It’s a choice you may face multiple times a day—and, at this point, your reaction is probably reflexive. Are you going to accept those internet cookies, reject them, or spend a little time customizing your settings?

Increasingly, internet users are pushing back against cookies—the digital crumbs used by websites and advertisers to spot returning customers—by choosing privacy-enhancing browsers or clicking that reject button. But ditching the cookies may have big implications for the free web. If digital companies, content creators, and advertisers aren’t making money from our surfing, the quality and usefulness of the products they offer might suffer too.

In a new study, Boston University researchers highlight the potential impact the loss of cookies has on advertisers and how alternative systems designed to balance privacy and revenue fail to recoup the costs.

They analyzed 200 million ad impressions—or views—worldwide and found that removing cookies cut website publishers’ revenue by more than a third. They also discovered that privacy-enhanced alternatives, notably a major Google project called Privacy Sandbox, only clawed back a small portion of that lost revenue. The findings were published in PNAS, the National Academy of Sciences’ flagship journal.

“Internet cookies—especially third-party cookies—have been central to how online advertising works,” says Garrett Johnson, a BU Questrom School of Business associate professor of marketing. Third-party cookies are those placed by an organization, like an advertiser, not connected to the site you’re on. “In our study, removing third-party cookies reduced publisher ad revenue by about 35 percent—and about 66 percent in the European Union—showing that cookies still play a major economic role in supporting the open web.” The European Union has tougher online privacy rules than much of the rest of the world.

According to Zhengrong Gu, a Questrom PhD candidate, because cookies help advertisers spot users around the web, they can better target and measure their ads. That makes advertisers’ spending more efficient, putting more ad money in the pockets of content creators and publishers. “If more users decline cookies, it would likely reduce the effectiveness of digital advertising and the revenue that supports much of the open web,” says Gu (Questrom’26). 

The downside of cookies: no one really likes being followed. “Website cookies are online surveillance tools,” wrote Wayne State University researcher Elizabeth Stoycheff in a Conversation article, “and the commercial and government entities that use them would prefer people not read those notifications too closely.”

There have been a couple of different responses to the decline in cookie use. One is the implementation of paywalls and subscriptions to keep the cash flowing; another is requiring customers to use log-ins that work across multiple sites. Tech companies are also experimenting with privacy-enhancing technologies (PETs) that try to balance advertising needs with user privacy concerns. One of the best known PETs is Privacy Sandbox, Google’s now-defunct six-year experiment in cookie alternatives, which included innovations such as a browser tool that shared a customer’s interests rather than their detailed online history.

“In our study, Privacy Sandbox recovered only about 4 percent of the revenue lost when cookies were removed,” says Shunto J. Kobayashi, a Questrom assistant professor of marketing. That weak impact was in part due to the limited adoption of the new tools and because they changed the user experience, he says, introducing “technical frictions, especially slower ad loading times.”

In their paper, the researchers write that their findings, alongside those from other studies, “informed Google’s decision to abandon its plan to replace cookies with Privacy Sandbox. The episode underscores the difficulty of aligning privacy, performance, and competition goals in digital markets.”

To examine privacy technologies in a real-world setting, the BU team used data from ad management firm Raptive, and leveraged an experiment conducted by Google and overseen by the United Kingdom’s Competition and Markets Authority. During the study, Chrome users were randomly assigned to one of three groups: cookies-enabled, cookies-disabled, or cookies replaced by Privacy Sandbox. The study included around 60 million desktop and mobile Chrome users.

“The experiment created a rare opportunity for independent, large-scale evaluation open to external participants,” says Johnson, an expert on digital marketing who has studied privacy regulations, online ad effectiveness, and the economics of digital advertising. 

He adds that many European regulators are considering even tighter online privacy rules, which could have a negative impact: “Our results provide unusually strong evidence—from a global, industry-wide field experiment—that restricting cookies carries significant economic downsides that regulators should consider.”

As for users faced with that daily accept or reject decision, Johnson recognizes that everyone will make the call that works for them—but he leans toward clicking “accept.”

“From my perspective, accepting cookies creates substantial benefits for the advertising ecosystem and the publishers I care about,” he says, “with what I perceive to be little personal risk.”