How Bad Is It Really to Re-Wear Dirty Workout Clothes?

Let's talk about something that we've all probably done before but don't like to admit. No, we're not talking about skipping your warm-up or eating food that's been sitting out for a little too long (though those things definitely fit the bill). We're talking re-wearing dirty workout clothes.

There are so many reasons you may be tempted to re-wear gym clothes after sweating in them once (or twice) already. Maybe you don't have time for laundry, or you want to cut back on how often you have to go to the laundromat. Or maybe you just don't see the point in washing your expensive leggings after just wearing them for a quick 20-minute workout.

Whatever the reason, you may be wondering how bad it really is to put the same clothes back on a day or two later before washing them. Here's what experts have to say.

It's not the most comforting thing to think about, but we all have microorganisms naturally living on our skin — millions of them, actually, just comfortably chilling there all the time, says Teo Soleymani, MD, a board-certified dermatologist at UCLA Health. "This is what we call our skin's microbiome," he says. It includes bacteria, fungi and yeast (a type of fungi).

When you work out, those bugs can transfer to anything you touch, and that includes the clothes you're wearing.

"When we're exercising, we're obviously sweating and wearing clothing that can absorb whatever we're excreting," says Zain Husain, MD, a board-certified dermatologist at New Jersey Dermatology & Aesthetics. "These microorganisms can remain on that clothing after our workouts, especially if we throw them in the hamper. Bacteria and fungus love these dark, damp areas to grow."

You can also pick up bacteria from using shared gym equipment. A January 2019 study in ​BMC Infectious Diseases​ swabbed multiple surfaces in different types of fitness facilities and found that all of them were contaminated by Staphylococcus aureus (known as staph) and MRSA — a type of Staphylococcus aureus bacteria that, according to the Centers for Disease Control and Prevention, is resistant to several antibiotics and is much harder to treat than your standard staph infection.

In normal quantities, these bugs are actually essential for maintaining your skin's balance. So are certain yeast and fungi. But when your clothes get sweaty and warm, you create the perfect environment for those little guys to proliferate faster than normal.

"As we wear our clothes over and over again, one of the things you worry about is having increased quantities [of microorganisms], which can lead to things like irritation, boils, pimples and even abscesses," Dr. Soleymani says.

The problem isn't that the germs exist, but damp environments, like sweaty gym clothes sitting in a hamper, can promote their growth in amounts that make them potentially dangerous.

There are two important factors to consider, says Elizabeth Nieman, MD, a board-certified dermatologist and assistant professor at UNC Chapel Hill: What workout clothing are you talking about? And how sweaty did you get?

Anything that's farther away from your skin is generally less problematic to re-wear. "Re-wearing a running windbreaker is totally different than re-wearing your socks," Dr. Nieman says. "The clothing you wear closest to your body gets the most sweat into it and has the most contact with skin, so it's very important to wash after each use." Think: socks or sports bra.

The absolute worst thing to re-wear is underwear, Dr. Husain says. It tends to collect the most microorganisms, as it is in contact with your genitals and anal area, he says. "If we're trying to compare different clothing to reuse, I'd say definitely not your underwear."

Some fabrics can also be better than others. Dr. Husain says that synthetic materials, such as polyester, tend to have more potential to trap some of these microorganisms.

In fact, a small November 2014 study in ​Applied and Environmental Biology​ found that synthetic fabrics had more unpleasant odors and promoted the growth of certain bacteria more than cotton fabrics.

That feels counterintuitive because synthetic fabrics wick sweat — and theoretically, there could be some truth to the idea that clothing that dries quicker may promote less microorganism growth, Dr. Soleymani says. But the research in this area is lacking so far.

After thinking about the clothing you're considering re-wearing, think about how sweaty you got wearing it.

"If you wear a sports bra and didn't end up getting too active and you want to dry it out and put it back on the next day, that's different than wearing a saturated sports bra and putting it back on the next day," Dr. Nieman says. "If it's mildly sweaty and you let it dry and it doesn't have a lot of odor, then you're probably OK to re-wear it."

Speaking of airing it out: Hanging up your workout clothes to dry may decrease the risk of fungus overgrowth, Dr. Soleymani says. "They love moisture," he says. Bacteria like staph and MRSA are a little more resilient, and may not be deterred so easily. But more airflow can't hurt.

