What is a cookie, and how do cookies work with retargeting?

With a grower voice speaking up against the use of cookies, cookies have been seen as something bad. But be honest, what exactly are cookies, and why have they become such a hot topic on privacy concerns?

What is a cookie?

A cookie is a small text file that a website stores on your device, usually in your web browser. Cookies help websites remember your past interactions, such as whether you’re logged in, what’s in your shopping basket, and your preferred browsing language.

By storing this kind of information, cookies make your browsing experience smoother, so you don’t need to log in every time you visit a site.

Types of Cookies: First-Party and Third-Party

1st-party cookies are set by the website you’re visiting, like ayudante.jp. These help the site remember your preferences and activity on their pages.

3rd-party cookies are set by other websites, such as advertisers or analytics companies (like bing.com and google.com). These track your browsing behaviour across different websites.

In simple terms, 1st-party cookies mostly help the site remember your preferences within the website, making your browsing experience smoother. In contrast, 3rd-party cookies are mainly used for audience retargeting.

How Do Cookies Relate to Audience Retargeting?

First, we need to understand that a cookie has a name and value. The cookie name is the name assigned by the developer to distinguish the cookie, while the cookie value is normally an ID for attribution. For example, instead of your name, it might show a hashed value like a123456. This allows marketing platforms to remember your assigned identity and what you’ve viewed and shown interest in, without knowing your real personal information.

And then, each time you visit a website, a cookie is placed on your device or browser. This cookie tracks your browsing activity and interests. The website can then use this data to identify you on other sites and show you ads related to what you previously looked at. For example, if you visited a hotel website, the cookie would allow that hotel to show you ads on other sites.

To see which company placed a cookie to retarget you, check your browser’s cookie settings. Look at the domain name of the cookie, and you’ll find the company or media platform responsible.

The Power of Third-Party Cookies in Audience Retargeting

Let me use a 3rd-party cookie (name: IDE) set by Google Campaign Manager (previously known as “DoubleClick”) as an example for demonstration:

On web page A, the cookie value is “AHWqTUnY_-InO31aZ4ZBi3pfWSHFgoUHI3ZQMg8E_rCt4HClO1x9xRtORyWpmr8Mabo”.

On the another web page, you would fine the cookie value still stay the same “AHWqTUnY_-InO31aZ4ZBi3pfWSHFgoUHI3ZQMg8E_rCt4HClO1x9xRtORyWpmr8Mabo”.

This means that the entity setting the cookie (doubleclick.net) understands your identity and interactions across different web pages. Consequently, they can build a database based on your interests and sell this audience data to ad sponsors.

Common Misconceptions About Cookies

  • Disallowing cookies doesn’t eliminate ads but changes how they are targeted.

Blocking cookies does not mean you will stop seeing ads; it only means the ads will be less personalised, similar to seeing irrelevant ads in a subway station.

  • Cookies are not likely to make your PII exposed

Cookies are just small text files stored on your device or browser. Many cookies, regardless of being first or third party, do not contain personally identifiable information (PII). It is essential to implement robust security measures to protect the storage and transmission of cookies, thereby preventing any exposure of PII.

  • Targeted advertising actually support free content creation

Targeted advertising supports the availability of free content on the internet, often sponsored by ad operators. However, measuring the Return on Ad Spend (ROAS) is becoming more challenging without precise attribution. This difficulty might lead ad operators to reduce their budgets for internet advertising, negatively impacting content creators.


I understand retargeting with 3rd-party cookies might make you uncomfortable. That’s why there are campaigns happening around the phasing out of 3rd-party cookies. In my next blog, I will discuss the background of 3rd-Party Cookie Deprecation (3PCD) and what digital marketers can do next.

Jasper Poon

Solution Consultant, Business Development

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I have solid expertise in digital project management, data collection (by GA), and visualisation. I firmly believe no single platform can tackle all modern challenges in the digital world. Alongside solid knowledge in GMP products, I am also passionate about Google Cloud and other UX analysis tools. In my free time, I find joy in cats, swimming, and football.