`c_user`

Holds the account number you are signed in as. Remove it and Facebook stops recognizing you as logged in.

Owner: Meta Platforms, Inc.
Matches: The exact name c_user
Needed to Work: Yes. Removing it can sign you out or break the site.
Confidence: Verified
Source: https://www.facebook.com/privacy/policies/cookies/?annotations[0]=explanation%2F1_common_cookies_and_uses
Last Reviewed: 2026-09-14

Which Sites

Only on facebook.com, messenger.com and their subdomains. The same name on another site is a different cookie, and is not described here.