Whether you decide to re-wear dirty workout clothes or not, here are some things you should know about reusing gear in your exercise wardrobe.

Just having an increased number of bacteria on your skin isn't necessarily enough to cause an infection. "But oftentimes all it takes is one little injury or portal of entry," Dr. Soleymani says. We're not talking a huge wound or obvious cut — your run-of-the-mill exercise-induced chafing can compromise the skin barrier enough to let things like staph and MRSA inside, he says.

Staph can cause a mild skin condition called folliculitis, Dr. Nieman says. According to the American Academy of Dermatology Association (AAD), folliculitis is basically an infection in the hair follicles. It happens when something — like chafing, tight clothing or even shaving — damages the hair follicle and creates an entryway for microorganisms.

"It's usually not dangerous, but it can be uncomfortable and unsightly," Dr. Nieman says. Folliculitis looks like a red bumpy rash, and oftentimes it's confused for acne. The good news is that it can easily be treated with a few skincare strategies, like applying a warm compress several times a day and avoiding shaving and waxing, according to the AAD.

But in a more extreme scenario, staph and MRSA can cause deeper infections and abscesses that require antibiotic treatment to clear up, Dr. Nieman says. "We've seen that in a lot of athletes and it pulls them out of their activity while they get treated with antibiotics."

Some bacteria can also promote acne. If your dirty clothes are full of bacteria and oils from your skin, you can end up with clogged pores and an acne flare on your chest or back, Dr. Nieman says.

Fungal infections are also more likely to develop in moist environments. "Athlete's foot and jock itch both have a higher likelihood of developing when you re-wear clothes," Dr. Soleymani says. They're both caused by the overgrowth of fungus, and can be uncomfortably itchy.

Malassezia and tinea versicolor are two other types of fungal infections that Dr. Nieman says can develop when normal fungus on your skin grows unchecked. "Staying in wet clothes can promote these and cause an unsightly rash," Dr. Nieman says.

Overgrowth of certain fungus or bacteria can also cause a skin condition called intertrigo, Dr. Nieman says, which is most commonly caused by candida, a type of fungus, and develops in warm, damp areas of the body where you have skin rubbing against other skin, like the armpits, backs of the knees or any other skin folds, according to the U.S. National Library of Medicine.

"You can get chafing and chronic skin irritation from that as well," Dr. Nieman says. Intertrigo causes red patches of irritated skin and in some cases, can also cause a bad odor.

Even just the minerals that build up on your clothes when you sweat can cause skin irritation, Dr. Soleymani says.

"Sweat consists of different salts — sodium chloride, potassium chloride, things like that. You might notice your colored clothes have a kind of white flaky tinge to them when you air dry after an especially sweaty workout. That's the mineral salts from your sweat. Salts are technically metals, and when they sit on the skin, they can be pretty irritating and cause chafing in areas of repetitive friction," he explains.

Sweat build-up is annoying on its own, but it can also create those micro-tears in the skin that allow bacteria to settle and cause infections.

And finally, sometimes dirty workout clothes just smell. It's not the sweat itself that smells, Dr. Soleymani says, but the bacteria that are feeding on the sweat. "If clothes start to smell, there's a sign there are organisms growing on them," he says.

Re-wearing dirty workout clothes is not a great habit to get into, but for most people, it's not that likely to cause serious issues if you do it every now and then.

You can reduce your risk of getting a skin infection from dirty gym clothes by hanging them up to dry out between workouts and only re-wearing clothes that got minorly sweaty. You can also do a quick wash right in the sink, Dr. Nieman says, and then hang to dry if you plan to re-wear something.

Also, the sniff test is your friend. "If it smells, it's probably not a good idea to re-wear it," Dr. Soleymani says. "Give it the sniff test, and if you think it needs to be washed, it probably needs to be washed."

If you do choose to re-wear dirty gym clothes every now and then, make sure to keep tabs on your skin. "If you're noticing skin irritation or chafing, then definitely get your clothes in the wash," Dr. Nieman says.

It's also really important to take off wet clothes after you work out and not sit in them all day long, Dr. Nieman says. Changing into dry clothes and showering immediately after a workout (or at least using a body wipe until you can) can help minimize skin infections and body odor, even if the clothes you sweated in were a little less than fresh.