15 Signs You May Have Already Had Covid-19, Doctors Reveal

By now, we've all known someone who's had Covid-19. Were you infected without realizing it? Here's what the experts say you should look for if you think you've been infected.

Recently, you felt exhausted and had a major stuffy nose and headache. Could it have been Covid-19?

Most of us are aware of the history: the Covid-19 pandemic began in Wuhan, Hubei Province, China in December 2019. Fast-forward almost three years, and in the second half of 2022, according to Johns Hopkins University there have now been almost 600 million documented Covid-19 cases around the globe. This includes over 93 million confirmed cases in the U.S., and counting. More than one million people have died from Covid-19.

If you haven’t been diagnosed with Covid-19 by now, it might feel like you’re one of the lucky few. Or maybe, just maybe, you already had Covid and didn’t realize it because your symptoms were so mild. (This might have made any Covid-19 booster side effects worth it!)

If you have felt a little “off” in recent months but didn’t know quite what was going on, here are 14 silent signs that you may have been infected with Covid-19—and what that means for you now.

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woman wearing face maskkasto80/Getty Images

Covid-19 sign: You’ve got natural antibodies

Matthew B. Laurens, MD, MPH, a professor of pediatrics at the University of Maryland School of Medicine in Baltimore, says no one is recommending routine antibody testing to see if you have had COVID-19 or have mounted a response to the COVID-19 vaccines at this time. However, these tests are available. “There is an antibody test that can tell you if you have been exposed to natural infection, and there is a different antibody test that looks at response to the COVID-19 vaccine,” Laurens explains.

Specifically, antibodies to nucleocapsid protein only appear if you have recovered from Covid-19, while vaccines and natural infection produce an antibody to spike proteins. “If you are positive for antibodies to the spike protein and negative for antibodies to nucleocapsid protein, you have been vaccinated, but not exposed,” he says—adding: “If you are positive for both, you have had COVID-19 and you may or may not have been vaccinated.”

There is still a lot research is discovering about antibodies, including how long they last and what level is considered most protective…or, for how long.

Covid-19 sign: You were feeling run down a few months back 

Fatigue is a common symptom—and lingering effect—of Covid-19. But for those of us with busy lives (that’s just about everyone!), sometimes it’s simply hard to tell typical tiredness from something more serious. “If you didn’t feel sick enough to consider getting tested, you could have had Covid-19 and recovered without an official diagnosis.”

Screenshot our infographic for handy reference anytime.

Spotting Covid-19 infographic that breaks down the symptoms of covid-19, delta variant, omicron variant, and fluGrace Luxton/The Healthy, Getty Images

Covid-19 sign: Brain fog

Changes related to the brain—undiagnosed or uncharacteristic depression, confusion or trouble focusing, as examples—are pervasive Covid-19 symptoms that haven’t gotten a great deal of attention. Read What Is Covid-19 Brain Fog—and How Do You Get Rid of It?

Covid-19 sign: Your fever and cough weren’t the flu

You had a fever for days, a hacking cough, and were exhausted, but your flu test was negative. It could have been Covid-19, says Adam Spivak, MD, an infectious disease doctor at the University of Utah in Salt Lake City, noting that flu season and the Covid-19 pandemic overlapped.

In the past year, doctors have seen cases of flurona. “If you weren’t tested at the time or you were negative for other tests such as the flu, it could have been Covid-19,” Spivak says. “There is so much overlap with colds or flu and coronavirus symptoms, which is why testing for Covid-19 has been so emphasized.” (We’ve broken down the flu vs. coronavirus symptoms here.)

Covid-19 sign: You suddenly lost your sense of smell or taste

You’ve heard this: loss of sense of smell or taste is a hallmark of Covid-19 infection with earlier variants. What you may not know is that these symptoms are not a slam dunk by any stretch, says Benjamin Singer, MD, an assistant professor in pulmonary and critical care at Northwestern University Feinberg School of Medicine in Chicago.

Covid-19 sign: Your hair is falling out in clumps

If you’re noticing hair loss, it could be due to a past infection with Covid-19, says Alexis Young, MD, a dermatologist at Hackensack University Medical Center in New Jersey. “This phenomenon is known as telogen effluvium and occurs when physical or psychological stress causes hair roots to be pushed into a resting state prematurely,” she explains. “It’s not specific to Covid-19, but I am seeing lots more of it among people who are recovering from Covid-19, including some who may not have known they were infected in the first place.”

The good news is that your hair will likely come back. “Hair follicles aren’t permanently damaged with telogen effluvium,” this dermatologist says. “Shedding can continue up to six months, and full recovery can take up to 18 months because hair grows back so slowly.”

Covid-19 sign: You’ve got hives 

Post-Covid-19 hives are a phenomenon health professional have observed, Young says. “We are also seeing viral exanthems, which is a skin rash that is often related to a viral infection after Covid-19,” she says.

These seem to be more common in children than adults and can even occur if you didn’t have any noticeable Covid-19 symptoms. These hives and rashes usually resolve on their own with judicious use of moisturizer or topical steroids, if the itch is particularly bothersome.

