Young holiday shoppers who pick out their gifts online have a little secret. More and more, they like to slip in a purchase or two for themselves as they pick out sweaters and gadgets for everyone else. And only a few brands, such as Nordstrom’s and Amazon, are taking the cue.

A new survey by brand consultancy Kelton Global shows self-gifting is becoming an integral part of the Christmas shopping experience, and Millennials are leading the charge. About three-quarters of all shoppers said that when they are online buying clothes, shoes and electronics for others, they also like to get a little something for themselves, according to the survey. Of that group, shoppers under 35 were 40% more likely than Gen Xers or Boomers to self-gift.

PricewaterhouseCoopers backs that up. Millennials spend almost double the proportion of their overall holiday budget on themselves as older shoppers, per PwC’s 2015 Holiday Outlook.

Brands that target Millennial consumers should be taking this trend into account in their holiday campaigns, but often they miss the mark, said Chiara Baldanza, marketing associate at Kelton Global. "While ‘Treat yourself’ messaging is ideal for Millennial-focused active apparel brands, like Under Armour or Lulumenon, instead, their websites focus on buying for others," he said.

While it’s hard to blame retailers for embracing a selfless holiday message, at least some brands are adjusting their tone. For example, the first image on Nike’s home page in early December was decidedly non-gift-oriented: an Air Max sneaker with copy exhorting the user to "run the streets in the Nike Air Max 2016."

"Gifting is still promoted by Nike, but the brand markets to the Millennial mindset by featuring a personal item first and gift ideas as secondary," Baldanza said. Nordstrom’s Cyber Monday email campaign and Anthropologie’s Twitter initiative both used almost the exact same wording to express the same sentiment. Nordstom’s was, "One for her, one for you." Anthropologie’s was "one for them, one for you."

Younger online shoppers self-gift more because they tend to be "spontaneous, self-indulgent and crave instant gratification," said Allen Adamson, author and founder of BrandSimple Consulting. "When they are in shopping mode, it is easier to buy more than just the gifts they were looking for, because otherwise they would have to come back and start all over again."

Adamson noted that self-gifting is usually an online behavior, rather than an in-store one. "Millennials tend to be task-driven in stores, but browsing online late at night, in the private [domain] of themselves and their screens, their true spontaneous behavior comes out," he said.

Also, "for the younger set, useful is the new cool," said Jeff Fromm, president of FutureCast, a Millennial marketing consultancy. "They put together a wish list and figure that if they don’t get everything on their list, it’s easy to go online and buy the remainder for themselves."

Adamson said the job for marketers is "to take the edge off, alleviating any guilt consumers may feel from spending money on themselves instead of others." For instance, Amazon recently tweeted, "Because even if you’ve crossed off everyone on your list, it’s always OK to #treatyourself. "

The Kelton findings, however, say guilt is hardly an issue.

"Our research suggests Millennials don’t feel guilty and don’t think they need permission from brands to self-gift," Baldanza said. She pointed to Stitch Fix, a small online apparel retailer that took the perfect tone with an email promo aimed at young women headed, "Go on … Treat yourself."

Fromm agreed. "Lots of these young consumers are not in traditional relationships with young children to buy gifts for," he said. "They have jobs and self-gift because they figure they deserve a reward."