the nail bed does not necessarily mean that you have a disease, but if it’s persistent, affects a large part of a nail, or is associated with bleeding, you should have your provider take a look. Many of the more serious conditions that can cause a brown line on your nail can be treated, but it’s important to be diagnosed early.
13 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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