August 9, 2025
2 min read
Third-party cookies, defined as cookies set by domains other than the one being actively visited, have been shown to play a pivotal role in online advertising and user tracking (Kreuter et al., 2020;. Analysis of their deployment reveals several key findings:
Prevalence and Mechanism:
Third-party cookies are most commonly set by ad tech platforms, analytics providers, and embedded third-party applications (e.g., social media widgets, chat services). Their insertion into a user's browser occurs when external content loads on a page, enabling the third party to read and write cookies even though the user is not directly visiting their domain.
Functionality:
The primary uses include:
User Impact and Privacy Concerns:
Empirical studies highlight the significant privacy risks associated with third-party cookies. Users are often unaware of the extent of cross-site tracking, which can result in aggregation of sensitive personal data without explicit consent.
Browser and Industry Response:
Major browsers have begun implementing restrictions or outright blocking of third-party cookies due to mounting privacy concerns. For example, Safari's Intelligent Tracking Prevention (ITP) and Firefox's Enhanced Tracking Protection (ETP) have significantly reduced the reach of third-party tracking.
Key findings highlight:
