The rise in popularity of athletic wear and relatively genderless offerings from companies like North Face and Patagonia have also helped spread unisex design. Footwear brands like Converse, Vans or Birkenstock also now market the same styles for both men and women. Wearable technology, like smartwatches and activity monitors, has been relatively gender-neutral.

”If a guy wants to go out and buy a woman’s scarf and thinks that’s fashionable, whatever his sexual preference, it’s going to happen,” said Marshal Cohen, chief industry analyst at the New York-based research firm NPD. “This is something where the world jumped way ahead of retail, and now retail is trying to catch up.”

Still, the most significant shifts in gender categorizing — and certainly the most debated — have been in children’s merchandise. The shifts stem from a growing recognition, first among niche outlets and now among mainstream companies, of the role many traditional toys, clothes and costumes have played in reinforcing gender stereotyping. Experts have linked the items to all manner of gender disparities, including gaps in boys’ and girls’ self-confidence levels and career choices.

Parents have taken to social media to protest retailers’ overly girly offerings, or to show off their children defying gender norms. Last year, Land’s End introduced a line of science-themed shirts for girls after a New Jersey mother, Lisa Ryder, posted an open letter on the brand’s Facebook page calling out its boy-only science collection. More recently, a Virginia father, Paul Henson, garnered widespread kudos online for his Facebook post about his 3-year-old son, who intends to dress as Elsa from Disney’s “Frozen” movie this Halloween.

Target’s move to remove gender labels from its toy section came after Abi Bechtel of Ohio took to Twitter to protest a sign on display at the retailer for “Girls’ Building Sets.” Target announced in August that it was removing gender-based signs from its children’s toys and bedding aisles.

The retailer’s online store still labels girls’ and boys’ toys, however, because its data suggests that many shoppers on the site still search for products by gender, according to a spokeswoman, Molly Snyder. (The site does allow shoppers to search for gender-neutral toys.)

Toys “R” Us has not categorized girls’ and boys’ toys in its stores for some time, said Richard Barry, the retailer’s global chief merchandising officer. “What we’re seeing is that there are different play patterns that appeal to different kids, and gender lines are not necessarily what drives that,” Mr. Barry said.