It started as a mini constellation of red dots near the right corner of my lips. Probably just “maskne,” I figured. I slathered on some acne cream and tried to forget about it.

But the inflamed, rashy spots didn’t fade away. In fact, they grew larger, spawning dandruff-like scales and flakes. Within days, the red dots had spread to the left side of my mouth, and even — to my horror — sprinkled across my eyelids. When I opened my mouth, I felt the raw, burning skin at the corners crack.

After a telemedicine visit with my dermatologist, I learned that I had perioral dermatitis — a noncontagious facial rash that often shows up as clusters of tiny, scaly, red, uncomfortable bumps above irritated skin. “We see it mainly around the mouth,” said Dr. Anna Chien, a dermatologist at the Johns Hopkins University School of Medicine. “Some people can have similar breakouts around the eyes.”

Cases have become more common since the coronavirus outbreak began, some experts say. In one Canadian survey of 77 dermatologists published in September, more than a third reported either a large or slight increase in perioral dermatitis instances since the beginning of the pandemic.

“In our clinic,” Dr. Chien said, “we are seeing many more perioral dermatitis and other rashes related to masks.” Dr. Jessica Sprague, a dermatologist at the U.C. San Diego School of Medicine, noted a similar phenomenon. “Masks alter the skin environment, and they can also cause a lot of skin irritation,” she said, adding, “I’m definitely seeing it more now in the setting of mask wearing.”

What causes it

Perioral dermatitis might look a lot like acne, but the resemblance is deceptive, said Dr. Carrie Kovarik, a dermatologist at the Hospital of the University of Pennsylvania and a member of the American Academy of Dermatology’s Covid-19 task force. “People confuse it with ‘maskne,’ and they are two different things.”

With mask-induced acne, your pores get clogged with dirt, skin flakes or oil, giving rise to inflamed cysts that may burst. But perioral dermatitis is more of an inflammatory rash. There can be various causes, but it tends to be triggered by a disruption of your skin’s natural equilibrium, Dr. Sprague said, from the use of topical substances like steroid medications or irritating cosmetics.

The humid, enclosed space behind a mask may also encourage perioral dermatitis rashes to form. “Depending on what kind of mask you’re wearing, you could really have a lot of moisture sitting there on your face,” Dr. Kovarik said. “You’re almost creating this skin fold-type area,” a little like the damp crevices that can form between rolls of skin.

That can modify the face’s natural microbial balance, research suggests, contributing to perioral dermatitis and related conditions. “When you wear a mask, you’re basically changing the terrain,” said Dr. Whitney Bowe, a dermatologist based in New York.

This can encourage or discourage the growth of certain microbes, like bacteria and yeast, which may be involved in perioral dermatitis, and can touch off “this cycle of making the disease even worse,” Dr. Kovarik said.

The rash appears most often in adult women, but can also crop up, albeit less frequently, in young children. Unlike cold sores, perioral dermatitis bumps are not thought to be caused by a specific virus and usually do not migrate onto the lips themselves.

How to prevent and treat it

Since perioral dermatitis is so complex, it can be challenging to treat and may take a long time to clear, Dr. Sprague said. But if you monitor your skin closely and follow some simple rules, you might be able to steer clear of the condition completely or nip it in the bud.

Practice good mask hygiene. Masks are currently a public health necessity, but cleaning them regularly may help keep perioral dermatitis at bay.

As soon as you are home and can safely remove your mask, wash your face with a gentle, fragrance-free cleanser, Dr. Sprague said. When it’s time to don your mask again, resist the temptation to use one that is dirty, since it can disrupt your face’s microbial balance. “It’s like underwear,” Dr. Bowe said. “You wouldn’t wear your underwear two days in a row.”

Avoid steroid-based skin creams. Many people use steroidal anti-inflammatory medications, like hydrocortisone cream, to manage symptoms of perioral dermatitis, Dr. Chien said, but while such medications may clear redness temporarily, a rebound rash is likely to appear once you stop using them. “It’s very reasonable to think, put on some steroids, but that tends to make it worse,” she said. “The minute you stop, it comes back with a vengeance.”

Researchers don’t completely understand why this happens, but some think that steroid creams might allow bacteria to overgrow by suppressing the body’s local immune response.

If you have allergies or asthma, think about switching your meds. As with steroid creams, Dr. Sprague said, inhaled or spray steroidal medications commonly used to treat allergies or asthma — like Flonase, Nasacort or Symbicort — are thought to trigger perioral dermatitis, perhaps because they modify the body’s immune response.

If you use any of these medications and are worried about perioral dermatitis, talk with your doctor about your treatment plan. Some allergy or asthma sufferers may need to remain on steroid medications, Dr. Sprague said. However, others may be able to consider other nonsteroidal drugs, like cetirizine (Zyrtec), which are not thought to cause perioral dermatitis.

Streamline your skin-care products. Using too many skin care products can throw off your skin’s natural balance, according to Dr. Bowe, increasing the risk of an outbreak. In one study of 232 people in Australia, those who used foundation, night cream and moisturizer were 13 times more likely to develop perioral dermatitis than those who used moisturizer alone.

Similarly, if you’re managing a flare, minimalism is key. “The best thing you can do is baby your skin,” Dr. Sprague said. “Stop any thick cosmetics, serums, etc.”

Dr. Jennifer Holman, a dermatologist in Tyler, Texas, recommended washing your face twice a day with a gentle cleanser, such as a sulfur face wash, and following up with a fragrance-free moisturizing lotion. It’s OK to use a little mineral makeup, she added, because it doesn’t tend to aggravate the rash.

Don’t dabble in unproven treatments — see your dermatologist. Plenty of alternative treatments for perioral dermatitis are available on the web, from swabbing the skin with apple cider vinegar to taking supplements of certain herbs, like neem. But those haven’t been scientifically proven to work, Dr. Holman said. And since the rash is notorious for sticking around, it’s important to seek professional help.

Dr. Sprague said she’ll often start by prescribing a topical antibiotic, like metronidazole — not to banish an infection per se, but to reduce the inflammation and give the skin a chance to heal. Pimecrolimus, a nonsteroidal anti-inflammatory cream that is commonly used to treat rosacea and eczema, can also help clear up the rash.

When these treatments fall short, Dr. Sprague said she’ll sometimes recommend a several-week course of an oral antibiotic, like doxycycline, which can also help to reduce inflammation.

Perioral dermatitis “seems like something minor, but you can really get into difficult situations” where the rash persists, Dr. Kovarik said. “You want someone who’s familiar with treating this.”

My own perioral dermatitis has improved since I started treating it with a topical antibiotic and a gentle, fragrance-free lotion, but it hasn’t yet vanished. I still have some tiny bumps around my mouth and eyes, so I’m leveling up with a monthlong course of oral doxycycline. I hope it will restore my clear skin — and I look forward to a post-pandemic future when I can let my face breathe freely once again.

Elizabeth Svoboda is a science writer in San Jose, Calif., and the author of “What Makes a Hero?: The Surprising Science of Selflessness.”