Covid-19 sign: Your loved ones were infected

If Covid-19 passed through your house taking no prisoners except you, it’s possible you were infected and didn’t realize it. Many people who are infected with this virus have mild or no symptoms, and Omicron reportedly produces even milder symptoms than other variants—especially among people who are vaccinated or boosted, says Dr. Len Horovitz.

Covid-19 sign: You just didn’t test at the right time

It’s possible you missed the infection even if you were tested, Horovitz says. “Any test you take is snapshot of the past 12 to 24 hours, and you can’t extrapolate from a single test,” he says. “Depending on when and how you tested, you may not have caught the infection.” At-home Covid-19 antigen tests aren’t that sensitive either, so you may have received a false negative.

Covid-19 sign: Your toes were affected

“Covid toes” can happen, Dr. Singer says. Covid toes are marked by purple or red, itchy wounds. “Skin manifestations, particularly of the toes, could be something that makes people who weren’t tested look back and say, ‘Was that a manifestation of Covid-19?'” he says.

He cautions that toes with this appearance aren’t a sure sign of Covid-19, as there could be other causes. If you have questions, talk to your doctor.

woman sick at home with headache and feverBrothers91/Getty Images

Covid-19 sign: Your stomach was acting up

Covid-19 is a respiratory illness, but not everyone coughs or gets short of breath. For some, diarrhea may be the only sign of infection, Dr. Horovitz says.

If you have digestive symptoms such as diarrhea, nausea, or vomiting and were in contact with individuals infected with Covid-19, you should have a higher index of suspicion, he says. (Also, these remedies for diarrhea may help.)

Covid-19 sign: You had a stroke out of the blue

There’s a link between Covid-19 and stroke risk, even among younger patients. Here’s what doctors and researchers know so far about stroke risk and coronavirus.

Also, here are the warning signs of stroke, and what to do if you suspect a stroke.

Covid-19 sign: You woke up with pink eye

Pink eye infection, or conjunctivitis, may be a sign of coronavirus—but this has been relatively rare, according to the American Academy of Ophthalmology. If you develop pink eye, don’t panic. “Call your ophthalmologist to let them know and follow their instructions for care,” the Academy suggests.

Covid-19 sign: You’ve got cotton mouth

Is your dry mouth a symptom of Covid-19?

Maybe. As many as 40 percent of people with Covid-19 may experience symptoms of dry mouth during or after the illness, according to a study in the Journal of Dental Research. And now research in the journal Nature Medicine provides clues as to how Covid-19 affects the mouth and saliva.

Researchers from Wellcome Sanger Institute in Cambridge, U.K. and other organizations in the U.S. and U.K. identified the angiotensin-converting enzyme 2 receptor, or ACE2 receptor, in cells of the salivary glands and tissues lining the mouth. This is the protein that SARS-CoV-2 locks into for entry into the body.

They also found that the virus can multiply in the cells of your salivary glands.

Covid-19 sign: You’re experiencing “phantom smells”

Some people recovering from Covid-19 report that they constantly smell smoke, garbage, or even skunk-like odors that aren’t really there. These phantom smells tend to become more common over time, with recent figures suggesting that about 25 percent of people experienced these otherwise unexplainable smells soon after diagnosis, according to the preprint server medRxiv. (This information has not yet been peer-reviewed.)

How to prevent Covid-19 infection

There is still a huge role for prevention, Horovitz says. “Get vaccinated and boostered when you are able to,” he says. “Wear masks when inside public spaces and places and practice social distancing.” (Here’s why you still need to wear a mask indoors if you’re vaccinated.)

Also be sure to wash your hands with soap or water before, during, and after preparing food or eating. Also wash after caring for someone at home who is sick, treating a cut or wound, going to the bathroom, changing diapers, blowing your nose, coughing, or sneezing. If a sink isn’t available, use a hand sanitizer that contains at least 60 percent alcohol.

Next, find out who is at highest risk from Covid-19.

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Denise Mann, MS
Denise Mann is a freelance health writer whose articles regularly appear in WebMD, HealthDay, and other consumer health portals. She has received numerous awards, including the Arthritis Foundation's Northeast Region Prize for Online Journalism; the Excellence in Women's Health Research Journalism Award; the Journalistic Achievement Award from the American Society for Aesthetic Plastic Surgery; National Newsmaker of the Year by the Community Anti-Drug Coalitions of America; the Gold Award for Best Service Journalism from the Magazine Association of the Southeast; a Bronze Award from The American Society of Healthcare Publication Editors (for a cover story she wrote in Plastic Surgery Practice magazine); and an honorable mention in the International Osteoporosis Foundation Journalism Awards. She was part of the writing team awarded a 2008 Sigma Delta Chi award for her part in a WebMD series on autism. Her first foray into health reporting was with the Medical Tribune News Service, where her articles appeared regularly in such newspapers as the Detroit Free Press, Chicago Sun-Times, Dallas Morning News, and Los Angeles Daily News. Mann received a graduate degree from the Medill School of Journalism at Northwestern University in Evanston, Ill., and her undergraduate degree from Lehigh University in Bethlehem, Pa. She lives in New York with her husband David; sons Teddy and Evan; and their miniature schnauzer, Perri Winkle Blu.