Are 'covid nails' a sign you had the virus? Experts weigh in.

An example of “covid nails” that has been observed by Tim Spector, principal investigator for the Zoe COVID Symptom Study. (Zoe COVID Study)
·5 min read

At this point in the pandemic, the coronavirus's devastating effects on the human body have been well documented. But unusual symptoms that may be connected to the virus continue to crop up, including "covid toes," "covid tongue" and hair loss.

Now, news reports and social media posts have documented visible changes in the nails of some covid-19 survivors, most commonly in the form of horizontal grooves. Dubbed "covid nails" by a U.K.-based epidemiologist who tweeted about the markings earlier this month, the anecdotal reports have prompted assertions that it could be a way to tell whether you've had the virus.

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Other experts, however, caution against relying on your nails as proof that you may have been infected. "Whether it comes to nail changes or skin rashes or hair loss, these are not necessarily things that covid does because it's covid," said Jeffrey Weinberg, an associate clinical professor of dermatology at Mount Sinai in New York. Those symptoms, Weinberg said, "could happen with anything that perturbs the body."

Here's what Weinberg and other experts had to say about nail changes observed in coronavirus cases.

Q: Can illnesses such as covid-19 affect your nails?

A: "A lot of different illnesses and infections can cause nail changes," said Esther Freeman, director of global health dermatology at Massachusetts General Hospital and principal investigator for an international registry of dermatologic reactions related to the coronavirus. But Freeman noted, a "relatively small proportion" of health-care providers has been reporting unusual-looking nails to the registry.

Of the nail symptoms detailed in the registry, the most commonly reported phenomenon is Beau's lines, or the horizontal grooves that have been associated with "covid nails," said Freeman, who suggested a more precise name would be "post-covid nails." The grooves often appear across all fingernails and occasionally on toenails.

Beau's lines result from "a temporary interruption in the nail growth," she said. "If you run your fingers over it, it's going to just feel like a change in texture."

Q: How do Beau's lines form?

A: Scientists don't know exactly what causes nails to briefly stop growing, said Shari Lipner, a nail expert and dermatologist at Weill Cornell Medicine in New York. It's believed to be a response to the body weathering "any shock to the system," including systemic illnesses that are accompanied by high fever or a medical event such as chemotherapy or surgery, Lipner said. Beau's lines, for instance, have been seen in people who had the flu or hand, foot and mouth disease. Studies have also reported the appearance of the lines in some deep-sea divers and people who spent time at high altitudes.

"Not everybody is going to get them," Weinberg said. "Why will one person get it and another will not, I have no idea."

Because the interruption happens in the area where your fingernails and toenails start to grow, which is called the nail matrix, the lines aren't visible right away, Lipner said. If you notice a groove near the base of your nail close to the cuticle, the triggering event likely happened at least a month before.

"It's really not something to be concerned about," she added. "It's really just saying that something happened to your body beforehand."

Though covid could be causing Beau's lines, Lipner emphasized that reported cases have been infrequent. "If it does happen with covid-19, it's a rare occurrence."

Tim Spector, the epidemiologist who tweeted about "covid nails" earlier this month, is the principal investigator for the Zoe covid Symptom Study app and said he estimates reports of nail changes documented by the app's users are "in the hundreds" at the moment - a number he anticipates might rise as awareness increases. The app, which is available to people in the United States, the United Kingdom and Sweden and has racked up about 4.5 million downloads, is designed to study covid-19 symptoms and track the virus's spread, Spector said.

"We are increasingly finding out that people do respond to the virus in different ways," said Spector, a professor of genetic epidemiology at King's College in London. "This just might be yet another of these rather odd clinical signs discovered weeks or months afterward."

Q: Are Beau's lines a reliable sign that you had covid?

A: No, the dermatologists said.

"This is a very nonspecific finding, and people can get Beau's lines from many, many different conditions," Freeman said. "I would certainly not view it as a way to diagnose acute covid infection, because you won't see it in the acute period." And you shouldn't use the lines in place of an antibody test, she added.

For covid to be the likely cause of Beau's lines, Lipner said, symptoms and timing would need to line up. If you had a confirmed infection and the lines appeared about a month later, then it's possible they were related to covid, she said.

Freeman said she has seen reports in the dermatology registry detailing nail abnormalities other than Beau's lines in coronavirus patients. Some people have observed the red or purple skin discoloration, also known as pernio or chilblains, that can appear under the toe nails and has been called "covid toes." Additionally, there have been splinter hemorrhages, which show up as small red or purple spots and are linked to tiny blood clots in the capillaries underneath the nails, and cases of brittle nails splitting and peeling at the ends. All of these changes, like Beau's lines, also can have other causes and aren't specific symptoms of covid, Freeman said.

Another finding that has been documented in at least two dermatology journals during the pandemic is what researchers are calling the "red half-moon nail sign," which appears as reddish bands that surround the white base of the fingernail. It's not yet known what's causing this symptom, but the authors of one paper theorized that it could be a secondary result of vascular inflammation.

Q: Are these nail changes permanent?

A: Most nail changes, including Beau's lines, aren't permanent, experts said, and shouldn't be cause for panic.

On average, fingernails completely grow out over a six-month period, while toenails can take 12 to 18 months. The appearance of a single set of Beau's lines, Freeman said, simply shows "that your body went through something, and it's on the road to recovery."

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