What Exactly Is 'COVID Arm'? COVID-19 Vaccines Leave Some Patients With Itchy (But Harmless) Rash

Doctors say it shouldn't deter you from getting your shot.

As with most vaccines, the COVID-19 injection comes with a few less-than-desirable side effects, like pain or swelling at the injection site, fatigue, chills, body aches, or headaches. Another reported side effect, specifically for Moderna's and Pfizer's COVID-19 vaccines: a large, red lesion around the injection site. But doctors want to reassure people that it's harmless—and it shouldn't discourage anybody from getting vaccinated.

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The side effect has been dubbed "COVID arm," but it also has a more medically-accurate label: delayed cutaneous hypersensitivity, which essentially means a delayed reaction on the skin.

"It seems to be an allergic reaction—a skin reaction that occurs after getting an injection," board-certified dermatologist Debra Jaliman, MD, who has a private practice in Manhattan, NYC, told Health.com. "We see firmness and redness at the site where the injection occurred." Some people who've experienced COVID arm also report itching and say the lesion is painful to touch.

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Mass General Hospital

What makes this side effect a little unusual is that it doesn't appear right away. "Typically, it shows up five to nine days after the first shot," Dr. Jaliman said. That makes it different from most vaccine side effects, which usually occur within a day or two.

Chris Gilbert, MD, PhD, experienced COVID arm after she had her first dose of the vaccine. "I thought I was done with the side effects when, on day seven after the vaccine shot, as I was going to bed, I started itching at the injection site," she wrote on Psychology Today. Gilbert didn't think much of it at the time and fell asleep, but when she woke on day eight, her right upper arm was very itchy. "A red, round lesion about two inches in diameter was at the place where I had the shot," she wrote.

The good news: COVID arm is a brief, harmless response. Experts are still trying to figure out exactly what's going on, but it's likely that it's simply part of the body's immune system response to the vaccine. "We want to reassure people that this is a known phenomenon," Esther Freeman, MD, director of global health dermatology at Massachusetts General Hospital told USA Today. "Having a big red splotch on your arm for a couple of days may not be fun but the reality is there's no need to panic and no reason not to get your second shot." According to Dr. Jaliman "[the rash] should go away within 24 hours to a week."

The COVID arm reaction has reportedly shown up more in women, though the association there is unclear as well. "We do have more cases that are being reported in women, but that could be that women are more likely to tell you," Kimberly Blumenthal, MD, an allergist and epidemiologist, and professor of medicine at Harvard Medical School, told USA Today.

Overall, the delayed reaction shouldn't prevent people from getting additional shots, Dr. Jaliman said, but she recommends getting it in the other arm.

To help ease the itching, she suggests an antihistamine like Benadryl, or a topical steroid. Ice would help reduce the swelling too, she said. Remember, it's not an infection and doesn't need antibiotics. But if the symptoms last any more than a week, or you experience swelling or pain anywhere else in your body, make an appointment with your doctor just to be on the safe side.

In the event you do go see your doctor for potential "COVID arm", make sure you tell them that you recently had your shot to help with the accuracy of your diagnosis. One study in the Journal of Primary Care & Community Health found that some cases of COVID arm had been misdiagnosed as cellulitis, a serious bacterial infection that requires medical attention.

If you experience any side effects at all after your vaccine, you're also encouraged to report them to either of the CDC's vaccine safety and tracking systems: the Vaccine Adverse Event Reporting System (VAERS) or V-safe.

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