Up until a few months ago, most people in the U.S. had never heard of monkeypox, let alone how to identify it. But, as case counts continue to rise, knowing how the illness can present on the skin can help point you to a diagnosis—or quell unnecessary fears.
According to the most recent data, there have been more than 9,000 confirmed cases of monkeypox in the U.S.; worldwide, the numbers top 31,000 cases across 89 countries—most of which have not historically reported monkeypox cases.
And the influx of cases has many people worrying about any lump or bump that appears on their skin. “You loved playing ‘Allergies or COVID?’ Now get ready for ‘Mosquito Bite or Monkeypox!'” read one viral tweet.
To help clear up some uncertainty about the illness, health agencies—including the U.S. Centers for Disease Control and Prevention (CDC) and the U.K.'s National Health Service (NHS)—have shared pictures to distinguish monkeypox lesions at any stage of the disease. Here's what to know.
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What Do Monkeypox Lesions Look Like?
The monkeypox virus is a type of orthopoxvirus. Although monkeypox is related to smallpox—caused by the variola virus—it’s much milder and monkeypox is rarely fatal. Neither monkeypox or smallpox is related to chickenpox, which is caused by the varicella-zoster virus.
Diseases caused by poxviruses usually cause lesions, skin nodules, or rashes to form on the skin.
In monkeypox specifically, the lesions can morph or change throughout the course of a person’s infection. While flu-like symptoms typically hit first, a person will go on to develop sores that go through five distinct stages, according to Thomas Russo, MD professor and chief of the division of infectious diseases at the University of Buffalo.
Discolored portions of the skin that are flat—called macules—are often the first stage of a monkeypox lesion. Before this stage, sometimes an enanthema, or a rash on the tongue or in the mouth, can form. These macules can last up to two days.
Next, the macules will begin to raise and turn into papules. This stage can also last up to two days.
One the lesions have turned into papules, they’ll fill with a clear fluid. This signifies the vesicular stage of the monkeypox lesions. It’s at this stage where the lesions resemble blisters. Lesions can stay in the vesicular stage for up to two days.
Once the clear fluid inside the vesicles turns opaque, the lesions have reached the pustular stage. “The fluid in the blisters gets cloudy,” Dr. Russo told Health. The pustules are typically round and hard to the touch.
At some point, those pustules will go through umblication, in which "they have a depressed dome on top of them," said Dr. Russo. This stage can last for five to seven days before the lesions begin to crust over.
“Eventually, if unperturbed, these lesions [will] eventually scab over,” said Dr. Russo. “The scabs will eventually fall off.” Scabs can stick around for about a week or up to 14 days before they completely resolve—though some pitting or skin discoloration may stick around.
Once the scab finally falls off, the person is no longer considered contagious, according to Dr. Russo.
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Where Do Monkeypox Lesions Typically Occur on the Body?
In addition to showing up in non-endemic countries, the ways in which monkeypox is presenting on the body is also different from what researchers have historically known about the disease.
“The rash that we used to see was basically erupting all at one time, so a person would tend to have lesions that were all at the same stage of disease, in the traditional sense,” Kelly Gebo, MD, MPH professor of medicine at Johns Hopkins University told Health. “Currently, we’re seeing people presenting with lesions at various different stages.”
The lesions in this outbreak are showing up in places on the body that are unusual, as well.
"The traditional spots that we saw this—on the face, and then often on the palms and soles—are different," Dr. Gebo said. "Now we're seeing people who have them in their genital region, including their mucous membranes, like their rectum, or their mouth."
The final wild card when it comes to monkeypox lesions in this outbreak is the number of sores that people seem to develop. We're seeing cases where people just have one or a few lesions, instead of dozens or hundreds, Dr. Russo explained.
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Differentiating Between Monkeypox and Other Sores or Bumps
All of this variability—both with how the sores look over the course of the infection and new symptom developments in this outbreak—may make it a bit challenging to correctly identify monkeypox.
Lesions are usually between two and five millimeters, Dr. Gebo said, around the same size as a typical pimple or bug bite. This may partially explain why people online are having trouble differentiating between a rogue pimple and a monkeypox lesion in its papule stage.
There's also a risk that monkeypox may be misidentified as a different type of sexually transmitted infection, like herpes or syphilis, that may cause similar-looking sores in genital or oral areas.
"If it's an area like the mouth or if there's friction in an area, those blisters could break down so they could look like ulcers," Dr. Russo said.
And, though it's not very prevalent in the U.S. anymore due to childhood vaccination, monkeypox could be misidentified as another kind of pox-producing illness, like chickenpox, Dr. Gebo added.
Because it can be mistaken for so many other types of other diseases and issues, there are a few helpful questions to ask yourself when determining whether that strange bump is nothing, or the beginning of a monkeypox infection.
"Are you feeling sick? And so do you have a fever? Do you have chills? Do you have night sweats or swelling of the lymph nodes? That would make me think more of a systemic illness as opposed to a bug bite or a pimple, which is generally a very localized skin reaction," Dr. Gebo said.
The other important thing to keep in mind, Dr. Gebo explained, is whether or not you think you may have been in a situation where you could have been exposed to monkeypox.
Because the disease is primarily spreading among men who have sex with men, if you’re in that community it’s best to err on the side of caution if you believe you may have monkeypox. The same is true, though, for anyone who has had close skin-to-skin contact with other people, whether it’s sexual or not.
However, the only way to be completely confident that what you're looking at is a pimple, monkeypox lesion, or something else entirely, is to get a test. "Always when in doubt, using objective diagnostic testing is helpful," said Dr. Russo.
If you suspect you have monkeypox, talk to your healthcare provider about getting tested—they will be able to initiate the process of a diagnosis, which can only be confirmed at some specific laboratories, nationwide. However, you will likely only be able to get tested for monkeypox if you don’t yet have lesions—swabbing a lesion is the only way to test for the illness.
Although testing capacity is limited, Dr. Russo hopes that it will soon expand. "I think the approach we need at this point is to have a low diagnostic threshold," he said. "Where, if anyone has [any] sort of ulcerative lesions in these areas, [they should get tested]."