Cookies and cache

By Martin Edwards

Last updated June 2018


Websites can place cookies on your computer. A cookie is a piece of text that the site can use to remember things you’ve done, like the items you’ve put in your shopping cart. When you log into a site, a cookie may be used to remember this so you don’t have to log in again next time.

To protect your privacy, a cookie can only be retrieved by the site that made it. For example, if you tell BBC Weather your location, this can’t then be disclosed to other sites you visit.

Cookies sometimes get a bad name because they can be used to build a picture of your interests to show you targeted advertising. But they cannot harm your computer.


Something else that accumulates on your computer when you visit websites is a cache. It stores parts of pages so the browser doesn’t have to repeatedly download them. For example, every article on Wikipedia includes the Wikipedia logo. After you look at one article, the logo is cached and doesn’t need downloading again when you look at other articles. This makes browsing faster.

Problems and diagnosis

Occasionally, a website may stop working properly because of a problem with its cookies or cached parts. For example, you might not be able to log in, you might see an error, or a page might just look wrong. When this happens, it’s worth trying the site in ‘private’ or ‘incognito’ mode, which temporarily isolates it from its cookies and cache:


  1. Click the menu (three dots, top right)
  2. Click New Incognito Window


  1. Click the File menu
  2. Click New Private Window

Visit the website again in this new window and try whatever wasn’t working before. If it now works, chances are it’s a cookie or cache problem.

Incognito mode is a great way to diagnose and bypass the problem, but most likely you’ll want to solve the problem, so you can resume browsing as normal. This means clearing the cookies and cache.


Note: You’ll be logged out of any accounts you use, like Amazon or Gmail. In other words, next time you visit those sites you’ll need your password.


  1. Click the menu (three dots, top-right)
  2. Choose More Tools > Clear Browsing Data
  3. Set the time range to All time
  4. Make sure Cookies and other site data and Cached images and files are ticked
  5. Click Clear Data


  1. Click the Safari menu
  2. Click Clear History
  3. Set the time range to all history
  4. Click Clear History

Having to clear cookies and cache occasionally does not indicate a fault with your computer and is not something you should worry about.

Need help?

I’m a computer technician and tutor serving North Oxford, Kidlington, Woodstock and the surrounding villages. Visit my home page to find out more and get in touch.