WASHINGTON – When one of Noëlle Sherber’s patients came to see her several months ago, dermatologist noticed that the woman had an eye infection. It was a small sty and easily treatable, but Sherber still wanted to know what caused it.

Sherber learned that the patient, who had been at home since mid-March, had recently put on a full face of makeup using products that largely had sat untouched for months after she, like many others, scaled back her usual beauty routine during the coronavirus pandemic.

“I asked, ‘How old is your mascara? Your eyeliner?’ ” said Sherber, a fellow of the American Academy of Dermatology and co-founder of Sherber and Rad. The woman, Sherber noted, had not purchased new cosmetics in a while and seemed to think that because she was not using her eye makeup often that it “extended the life span of the product.”

Even though many of us have felt as if we’ve been frozen in time since the beginning of the pandemic, Sherber and other experts emphasized that “the clock marches on” for makeup and skin-care products, which typically have shorter shelf lives than most people expect and can become contaminated with potentially harmful microbes.

“Some people think that what’s contaminating their products is daily use – opening, closing, applying to the face,” said Kathleen Suozzi, director of the Aesthetic Dermatology Program at the Yale School of Medicine. Although frequency of usage is a factor, the real “Achilles’ heel,” Suozzi said, is when preservatives in products start breaking down, leaving the makeup more susceptible to growing bacteria, such as Staphylococci or E. coli, that may cause skin irritation, or worse, infection.

In the eyes of dermatologists, most people fall short in their efforts to keep makeup products clean. “It’s challenging, because we are all moving so fast when we’re in the bathroom and we’re getting ready in the morning,” said Pooja Sodha, director of the GW Center for Laser and Cosmetic Dermatology. “It’s the smallest things that we forget to do that can potentially contaminate our makeup.”

Makeup users also tend to be overconfident that cosmetics can “stick around for a long time and be usable just because it looks normal and doesn’t have an off smell,” Sherber said. “But microscopically, there can still be a lot going on.”

A 2019 study out of the United Kingdom examined used lipsticks, lip glosses, eyeliners, mascaras and popular makeup sponges known as beauty blenders. It found that 79% to 90% of the products tested were contaminated with bacteria, including Staphylococcus aureus and E. coli. Beauty blenders, which are often used damp, had the highest bacterial load, according to the study published in the Journal of Applied Microbiology.

Ideally, Sodha said, brushes should be washed after every use, and any type of sponge treated as disposable, but ultimately, the process is “very individual” and people need to figure out what works for them.

Ivy Lee, a Los Angeles-based dermatologist, encourages patients to follow good hygiene practices and build a routine.

“We’re aiming for perfection, but we also don’t want perfect to be the enemy of good,” Lee said.

Stacie Thomas, a makeup artist and educator in Seattle, said she does a deep clean of the brushes and sponges she uses on herself weekly. In between washes, she recommended spot-cleaning after each use with a sprayable instant brush cleaner.

If a weekly wash isn’t possible, Suozzi suggested setting aside time twice a month. She noted that people shouldn’t worry about sticking to a schedule if they haven’t been using their brushes or sponges. But if those tools are in storage, it would be wise to wash them before use.

“It’s pretty laborious if you actually try to clean all your makeup brushes,” she said. “How you clean them matters, too.”

Experts generally recommend using a gentle facial cleanser and water to wash brushes and sponges. The cleanser should be the same one you use on your face, Lee said. “Keep it simple. What’s safe and gentle on your face is safe and gentle for your products.”

Beauty blenders are often more challenging to clean than brushes, Sodha said, because their dense, absorbent material can make it difficult to gauge how well they have been cleaned.

“There’s no way to guarantee how effectively you’re removing the bacteria from these blenders,” she said, and you’ll probably have to judge cleanliness by looks.

Lee said beauty blenders should return to their original color and shape after a good washing. Noticeable signs of wear, like missing chunks or a dull tip, are signs the sponge should be thrown out. Another way to mitigate cleanliness concerns is to purchase cheaper sponges that can be replaced every one to two weeks, Suozzi said.

Brushes should be washed with their tips pointed down to minimize the amount of water that collects where the bristles meet the base because mold can form there, Suozzi said. Avoid wringing out a brush after washing, which can damage its bristles, Lee said. Instead, gently squeeze to draw out as much water as possible.

To dry brushes, arrange them around a sink with the bristles hanging over the edge, Suozzi said. Lee said she lays her brushes out to dry in the sun and will check that they have completely dried by doing a light brush on a clean hand to feel for any residual dampness.

Clean brushes and sponges should be stored away from any dirty tools. “Be careful popping a dirty brush right into the middle of all your clean brushes unless you’re prepared to wash all of them again,” Sherber said.

Experts stressed that it is equally important to keep track of product expiration dates. According to the Food and Drug Administration, there are no U.S. laws or regulations that require cosmetics to have specific shelf lives or expiration dates on their labels. But products often indicate a suggested time frame on the packaging, denoted by a small icon of an open jar with the number of months written inside.

“That clock starts ticking when you begin to use the product,” Sherber said, adding that she frequently tells patients “makeup really shouldn’t celebrate a birthday.”

Liquid formulations, particularly eye makeup such as mascara and eyeliners, have the shortest shelf life. Mascara, for instance, should be replaced every three to six months, Suozzi said, whereas powder products can last one to two years. Even unopened cosmetics can go bad, she said, noting that if you’ve had a product longer than three years, it should probably be tossed.

Lee and Sherber recommended keeping a permanent marker handy and writing on products when they were opened. Thomas suggested familiarizing yourself with the texture and smell of a fresh product, so you can tell when something needs to be thrown out.

“If the texture goes, like, a little dryer or starts going a little patchy, or if your lipstick starts to smell like crayons, that’s how you know it’s time,” she said.

There are also ways to maximize the longevity of some cosmetics by reducing the potential for contamination, experts said. Sherber suggested using stick products where the top layer can be cut off. For loose powders, sprinkle some out on a tissue instead of repeatedly sticking a brush or sponge directly into the container and creating a “cauldron of yuck,” Thomas said.

Though it may be frustrating to get rid of unopened or seldom-used makeup that you spent money on, Sodha said it’s important to take stock of what you truly need and use.

“It isn’t just that the product becomes less efficacious” over time, she said. “There’s actual harm to it at a certain point, and you just want to avoid that if you can.”