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Knickers, undies, banana hammocks: Whatever you call your underwear, it’s an integral part of (almost) everyone’s wardrobe. It comes in all shapes, sizes, styles, and fabrics. Some people have a lucky pair; others buy ones just for special occasions. (Hellooo, date night!) But silly nicknames aside, we take underwear very seriously judging by the money we spend. Industry experts say the global underwear industry is worth $30 billion. Holy Victoria’s Secret! That is a lot of money for a piece of clothing hidden from view (most days).

Despite our investment in these small squares of fabric, and the fact that our “delicates” contain our most delicate anatomy, there’s a lot that’s never discussed 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.

The Revealing Truth About Your Underwear

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

We have good news for anyone that’s skipped a laundry day: As far as health is concerned, there is no issue with wearing the same pair of underpants two days in a row, says Greatist expert J. Scott Kasteler, M.D. That is, so long as those undies are clean to the eye (i.e. 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, there are two important exceptions: If you have any skin scratches, sores, or rashes, don’t stretch your mileage on your underwear, or you could end up with an infection. And if you’re busting a sweat, then it’s best to don a fresh pair. For ladies, moisture build-up in the nether regions can lead to yeast infections. And while men may not be susceptible to the same thing, a best practice would be to keep the area nice and dry as well. It’s just not worth the risk of chafing below the belt. (Hey, there’s a reason swanky gyms have spare pairs for sale.)

Underwear Drawer

2. Does fabric matter?

The quick answer is yes; your underwear fabric can make a difference when it comes to your health. To prevent no-fun genital issues like vulvoganities (infections in the vagina or vulva) or jock itch, health experts suggest wearing new, clean, loose-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 keep moisture away from the neither regions for those long days on the slopes. One study found that participants who wore these synthetic fabrics saw improved performance and comfort over wearing cotton fabrics Synthetic Garments Enhance Comfort, Thermoregulatory Response and Athletic Performance Compared with Traditional Cotton Garments. Hooper, D.R., Cook, B.M., Comstock, B.A., et. al. The Journal of Strength & Conditioning Research. 2014 Dec 1. . (If you’ve ever run a marathon in a cotton T-shirt, you’ll understand why this makes sense.)

Thong Health

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

Ouch? Maybe! While studies linking thong-wearing at the gym and health consequences are limited, you may want to take caution when putting on these babies before hitting the treadmill (or ever). Thong underwear has the potential to cause some trouble if you have any repeat issues with vaginal infections. Thongs easily shift around (think back to front), and bacteria goes along for the ride. It also exposes your lady parts to other pieces of clothing, like, say, sweaty leggings, that could be trapping moisture and, again, upping the odds of infection. Get undies with full booty coverage to avoid these issues.

4. Which is really better: Boxers or briefs?

Fashion and comfort levels aside, the real debate between boxers or briefs is centered on sperm production and increasing (or decreasing) your chances of conceiving. Studies point to heat (scrotal temperature, if you wanna get specific) as a major factor in sperm production. And what keeps your testicles tightly packed away and warm and toasty? You got it: underwear. Experts suggest staying away from tight-fitting underpants if you’re in the baby-making business .

Going Commando

5. Should I go commando?

According to one poll, a quarter of all Americans go commando, a.k.a. no underpants, on occasion (how cheeky!). And it turns out, there’s a couple good reasons to “forget” to don a pair, especially during exercise. Underwear like boxers that fit loose enough to move against the skin can rub and cause chafing during exercise. (Ouch!) If your outer clothing is tight or form-fitting and sweat-wicking, underwear is not needed during exercise, says Kasteler. If you have no skin issues (rashes, razor-burn, etc.), then no undies is no problem! Enjoy the freedom!

The Takeaway

Bottom line (#funpun): Keep your underwear clean, dry, and fresh (and cute!). If your skin is healthy and you 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 any issues—look for underwear that has a synthetic-blend fabric made to pull moisure away from the body. Thongs, however, are a debatable, especially at the gym where your skin is more susceptible to make contact with moisture- and bacteria-laden outerwear that can lead to infection. And lastly, going commando can be just fine, even at the gym, as long as you're keeping your skin clean and your workout clothes are form-fitting and sweat-wicking.

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