Jean, 71, has always prided herself on her hands. As a retired seamstress from Minnesota, she spent decades guiding fabric through a sewing machine, her fingers nimble and precise. So when she noticed thin, brown lines running up her thumbnail last winter, she brushed it off as a “quirk”—maybe a scratch from sorting through her fabric stash, or a side effect of the nail polish she’d used for holiday parties. She ignored them for months… until one morning, while buttoning her coat, she noticed the line had gotten wider. That’s when she made an appointment with her dermatologist.
What she learned stopped her in her tracks: those lines weren’t a “quirk”—they were a warning sign. “The doctor called them melanonychia,” Jean says. “She said they’re usually harmless, but sometimes they can mean something more serious—like skin cancer under the nail. I had to get a biopsy, and for two weeks, I was a wreck. Thank God it came back clear, but I’ll never ignore a line on my nail again.”
If you’re over 50, take a look at your fingernails right now. Chances are, you’ve got some lines—vertical ones, horizontal ones, maybe even a few discolored spots. We tend to write them off as part of aging: “My nails are just getting brittle,” or “It’s from all the gardening I do.” But dermatologists across the U.S. say those lines are often your body’s quiet way of sending messages—about nutrient gaps, thyroid issues, even serious illnesses. And learning to read them could save you from a lot of trouble down the road.
Let’s start with the most common ones: vertical lines. You know the ones—thin, faint lines that run from the base of your nail to the tip. If you’ve had them for years and they haven’t changed, don’t panic. “Vertical lines are usually just a sign of aging, like gray hair or wrinkles,” says Dr. Marcus Reed, a dermatologist in Seattle who specializes in senior skin health. “As we get older, the matrix—the part of the nail that grows new cells—starts to slow down. That can create tiny ridges in the nail as it grows. They’re harmless, and there’s not much you can do to get rid of them—though keeping your nails moisturized can make them look smoother.”
But here’s the catch: if those vertical lines are dark (brown or black), or if they’re new, wide, or only on one nail—pay attention. Those are the melanonychia lines Jean had. “Most of the time, dark vertical lines are caused by an increase in melanin, the pigment that gives skin its color,” Dr. Reed explains. “That can happen from things like sun exposure, hormonal changes, or even a small injury to the nail. But in rare cases—about 1% of the time—they can be a sign of subungual melanoma, a type of skin cancer that forms under the nail. It’s more common in people over 50, especially those with darker skin, and it’s often missed because people think it’s a bruise or a stain.”
Dr. Reed says the key to telling the difference is the “ABCDE rule”: Asymmetry (is one side of the line different from the other?), Border (is it blurry or irregular?), Color (is it a single color, or does it have shades of brown, black, or red?), Diameter (is it wider than 3 millimeters—about the width of a pencil lead?), and Evolution (is it getting bigger or darker over time?). “If a line checks any of those boxes, see a dermatologist right away,” he says. “Subungual melanoma is treatable if caught early, but if it spreads, it can be deadly. I had a patient last year—68, a retired golfer—who ignored a dark line on his index finger for a year. By the time he came in, the cancer had spread to his lymph nodes. It’s a tragedy that could have been avoided.”
Now, let’s talk about horizontal lines—also called Beau’s lines. These are thicker, more noticeable lines that run side to side, across the nail. Unlike vertical lines, they’re almost never just “part of aging.” “Horizontal lines are like a time capsule,” Dr. Reed says. “They form when something disrupts nail growth—usually a illness, injury, or even a period of extreme stress. The nail stops growing for a few weeks, then starts again, leaving a ridge. If you look at the line, you can even guess when the disruption happened: nails grow about 1 millimeter a week, so a line halfway up the nail means whatever caused it happened about 6-8 weeks ago.”
For seniors, common causes of Beau’s lines include high fevers (from the flu or pneumonia), thyroid problems (an underactive thyroid can slow down nail growth), or nutrient deficiencies—especially low levels of zinc or protein. “I had a patient, 65, who came in with horizontal lines on all her nails,” Dr. Reed says. “She’d been feeling tired for months, but she thought it was just ‘old age.’ We did blood work, and it turned out she had a severe zinc deficiency—from a diet that was mostly processed foods. Once she started taking supplements and eating more zinc-rich foods (like oysters, nuts, and beans), the lines stopped forming, and her energy came back.”
Then there are the lines that aren’t really lines at all—like white spots or bands. You might call them “leukonychia,” and they’re usually caused by minor injuries (like slamming your finger in a drawer) or a lack of calcium. But if you have white bands that go all the way across the nail—called Muehrcke’s lines—that’s a sign your body is low on albumin, a protein in your blood that helps carry nutrients and hormones. “Albumin levels drop when you’re not eating enough protein, or if you have liver or kidney problems,” Dr. Reed says. “I had a 73-year-old patient with Muehrcke’s lines who didn’t realize she was malnourished. She’d been living alone since her husband passed, and she wasn’t cooking proper meals—just cereal for breakfast, sandwiches for lunch. Once she started working with a nutritionist, her albumin levels went up, and the white bands faded.”
So what should you do if you spot a line (or spot) on your nail that worries you? First, take a photo. “Nail changes happen slowly, so having a photo to compare to can help you see if it’s getting bigger or darker,” Dr. Reed says. Then, keep an eye on it for a few weeks. If it doesn’t go away, or if it changes—see a dermatologist. “A lot of seniors are hesitant to make appointments for ‘small’ things, but your nails are part of your skin, and dermatologists are trained to spot problems there,” he adds. “A biopsy is quick—they numbs the area, takes a tiny sample of the nail or the skin under it—and it’s the only way to know for sure if something is serious.”
In the meantime, there are simple things you can do to keep your nails healthy—so they can keep sending you those important messages. Eat a balanced diet: load up on protein (chicken, fish, tofu), zinc (oysters, pumpkin seeds), and biotin (eggs, avocados)—all nutrients that help nails grow strong. Wear gloves when you’re gardening, washing dishes, or using harsh chemicals—this protects your nails from injuries and irritation. And avoid biting your nails or picking at your cuticles—both can damage the matrix and lead to irregular growth.
Jean, the retired seamstress, now checks her nails every Sunday night while watching her favorite TV show. She keeps a small notebook where she jots down any changes—“Thumb line: same width,” “Index nail: no new spots”—and she’s even gotten her bridge club friends to start checking their nails too. “It’s become a little ritual,” she laughs. “We’ll be sitting around playing cards, and someone will say, ‘Hey, let’s check nails!’ It sounds silly, but if it helps one of us catch something early, it’s worth it.”
The bottom line? Your fingernails are more than just a canvas for polish or a tool for opening jars. They’re a window into your health—one that’s easy to overlook. So the next time you’re washing your hands, or tying your shoes, or flipping through a magazine—take a second to look at your nails. If you see a line that makes you go, “Huh, when did that get there?”—don’t ignore it. Your body is talking. All you have to do is listen.