Knickers, undies, banana hammocks — whatever you call your underwear, it’s an integral part of (almost) everyone’s wardrobe. And the variations are endless.

Some people have a lucky pair, period panties, comfy granny panties for a night in, and some for special occasions. (Hellooo, date night!)

Silly nicknames aside, we take underwear very seriously, judging by the money we spend. Industry experts estimate that U.S. lingerie spending will hit $11.36 billion by 2025. Holy Underoos — that’s a lot of money for items of clothing that are hidden from view (most days).

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Despite our investment in these small squares of fabric and the fact that our “delicates” contain our most delicate anatomy, there’s a lot we don’t discuss about underpants from a health perspective.

Never fear — we’ve asked experts all the tough (and awkward) questions, from what to wear at the gym to what to do if you’ve run out of clean laundry.

1. How bad is it to do a second day in the same undies?

We have good news for anyone who’s skipped a laundry day: As far as health is concerned, it’s not a huge issue to wear the same pair of underpants 2 days in a row, says J. Scott Kasteler, MD.

That is, as long as those undies are clean to the eye (unmarked with urine or stool). From a health standpoint, you could go several days without a fresh pair, Kasteler says.

But before you wear your “Monday” pair on Tuesday, consider two important exceptions.

If you have any scratches, sores, or rashes on your skin, don’t stretch the mileage on your underwear or you could end up with an infection. And if you’re breaking a sweat, it’s best to don a fresh pair. For folks with vaginas, moisture buildup in the nether regions can lead to yeast infections.

While those with penises may not be as susceptible to infections, it’s still a best practice to keep the area nice and dry. It’s just not worth the risk of chafing below the belt. (Hey, there’s a reason swanky gyms have spare pairs for sale.)

2. Does fabric matter?

The quick answer is yes. Your underwear fabric can make a difference for your health.

To prevent no-fun down-south issues like rashes, vulvovaginitis (an infection in the vagina or vulva), or jock itch, health experts suggest wearing new, clean, well-fitting pairs of cotton underwear to allow for breathability and to absorb moisture that can be a catalyst for infection.

Fabric that wicks away moisture has also become popular as a base layer for outdoor athletes, especially during the winter.

Underwear with wicking fabric (polyester or a polyester blend) can reduce moisture in your neither regions during long days on the slopes (or when you’re just huffing it to the train).

A small 2015 study found that people who wore these synthetic fabrics saw improved athletic performance and comfort over wearing cotton fabrics.Hooper DR, et al. (2015). Synthetic garments enhance comfort, thermoregulatory response and athletic performance compared with traditional cotton garments. DOI: 10.1519/JSC.0000000000000783 (If you’ve ever run a marathon in a cotton T-shirt, you’ll understand why this makes sense.)

But it’s still a good idea to change your undies after a sweaty workout to minimize the risk of infection.

3. Is it OK to work out in a thong?

Ouch? Maybe. While studies linking thong-wearing at the gym to health consequences are limited, you may want to be careful about putting these babies on before hitting the treadmill.

Some docs feel that thong underwear has the potential to cause some trouble if you’re prone to repeated vaginal infections. Thongs easily shift around (think back to front), and bacteria can go along for the ride.

A 2019 survey indicated that thong underwear may not actually be associated with increased infections, but it didn’t address usage during intense activities like working out.Hamlin AA, et al. (2019). Brief versus thong hygiene in obstetrics and gynecology (B-THONG): A survey study. DOI: 10.1111/jog.13958

Thongs also expose your parts to other pieces of clothing — like, say, sweaty leggings — that could trap moisture and, again, increase the odds of infection.

For comfort and support, and to err on the safe side, get undies with full booty coverage.

4. Which is really better: Boxers or briefs?

Boxers and boxer briefs are popular with all genders. But if you have testicles, there are some factors to consider.

Fashion and comfort level aside, the real debate between boxers or briefs is centered on sperm production and increasing (or decreasing) your chances of conceiving.

Research points to heat (scrotal temperature, if you want to get specific) as a major factor in sperm production.dos Santos Hamilton TR, et al. (2016). Evaluation of lasting effects of heat stress on sperm profile and oxidative status of ram semen and epididymal sperm. DOI: 10.1155/2016/1687657 And what keeps your testicles tightly packed away and warm and toasty? You got it: underwear.

Experts suggest staying away from tight-fitting underpants (and saunas and hot tubs) if you’re actively in the baby-making business.Mínguez-Alarcón L, et al. (2018). Type of underwear worn and markers of testicular function among men attending a fertility center. DOI: 10.1093/humrep/dey259 Otherwise, you’re probably fine with whatever is comfortable.

5. Should I go commando?

Going commando, aka no underpants, on occasion (how cheeky!) is likely more common than you think. And it turns out there are a couple of good reasons to “forget” to don a pair, especially when sleeping or even at the gym.

There’s more airflow, and you could sleep a little cooler, both of which can be good things.

You’ll want to watch out for tight outer clothing if you’re going sans undies during the day. And you’ll likely have to wash your pants more often. The general rule is that if something that touches your bare bum, you should wear it only once between washes.

If you have no skin issues (rashes, razor burn, etc.), then no undies is no problem. Enjoy the freedom and the ventilation.

Bottom line (pun intended): Keep your underwear clean, dry, and fresh (and fun!). If your skin is healthy and you’ve kept your undies clean, then wearing them a second day is A-OK, so long as you’re not breaking a sweat.

During exercise, wicking fabric can be a big help, especially if you’re prone to infections down there. Look for underwear made from a synthetic-blend fabric that will pull moisture away from your body.

Thongs are debatable, especially at the gym, where your skin is more likely to make contact with moisture- and bacteria-laden outerwear that could lead to infection.

And lastly, going commando can be just fine, as long as you’re keeping your skin clean and the rest of your clothing as clean as those unworn undies.