Every time you reject internet cookies, there may be a bigger cost than you realize. A new Boston University study finds that removing third-party cookies slashes publisher revenue by more than a third — and that privacy-friendly alternatives barely help.
That pop-up asking whether you want to accept internet cookies has become one of the most familiar — and most ignored — moments of modern online life. But a new study from Boston University suggests the decision carries real economic weight, and reflexively hitting “reject” could quietly erode the free, ad-supported web that most people rely on every day.
Published in Proceedings of the National Academy of Sciences, the study analyzed roughly 200 million ad impressions worldwide and found that blocking third-party cookies — the kind placed by advertisers rather than the websites you visit — reduced publisher ad revenue by more than a third. In the European Union, where online privacy regulations are stricter, that revenue loss climbed to 66%.
“Internet cookies—especially third-party cookies—have been central to how online advertising works,” corresponding author Garrett Johnson, an associate professor of marketing at the BU Questrom School of Business, said in a news release.
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,” Johnson added.
The European Union has tougher online privacy rules than much of the rest of the world.
Why Cookies Matter to the Web’s Economy
Cookies help advertisers identify users as they move across different websites, allowing them to target ads more precisely and measure which campaigns are actually working. That efficiency translates into more advertising dollars flowing to the content creators, news sites and publishers that make up the open web.
“If more users decline cookies, it would likely reduce the effectiveness of digital advertising and the revenue that supports much of the open web,” added lead author Zhengrong Gu, a doctoral candidate at the Questrom School of Business.
The tradeoff, of course, is privacy. Wayne State University researcher Elizabeth Stoycheff has written that Website cookies are online surveillance tools,
noting that the commercial and government entities that use them would prefer people not read those notifications too closely.
The discomfort many users feel is legitimate — cookies do enable persistent tracking across the internet.
In response to growing privacy concerns, the industry has explored alternatives. Paywalls, subscription models and cross-site login systems have emerged as workarounds. Tech companies have also experimented with privacy-enhancing technologies, or PETs, designed to serve advertisers without exposing individual browsing histories.
Google’s Privacy Sandbox Fell Short
The most prominent PET experiment was Google’s Privacy Sandbox, a six-year initiative that ultimately collapsed in 2024. One of its tools shared a user’s general interest categories with advertisers rather than detailed browsing histories — a promising concept in theory. In practice, the BU researchers found it barely moved the needle.
“In our study, Privacy Sandbox recovered only about 4 percent of the revenue lost when cookies were removed,” added co-author Shunto J. Kobayashi, an assistant professor of marketing at the Questrom School of Business.
Kobayashi attributed the weak performance partly to low adoption rates and partly to “technical frictions, especially slower ad loading times” that changed the user experience in ways that hurt ad performance.
The researchers write in their paper that their findings, alongside 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.
How the Study Was Conducted
To test these effects in a real-world setting, the team used data from ad management firm Raptive and drew on a large-scale experiment conducted by Google and overseen by the UK’s Competition and Markets Authority. Around 60 million desktop and mobile Chrome users were randomly assigned to one of three conditions: cookies enabled, cookies disabled, or cookies replaced by Privacy Sandbox.
“The experiment created a rare opportunity for independent, large-scale evaluation open to external participants,” Johnson added.
What This Means for Students and Regulators
For college students who grew up online and consume enormous amounts of free digital content — from streaming platforms to news sites to niche blogs — the stakes are concrete. If advertising revenue dries up, the free content model that much of the internet runs on becomes harder to sustain.
The findings also carry policy implications. As regulators in Europe and beyond consider tightening online privacy rules even further, Johnson argues the economic evidence deserves serious weight.
“Our results provide unusually strong evidence—from a global, industry-wide field experiment—that restricting cookies carries significant economic downsides that regulators should consider,” added Johnson.
As for his own browser habits, Johnson does not shy away from the question.
“From my perspective, accepting cookies creates substantial benefits for the advertising ecosystem and the publishers I care about,” he said, “with what I perceive to be little personal risk.”
Source: Boston University