To keep his body odor in check, he takes a daily shower with an unscented Dove body wash, usually after the gym. But Mr. Felix, who is in his early 30s and doesn’t want to be taken for a hippie, is cautious about disclosing that he doesn’t wear underarm protection to people he dates. “When you tell a person you don’t wear deodorant, you come across as, ‘Oh, how European, how natural, how funky,’ ” he said.

The few times Mr. Felix has mentioned on a date that he goes without deodorant, he said, things have quickly turned, well, sour. “It’s weird, but I don’t smell,” Mr. Felix will announce. Then, he said, “the comment is always, ‘You think you don’t smell.’ ” (Mr. Felix admitted that he lives in horror of having the rare fetid day.)

But Matt Merkel, an engineer from Birdsboro, Pa., is sure he smells just fine. How? Recently, Mr. Merkel, 29, told his mother and sister that he gave up the old Speed Stick as a teenager, and they were shocked. “I was like, ‘Smell me, I don’t care!’ ” he told them, adding, “They probably just thought I was still 13 or 14, and doing that because somebody told me to.”

America’s custom of rigorous cleanliness was in full swing by World War II, at which point most homes had acquired a full bathroom, said Ms. Ashenburg, the author of “The Dirt on Clean,” and intensified with postwar marketing efforts. But standards are relaxing, at least in some corners. An article in Parenting magazine’s November issue suggests that stressed mothers need not shower daily, stating reassuringly: “The air is drier in the winter, which means you need your skin’s natural lubricants.”