Your Random Rash Could Be Pityriasis Rosea

At first, I thought it was a mosquito bite. It looked like one, and it certainly itched like one — but then more came. What started as a single, quarter-inch raised welt on my left rib cage eventually morphed into two, then four. I put on some hydrocortisone and went to sleep, then woke up with another mark on my side, a couple inches below my armpit. I figured a very determined mosquito had snuck into my room and attacked me through my tank top. A few days later, the cluster came: Ten little dots arranged themselves in a perfect alien-like crop circle on my upper back, and they itched so much that I scratched them raw. I video-chatted with my dermatologist who asked a few questions: Did I have body aches or flu-like symptoms? (No.) Had I started new medication? (No.) How quickly did it come on, and did my boyfriend also have it? (Within two days, and still no.) She diagnosed it as pityriasis rosea, a benign but frustratingly itchy rash that — in her words — just happens sometimes.

What is pityriasis rosea?

Pityriasis rosea is a benign inflammatory rash that starts with a single red rash, also known as the "herald patch," which eventually gives way to a larger, similar-looking rash on the trunk within days or weeks, says dermatologist Corey L. Hartman, founder of Skin Wellness Dermatology in Birmingham, Alabama. Luckily, it's not contagious.

While it can spread all over the entire body, PR usually favors the trunk, says dermatologist Christina Lam, an assistant professor of dermatology at Boston University School of Medicine. "Sometimes it can spread to what we called the proximal extremities, meaning the parts that are closer to the trunk, so the shoulders, upper arms, [and] the thighs," she says. "It's usually not from head to toe — that's more atypical — but there are some people that get it more in the groin area or in the armpit rather than on the trunk predominantly, which is just a variant."

Those ensuing spots — like the circle of dots that erupted on my back a day after the initial raised welt appeared — typically resemble a Christmas tree-like formation. It's also what's known as a self-limiting rash, Hartman says, in that it can resolve itself on its own without treatment in about six to eight weeks. Some rare cases can take up to three months. PR also tends to occur in patients between the ages of 10 to 35 that are usually otherwise healthy, Lam says.

The good news is many of those who develop pityriasis rosea never get it again, says New York City-based dermatologist Hadley King. "However, it's possible to develop the rash more than once," she says. "In studies, between 2 and 3 percent of people develop the disease again. While unusual, one patient developed pityriasis rosea once a year for five years in a row."

What causes pityriasis rosea? 

Though there's no single-known cause, King says, "pityriasis rosea is associated with reactivation of herpesviruses 6 and 7 [HHV-6 and HHV-7, respectively], which cause the primary rash, roseola, in infants. Influenza viruses and vaccines have triggered pityriasis rosea in some cases."

As King notes, there have been some reported cases of pityriasis rosea occurring in patients after receiving certain vaccines, like the flu shot. The authors of one 2014 case report of a 71-year-old man who suffered from pityriasis rosea one month after receiving an influenza vaccine concluded that "altered immunity" could result in reactivation of HHV-6 and/or HHV-7 which may have triggered an atypical presentation of PR. A more recent letter in the International Journal of Dermatology reported a "unique case of pityriasis rosea following administration of mRNA COVID-19 vaccine." The authors suggest more research is necessary.

"There's some emerging data … where there are certain skin rashes that seem to be more associated with the COVID vaccine, and pityriasis rosea is one them. Flares of other types of skin conditions [like psoriasis] sometimes have been described as well," says Lam. "Like a lot of things in dermatology, unfortunately, we're not always sure what causes these rashes," says Lam. "Any type of stress on the body can sometimes [cause them, and] any vaccine, not just the COVID one."

While annoyingly itchy, the rash does not cause any serious long-term side effects and is not contagious, unlike the diseases these vaccines protect against.

What are the symptoms of pityriasis rosea?

The herald patch is the telltale sign that your rash could be PR, but there are other common (though not universal) symptoms as well. While my particular flare-up itched a lot, that's not always the case. Similar to other viral outbreaks, people can experience flu-like symptoms like a fever, aches, or a runny nose when the herald patch shows up, Lam says, though I was lucky enough to skip that step.

The rash itself usually doesn’t blister or bleed, but in many cases, the skin may peel. And the itch usually only lasts for a few days — mine finally let up around day seven — but the rash can leave behind dark marks that eventually resolve on their own, Lam says. (Unfortunately, I scratched my rash until it bled, so my hyperpigmentation may linger.)

How is pityriasis rosea diagnosed?

At first, I thought it could be a fungal infection like ringworm, a common misdiagnosis, says Hartman, but my dermatologist ruled that out when I mentioned the additional spots erupting on my back via our video chat.

Shingles was another fear, as I had chicken pox when I was four, but we ruled that out too: "Shingles is a nerve-mediated process; it tends to be very painful, not so itchy," Lam says. "And it has a particular [dermatomal] distribution because it's along a nerve," which also presents as fluid-filled blisters, rather than lesions. "It looks very different."

According to King, an in-person skin exam is usually enough to make an accurate diagnosis, though a biopsy or blood work may be necessary for some. Though there's no single-known cause, it may be brought on by a drug interaction, or the reactivation of herpes simplex virus 6 or 7.

Lastly, Hartman says PR can present differently in patients with darker skin: "The characteristic erythematous plaques may appear more hyperpigmented or violaceous in darker skin types. In my experience, patients with darker skin are more likely to present with atypical forms of the disorder. For instance, the rash sometimes appears only under the arms or on the flanks. The typical distribution of the rash is on the trunk between the neck and the knees."

How is pityriasis rosea treated?

Pityriasis rosea usually resolves on its own without treatment in most cases, King says, but topical corticosteroids can be used for itchy control if necessary, which is what I used. "Other treatments including phototherapy or oral medications can be considered for extensive or persistent cases, [and] some small case studies support the use of oral antivirals like acyclovir or oral anti-inflammatory antibiotics erythromycin," King explains.

In addition to a corticosteroid cream, New York City-based dermatologist Macrene Alexiades recommends keeping showers short and lukewarm, as "water, sweat, and soap reportedly irritate and inflame the lesions. I tell my patient to use a gentle non-soap cleanser." I also had to stop working out and hiking for about a week, as Alexiades is right — excessive perspiration worsened the itch.

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