A Brown Line Under Your Nail: Your Body Might Be Trying to Tell You Something

It started as a dark spot under a toenail, the kind of thing almost anyone would blame on a sports knock. The man who ignored it was one of the most famous musicians in the world. A brown or black stripe under the nail can be a sign of subungual melanoma, a rare but serious form of skin cancer. Still, not every change is a reason to panic, and most dark lines turn out to be completely harmless.

The Story That Put Nail Melanoma on the Map

In 1977, reggae legend Bob Marley noticed a dark spot under his toenail and, as a passionate football player, assumed it was simply an injury from the pitch. The spot turned out to be acral lentiginous melanoma, a rare subtype of skin cancer that can appear on the palms, the soles and under the nails. Marley died in 1981 at the age of 36. His story is still used by dermatologists today, including at the University of Colorado Cancer Center and by the AIM at Melanoma Foundation, as a reminder that this type of melanoma does not always look the way people expect, and that it is not mainly linked to sun exposure.

A more hopeful example comes from Karolina Jasko, who later became Miss Illinois 2018. As NBC reported, she barely noticed a thin dark streak on her thumbnail. When an unrelated nail infection sent her to the doctor, he was far more interested in the streak than in the infection. A biopsy confirmed early melanoma, and because it was caught in time, she was treated successfully. Her doctors told her that the infection may well have saved her life.

Know Your Nails, Know Your Body

Knowing your nails means knowing your body and your health. The problem is that most of us still are not aware enough to understand what certain changes might mean. In recent years, thanks in part to the media, awareness of skin cancer has grown considerably, but most of the attention goes to moles and spots on sun-exposed skin. Far fewer people know that, in rare cases, melanoma can also show up under a nail, and that a new brown streak there is something worth having a dermatologist look at.

Doctors at the Cleveland Clinic point out that nail changes can reflect anything from a simple nutrient shortfall or an injury to, much less commonly, something more serious such as nail melanoma. In other words, your nails are a useful window into your health, but they are never the whole picture.

How Common Is Melanoma Under the Nail?

Subungual melanoma is rare. It accounts for only a small share of all melanomas, roughly 1 to 3% in fair-skinned populations, but a considerably larger share in people with darker skin, according to the Skin Cancer Foundation. The tumor does not actually grow in the nail itself but in the nail matrix underneath, the tissue at the base of the nail that produces the nail plate. That is why a pigmented line forms and grows outward with the nail. Often it starts as a very faint, light streak that gradually becomes darker and wider over time.

According to the American Academy of Dermatology (AAD), nail melanoma is more common in older adults and in people with skin of color, and a personal or family history of melanoma may increase the risk. The AAD also notes that it is often diagnosed at a later stage than melanoma elsewhere on the skin, simply because people do not think to check their nails.

Warning Signs Worth a Closer Look

Dermatologists often use the "ABCDEF" rule for nail pigmentation, first described in a paper by Levit and colleagues in the Journal of the American Academy of Dermatology. In simplified form, a streak deserves a professional opinion if:

• A – Age: it appears in adulthood, especially after 50.


• B – Band: the stripe is brown or black, wider than about 3 mm, or has blurred, uneven edges.


• C – Change: it is getting wider or darker, or the nail itself is changing shape, cracking or splitting.


• D – Digit: it affects a single nail, most often the thumb, the index finger or the big toe.


• E – Extension: the pigment spreads onto the cuticle or the skin around the nail (known as Hutchinson's sign).


• F – Family history: you or a close relative have had melanoma before.

One simple clue helps tell a bruise apart from a pigmented streak. Blood under the nail after an injury (a subungual hematoma) usually moves toward the tip as the nail grows and gradually disappears. Fingernails grow only about 3 mm a month, so it takes patience, but a stripe that stays in place, starts right at the base of the nail and keeps getting wider is a reason to see a doctor.

If you notice something like this under your nails, we recommend booking an appointment with your doctor or, better still, a dermatologist. A blood test cannot confirm or rule out nail melanoma. The specialist will usually examine the nail with a dermatoscope (a magnifying device with special lighting) and, if necessary, take a small tissue sample. In most cases, the result is reassuring.

Not Every Line Is a Cause for Alarm

Keep in mind that not every line under a nail is a sign of cancer. Far from it. The quality and appearance of nails are also influenced by a lack of vitamins and minerals, nails can sometimes reflect problems with the functioning of internal organs, and the most common causes by far are simple mechanical injuries. Other frequent, harmless explanations include:

• Natural pigmentation: many people with darker skin have one or more brown streaks on several nails, which is usually completely normal.


• Injuries and pressure: tight shoes, running, a slammed door or a dropped object can leave a dark mark.


• Fungal and bacterial infections: these usually also make the nail thicker, crumbly or discolored, as described by Atlantic Health.


• Some medications: certain drugs can cause temporary nail pigmentation.


• Benign moles in the nail matrix: just like moles on the skin, these are usually harmless but are worth monitoring.

What Your Plate Has to Do With Your Nails

As nutritionists like to say, nails are a slow-motion record of what we eat. Because a nail takes months to grow out, it often reflects your diet from several months ago. According to Scripps Health, thin, soft or brittle nails may be associated with low levels of B vitamins, calcium or iron, as well as with frequent contact with detergents and nail polish remover.

Interestingly, a lack of vitamin B12 is one of the less known causes of darker nail pigmentation, and it typically affects several nails at once. You can read more about the early signals of this deficiency in our article Warning Signs of Vitamin B12 Deficiency. Iron is another key nutrient: low iron levels are linked to pale, thin and even spoon-shaped nails. If you want to make the most of the iron in your meals, take a look at 11 foods that help or hinder iron absorption.

A varied diet that includes good sources of protein, iron (legumes, meat, leafy greens), vitamin B12 (fish, eggs, dairy), zinc (pumpkin seeds, nuts) and vitamin C (fruit and vegetables) supports strong, healthy nails. Just remember that no food or supplement can prevent or treat melanoma, and a suspicious streak always belongs in the hands of a doctor.

A Simple Habit Worth Adopting

Once a month, for example when you trim your nails, take a minute to look at all twenty of them in good light, without nail polish. Many readers tell us they take a quick photo with their phone so they can compare it later and see whether anything has changed. One reader shared that she only noticed a faint line on her thumbnail after removing a gel manicure she had worn for months. It turned out to be a harmless mole in the nail matrix, but she says she would not have slept well without having it checked.

Most dark lines under the nails are harmless. But if a streak is new, changing, affects only one nail or spreads onto the surrounding skin, it is worth a short visit to a dermatologist. As Bob Marley's story reminds us, a few minutes of attention can make a big difference.