Keene is one of a growing number of men who share concerns that polyester-based shorts and underwear could be harming their fertility, hormones and general health, and who are looking to clothe their most sensitive areas in natural fibers in response.

Though natural-fiber undergarments have been around for years—big-box brands such as Hanes and Calvin Klein sell boxers and briefs marketed as 100% cotton—new companies including Ryker are upping the ante, eagerly marketing their products to men increasingly interested in self-optimization.

Much of contemporary men’s underwear is made from polyester-based fabrics, which are themselves derived from petroleum. Men avoiding these fabrics have two main concerns. One is that synthetic fabrics, when washed, shed “forever chemicals” and microplastics that recent studies have found present in all manner of human organs. The other is an anxiety that nonnatural fibers negatively affect male fertility.

Dr. Paul Turek, a reproductive urologist and micro-surgeon in California who specializes in male fertility and sexual health, said he’s hearing these sorts of worries from his patients increasingly often. “Microplastic conversations are constant now,” he said. And while he tells patients that reducing plastic exposure is generally advisable, he hasn’t yet seen research to validate fears that their shorts are harming them. Instead, he sees these worries as “the latest in a long line of men’s concerns about fertility that aren’t always supported by concurrent science.”

For years, men have projected the anxieties of the day onto their underwear. Concerns about the relative impact of boxers and briefs on fertility, for instance, have given way to today’s murmurs about plastic, testosterone and population rates. “We’ve been dealing with underwear and men’s concern about their fertility for my whole career and I’m gray now,” Turek said.

The rise of natural underwear can be attributed in part to the growing conversation about male wellness and fertility, much of it on social media and podcasts. “I could be talking to a 60-year-old man, or I could be talking to a Gen-Z person like myself, and they’ll be like, ‘Oh, you know, I think I’ve heard about something like this,’” Ryker founder Garrett Wilson, 26, said. For influencers and podcasters who discuss sometimes novel techniques to optimize health and fitness, underwear is the latest in a line of favorite topics, after things such as protein intake, sunlight exposure and seed oils. “I think polyester now is maybe what seed oils were in 2020, 2021,” Wilson said.

For many men, any shred of possibility that their shorts and underwear can negatively affect their health makes a change worth it. Caden Zrubek, 25, made the change after struggling with Lyme disease and exposure to toxic mold, and remains concerned about the potential impact of polyester on health and fertility. He prefers the peace of mind that he gets from wearing natural fibers. “My point of view is, why would you even risk it?” he said.

Outdoor companies have long sold wool undergarments to hikers and campers, who love them for their odor and temperature regulation. That’s initially why Aaron Valenzuela, 40, an artist in Los Angeles, bought them. But after reading about the possible negative effects of plastic on testosterone, he started wearing his camping underwear more regularly. “I don’t want to be on testosterone boosters when I’m an old man,” he said. 

Many of the brands that have popped up to serve this market come from founders looking for their own non-polyester clothing. In late 2022, Chance Landesman launched Unbleached Apparel, a company that produces garments including underwear made from untreated cotton. It had been easy enough to find underwear marketed as 100% cotton, but he knew that the number typically refers to the body of a pair of underwear—not its waistband or the thread that holds the product together. “That was sort of a wake-up call,” he said. He called up representatives for a few brands to ask whether their cotton underwear was sewn with polyester thread, but couldn’t get an answer that satisfied him. When Landesman subjected ostensibly cotton pairs he purchased to a “burn test,” used to identify a fabric’s fiber content, he says he found the presence of other, non-cotton materials. 

He now sews most pairs of Unbleached Apparel underwear by hand in his Brooklyn studio, at a rate of about one pair every 30 minutes.

At the more style-conscious end of the spectrum is EDN, co-founded by Mac Boucher (a creative director whose sister is the musician Grimes) and fashion-industry veteran Matthew Domescek. EDN’s website, with its elegantly art-directed photoshoots, is meant to appeal to discerning shoppers who want to apply the same scrutiny to their clothes as they do to the things they eat. Customers receive a card explaining the provenance of their “health-enabling” undies, including the locations where the fiber is grown, milled into fabric, dyed and sewn. 

Organic cotton and merino wool are more expensive than polyester blends, and the non-poly sewing thread that Landesman prefers can’t run through industrial sewing machines at the same high speeds as its polyester counterpart. All this means that going natural costs more money: a pair of Landesman’s unbleached boxers start at $35, while Ryker’s boxer briefs sell for $34 and up and EDN’s go for $38.

But as Myles Snider, who works for a fintech company in New York, realized when he switched to wool and cotton shorts and underwear about five years ago, high-end polyester-based gear isn’t always more affordable. Switching to natural fibers didn’t necessarily carry an outsize cost. “Athleisure shorts and underwear have gotten really expensive in recent years. For the most part, you can find good cotton or wool shorts that are the same price or significantly cheaper,” he said. Men, it seems, are willing to put their money where their balls are: Wilson, the Ryker founder, expects his company to clear $10 million in sales this year.

Of course, swapping out polyester underwear isn’t a silver bullet. “If someone’s diet is terrible and they’re not sleeping well and they’re drinking a lot, you should probably start with the basics,” Snider said. “This is definitely up the stack.” But whatever the health benefits, he’s glad to have made the change. “Once I made the switch, I just felt like these products were better across the board,” he said. “They were a lot more durable, a lot more comfortable. And they don’t smell as bad.”