Basics of the DEMDEX Cookie - questions related to cookie attributes



We're coming up on some questions about the DEMDEX cookie, not only initial cookie set but subsequent marketing attributes.


  1. When is the cookie is set for a new visitor?  Upon first visit to our website?
  2. What attributes are set on initial creation of cookie?  Is this just the UUID?
  3. Is cookie subsequently written to? And when? And what call does that?  We then see all of our device-based destination partners showing up as attributes of the cookie.


Any insight would be greatly appreciated.


Accepted Solutions (0)

Answers (1)

Answers (1)



Hi Marc,


Audience Manager sets the Demdex cookie to assign a unique ID to a site visitor.


  1. This is set on the first visit on any website which has an Adobe Visitor Id service implemented on their website. So it could be your website or any other. The demdex cookie is set in the third-party, domain, which is separate from the website domain.


  1. Attributes of Demdex cookie
  • The demdex cookie contains a Unique User ID (UUID) as shown in the example below:


  • Lifetime: The demdex cookie has a time-to-live (TTL) interval of 180-days. The TTL is reset to 180-days upon each user interaction with a partner website. The cookie expires if a user does not come back to your site within the TTL interval.
  • Opt-out: Audience Manager resets the cookie with a Do Not Adobe Target string if a user opts-out of data collection. In this case, the cookie TTL is set as 10 years.

To understand the working of calls to Visitor Id service and setting of cookies check the Product document: 

How the Experience Cloud Identity Service requests and sets IDs 






Thank you Rachit. Very helpful. I do understand the demdex cookie on first visit, which contains the UUID.


A short follow-up question for you:


We also notice that as part of the demdex cookie, there are also "advertising attributes" associated with it.  These appear to be our device-based media destination partners - channels like Google Adwords, DCM, etc...  We understand these support the ID syncing, to increase match rate.  Are you aware of such cookie attributes?  If so, do you know when they are set?


Many thanks!


Hi Marc,

The partner id sync happens on the 1st visit itself. 


The following steps describe how ID matching works when a partner initiates this process:

  1. Identify user: A new visitor arrives on a web property that's tagged with the partner's media, ads, or data collection code.
  2. Send User ID: Partner's code loads the Audience Manager ID Sync URL, attaches the partner user ID, and makes a call to Audience Manager ID Sync URL.
  3. Synchronize IDs: Audience Manager receives the call and matches the user ID to an existing Audience Manager ID. If there's no corresponding Audience Manager ID, we'll create a new one and match it to the partner ID for that visitor.
  4. Return IDs: If required, Audience Manager can redirect to return the Audience Manager user ID to the partner

Audience Manager ID sync URL





Thanks Rachit. Do you know if there is a pre-requisite for the cookie to write to the browser and perform the sync? Would a user/device have to had visited a third party publisher site that is setup as an AAM destination? We can't seem to replicate this on our end, IP spoofing or anyting...

Hi Marc,


There are no pre-requisites for the demdex cookie to be set on the browser. 


The 3rd party Id sync happens because of settings done internally by Adobe audience manager per account.
Also the visitor does not need to visit the 3rd party's website to get this done.



You can reach out to Audience manager support team to troubleshoot your use case in case the Id sync's are not firing on your website.