Why is it Necessary to Clear Cache and Cookies (Temporary Internet Files) from Browsers?


 Safari, Firefox, Internet Explorer or Chrome browsers


Unexpected or undesirable behavior from web browsers


To clear your browser cache and cookies, see "Clear Cache and Cookies (Temporary Internet Files) in Multiple Browers" in this knowledge base. To understand why this fixes problems, continue reading below.

What is a browser cache, and what does it do?

Most web pages (like http://umich.edu) aren't made up of just one file. Instead, pages include many separate elements - files, scripts, procedure calls. Each of these elements must be requested by the browser, and downloaded to your computer, so that the web page's content can be displayed. The browser usually stores each of these downloaded files in a “cache” on the workstation. On subsequent visits to the web page, the browser will attempt to load the “cached” file, rather than request a new copy from the web server. Caching speeds up your browser experience (it takes much less time to locate and load a file on your hard drive than to download that file from a server). It also reduces the amount of network traffic required for web browsing.

What is a browser cookie, and what does it do?

A browser cookie is a file created by the browser at the request of a web site being visited. This “cookie” file typically stores user- specific information for that web site, such as:

  • authentication data (such as Cosign and Shibboleth)
  • selections from web forms and shopping cart contents
  • buttons you've clicked
  • web pages you've visited (sometimes for months or years)

The contents of the cookie are frequently updated, and are uploaded to the web site you're visiting when they're requested.

How Do They Work Together?

Each browser application (Internet Explorer, Google Chrome, Mozilla Firefox, Apple Safari) maintains its own set of “cached” files and cookies. Each browser's cache may have many thousands of files. Each browser's cookie store may have scores of cookies. All of these files are updated/refreshed/expired constantly. It's the browser's job to choreograph all of these changes, without disturbing the user's day.

And usually it just works.

Why do they Fail?

There are numerous reasons why a browser's collection of cache and cookie files may cause problems. Among the top culprits (in no particular order):

  • The web page you're visiting may have been designed improperly.
  • You may have frequently visited or reloaded the same web page, and some of the web site's contents may have changed - but your browser hasn't figured out that these changes have been made. This frequently happens with MPathways systems, for example.
  • A temporary network glitch may have occurred just as a cookie was being updated or a file being downloaded/stored.
  • Plugins fail, or the content that's being used by the plugin fails. (Most everyone can remember a Flash video that fails to load or crashes the browser).
  • Cookies may have been written or updated improperly, or haven't expired properly.
  • Files that are cached may be incomplete.

For whatever reason, your browser becomes confused. It's no longer able to find the correct file to display, or the correct cookie information to pass back to the web site you're visiting. When this happens, we say that the cache, or the cookie store, is “corrupted”.

When web pages start misbehaving in your favorite browser, then the chances are that your technical support person will ask that you clear the browser's cookies and cache first, before any further troubleshooting is done. It's a pretty simple procedure; it's relatively quick and painless; and in about half of all browser weirdness calls, it's effective.

When should the cache/cookies be cleared?

  • When a web page won't complete loading
  • When a web page continually redirects to another - for example, “Redirecting…Please wait” message
  • A web page completes loading, but the page is incomplete or is missing information
  • Random browser error messages
  • After a planned maintenance of the workstation (or an unexpected system crash).

Additional Information

Need additional information or assistance? Contact the ITS Service Center.