Cookie syncing (also called cookie matching) is a process where two or more advertising platforms share and align their user identifiers. Since each platform sets its own cookies when a user visits a website, syncing allows them to match these separate identifiers to recognize the same user across different domains or systems. This enables unified tracking and personalized advertising across websites.

Why It Raises Privacy Concerns

Cookie syncing plays a major role in real-time bidding (RTB) and programmatic advertising, but it poses serious privacy risks. It often happens without the user’s knowledge or consent, enabling widespread tracking of user behavior across the web. Because personal identifiers can be linked and distributed through ad networks, users may lose control over how their data is used. Under GDPR and ePrivacy laws, cookie syncing is considered intrusive and requires explicit, informed consent.

Compliance and Risk Mitigation

To stay compliant:

• Organizations must obtain clear consent before initiating any cookie syncing.

• CMPs (Consent Management Platforms) should track user preferences accurately and enforce restrictions.

• Companies should audit third-party cookies on their site to identify syncing behavior.

• Where possible, adopt privacy-preserving alternatives like contextual advertising or server-side tracking with proper safeguards.

Reducing reliance on cookie syncing not only improves privacy compliance but also builds user trust in a privacy-first digital environment.