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My friend Mario from Heerlen in the Netherlands asked me this question:
I know that the meta tag “nofollow” tells a search robot not to follow a link and prevents outgoing link juice to other sites. I also know that the tag “index” means that a page must be indexed by the robot. What’s a little confusing are the different combinations and the fact that you can seemingly use them separately for posts, comments and/or pages. There must be a way to explain these combinations in plain English so that it is once and for all understandable for everyone. Here they are:
index, follow
noindex, follow
index, nofollow
noindex, nofollow
What are the different consequences?
This is an excellent question, and I myself find it difficult to wade through all the documentation on the web that explains the uses of these different tags and their combinations. In my research I have found some very useful concrete examples that have given me some insight into the matter. I will try to lay it all out in English as plain as I can manage. 
The situation is more complex than I first thought, because there are other tags to consider besides follow and index.
Google invented the nofollow tag as a measure to contain link spam. When this tag is used by itself, it tells the Googlebot that the link in question will not change the page rank of the website the link leads to. If the nofollow tag is used alone, the search engine will still physically follow the link, in order to index the website it leads to, but the link will not raise the rank of the site. A link spammer is someone who adds comments indiscriminately to all sorts of sites in order to induce search engines to count the links leading back to his websites and therefore raise his rankings (which in layman’s terms means that when someone is searching for sites similar to theirs, theirs comes up higher on the page of the search results). If you know the links are useless for raising your rank, there is little point in spamming.
So, let us try to look at the consequences of each combination of tags and try to look at some practical examples.
First, here is what these tags look like, and where to put them. They must be located in the <head> portion of the html code of the page in question.
Index, Follow
<meta name=”robots” content=”index, follow”>
This is the default setting, so you never see this tag. In other words, if you do nothing, the Googlebot will index the page and follow the links it contains to go and index the pages they lead to.
Noindex, Follow
<meta name=”robots” content=”noindex, follow”>
An excellent example of when to use this meta tag is for a contact form page. There are many pages in the site that link to this page, but the page does not have valuable content. It is a useful page for readers of the site but only as a contact form, not for the purpose of reading and absorbing interesting information. But because many pages in the site link to this page, it has a lot of “link juice” and looks like it should rank highly. Therefore we can decide to NOT index this page, but to still allow the Googlebot to follow the outgoing links from this page to other pages.
Index, Nofollow
<meta name=”robots” content=”index, nofollow”>
A perfect example of when to use this meta tag is when the pages that the current page links to have time-sensitive content. I found one article in a Google blog that used a very good example. Let’s say that the page in which this tag appears talks about celebrities. In this page there are links to stories that are “breaking news.” After a few hours the breaking news is replaced by new breaking news, and the “old” breaking news stories are put into a longer lasting articles section of the site. With the “index, nofollow” tag we obtain the perfect result. The celebrities page is indexed and the Googlebot does NOT follow the links to the breaking news which will soon be replaced.
Noindex, Nofollow
<meta name=”robots” content”noindex, nofollow”>
Another reason not to index or follow certain pages and links is when there is duplicative content in a site, which is something that at times is unavoidable. If possible it is always best to keep the indexing and ranking of our sites as clean as possible and to try to avoid duplication of content showing up with separate rankings. So, if there are pages that duplicate the content of other pages, with links to yet other duplicative pages, we can use “noindex, nofollow” and avoid adding unnecessarily to their ranking. Other examples I found for “noindex, no follow” are “About” pages, which often have artificially high rankings because many other pages link to them, and “login” pages, which also get a lot of “link juice.”
I hope this answers your question, Mario! And if you would like to add anything, clarify, or add something to your question, feel free to do so in the comments!
See you next time!
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{ 3 comments… read them below or add one }
This is a great explanation. I will use this as a guideline whenever I doubt how to use these tags. Just have to warn you, because I will ask you more question that force you to do research. Keep up the good work Ilaria!
You’re very welcome, my dear.
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