Cookies and cache

By Martin Edwards

Published March 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. And when you log into a site, a cookie is often used to remember this so you don’t have to log in again next time.

Note: To protect your privacy, a cookie can only be retrieved by the website that put it there. For example, if you tell the BBC you’re in Oxford (to get a weather forecast) this can’t then be disclosed to other sites you visit. Despite this, cookies sometimes get a bad name because they can be used to build a picture of your interests to show you ‘targeted advertising’.


Something else that accumulates on your computer when you visit websites is a cache. This stores parts of pages so the computer 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 web 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

Now visit the website and try to do whatever it was that wasn’t working before.

If a seemingly-broken site works correctly in incognito mode, 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 actually solve the problem, so you can resume browsing as normal. This means clearing the cookies and cache.

Solution (clearing cookies and cache)

Note: Before you clear cookies and cache, be aware of this potential inconvenience: 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 have to enter your password again, even if you don’t normally.


  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 your cookies and cache occasionally does not indicate a fault with your computer and should not be something you 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.