“It sucks all that stuff in,” Ms. Sykes said recently. “It’s so funny that when you take them off you just become a blob. You look in the mirror, and it’s like, hey, now I’m an amoeba.”

The snickering rose a decibel level in February, when Spanx introduced its first products for men. On “Jimmy Kimmel Live,” the host was nearly ejected from his own Handsome Men’s Club after Rob Lowe accused him of wearing Spanx. Cue giggles from the audience and a horrified look from another club member, Matthew McConaughey, his tight abs unexposed for once.

Steve Carell, who received an early sample of a men’s T-shirt, said in a deadpan interview at the Golden Globes, “I have no unsightly bulges but an excellent product I’m sure.” Wink-wink.

The inside joke? Spanx for Men has been a huge retail hit.

“We are selling them as quickly as Spanx can make them,” said Nickelson Wooster, the men’s fashion director at Neiman Marcus, which was until recently the only department store carrying them. (This month Spanx for Men arrived in Bloomingdale’s, Saks Fifth Avenue and Nordstrom, and at Web sites like freshpair.com.) “Men may not be talking about it, but they’re buying it.”

Men’s “shapewear” is “the next big thing,” declared Michael Kleinmann, the president of Freshpair, which sells underwear to both sexes. Already, compression garments from brands like Equmen and Sculptees, to name two, have been selling briskly.

Eighteen months ago, when Freshpair got Equmen’s compression T-shirts, “we sold out,” Mr. Kleinmann said. Men’s torso-enhancing T-shirts are part of a revolution in men’s underwear that has been taking place over the last decade, he said. Another popular but hush-hush product is profile-enhancing underwear, which he called “the equivalent of a push-up bra” for men.

The success of Equmen, an Australian label, is one reason department stores and online retailers have been eagerly awaiting Spanx for Men. At Saks Fifth Avenue, Equmen has been sold for less than a year and has already become one of the store’s best-selling underwear, said Eric Jennings, vice president for men’s fashion at Saks.

“It’s pretty remarkable,” Mr. Jennings said, adding that Equmen is neck and neck with better-known brands like Hugo Boss and 2(x)ist. Its robust sales are even more remarkable considering that Equmen isn’t cheap: tanks are $89, T-shirts up to $109. By contrast, Spanx’s men’s undershirts go for $58, its tanks for $55. The body-sculpturing tops fromRipt Fusion are $58 to $62.

Just as it took time for men to embrace beauty rituals they considered effeminate — remember when moisturizing used to be a metrosexual thing? — so has there been a learning curve for shapewear. “The biggest obstacle is to get a guy to understand it’s a new category, and it’s O.K. to wear it,” Mr. Kleinmann said. “It is still a little taboo.”

Not surprisingly, some bashful shoppers are going online. “We’ve noticed, as good as in-store sales are — and they are good — the online sales are better,” said David Witman, the men’s general merchandise manager for Nordstrom. Men “might be embarrassed to ask for it, but they want it,” he said.

Some clever semantics may help. Mr. Wooster of Neiman Marcus suggested that one way for men to think of a foundation garment (as he called Spanx) is that it is about “problem solving, and another way of feeling secure and prepared for life.”

Stephen Viscusi, a career coach, couldn’t agree more. He thinks that all men over 40 should wear Spanx to job interviews. “When you feel good about the way you look, you interview well,” said Mr. Viscusi, the author of the book “Bulletproof Your Job.”

Although Mr. Viscusi is 39, he wears Spanx T-shirts routinely. He recently wore them to see executives from Bravo and VH1. “It gave me pecs, gave me definition, it gave me confidence,” he said.

Others want to hide more than a growing paunch. Some men have told Mr. Jennings that they’re “self-conscious about their nipples” and buy Equmen tops for camouflage.

And men in their 40s and 50s buy them to look more streamlined, Mr. Jennings said. “Shirts are fitting closer to the body. You want to make your physique look as flattering as it can be.”

Keith Peer, a 43-year-old software executive in Medina, Ohio, owns six Spanx crewnecks, which he credits with improving his posture and helping him look better in tapered shirts. “It enhances your figure, it fits tight, sucks you in,” he said.

Mr. Peer, the chief executive of Central Command, said he was fed up with undershirts that bunched up. With those, he said, you look “like you have a tire around your waist.”

Sara Blakely, the founder of Spanx, said that her products weren’t aimed at men with beer bellies and women with muffin tops. Stars as lean as Gwyneth Paltrow wear Spanx, said Ms. Blakely, who says she was a Size 2 when she invented it. The brand was never for “the hugely overweight,” she said.

Nor are people who buy shapewear necessarily middle-aged. Seventy-five percent of Equmen customers are 37 to 43, according to Corie Chung, a founder. “When men’s bodies start to change and life catches up with them,” she wrote in an e-mail. However, the products can’t work miracles. Some people think that by putting on shapewear “you’re going to shed pounds,” said Michael Vallarelli, a customer service representative atfreshpair.com. It can smooth out a man’s midsection, but “it’s not going to flatten anyone out by any means,” he said.

While women tend to gush about what has been called the “flesh-compressing miracle of Spanx,” men are more likely to point to how super-tight tees relieve their back pain. Robert Hytner, a 51-year-old former defense contracting executive in New York, turned to Equmen shirts after a back injury, and then got hooked because they improved his silhouette. “Whatever garment I put on top, I had a tight look,” he said of his 10 Equmen undershirts. He says his back pain is gone, too.

Still, undergarment trickery has its pitfalls, especially on dates. Men have been known to express surprise when a Spanx-compressed woman disrobes in the bedroom only to reveal a less svelte figure. Now women can complain, too.

“Spanx for Men is all good, until you meet a chick,” one skeptic warned on Twitter. “You gain 45 lbs when you get naked.”