Google invented a tag called "nofollow" to give webmasters better controll about how a site spreads its link power. In this article I'll describe in detail how this tag works and how you can benefit from it. It contains some secret information about how Google handles links and Nofollow.
In fact the "nofollow tag" is not a tag at all, but it's some times more simple and easier to understand if you call it a "tag". Actually there is an attribute called rel, which may be part of any anchor tag you place in your webpages. The W3C tells us: "The rel attribute specifies the relationship of the linked document with the current document."
The implementation looks like:
<a href="http://www.example.com" rel="nofollow">Example Link</a>
It's documented that Nofollow means the link will not be used as a reference for the target document. In terms of Google this means, the link will not transfer PageRank to the target document. Same is valid for all other mayor search engines, even if they don't call it PageRank. So in a more generic way SEOs talk about Link Juice: no link juice will reach the target document if you place a rel="nofollow" attribute in the link code.
At first glance this concept seems to be simple. But as soon as you think twice, a couple of questions arise. At least when optimizing your sites a bit more than usual, you'll stumble uppon the same questions as I did. As I found the answers and was able to enhance my SEO insider knowledge a bit further, I'd like to share the information with you.
The answer is, there is nothing special to it! Nofollow does the same good job for ballancing internal links, as it does for external links. You don't have to worry about getting a penalty of your mayor search engines. Even the Google quality team speaker Matt Cutts talked about this use of Nofollow. Typically you should mark the following kinds of links with nofollow:
The answer is, it depends! If there are other pages or sites linking to that page, it will still be indexed. It just doesn't receive "link juice" through the nofollow-link. It will therefore be likely less good ranked in the search engine result pages (SERPs). Nofollow is no appropriate way of removing pages from search engines. To remove pages, use robots.txt file or the robots meta-tag.
Link juice is very similar to PageRank. It's the juice running through the veins of the Internet and of your websites. The more link juice a page receives, the more important it is.
To stay in the above terminology, if Link Juice is the blood, links are the veins. Setting many links to a page means giving it much Link Juice and therefore making it more important.
Nofollow affects the flow of Link Juice. It devalues a link and stops the flow of Link Juice through it. By setting nofollow you can lower the importance of a page, depending on how many links you devalue.
Well, I did a research on how Google handles this. Other search providers might handle it similar or not. For Google, only the first link on a page counts. Lets consider there are two links to the same page, one with and one without Nofollow set. This is how these links are rated:
A last note about the second case above. Google actually only uses one link to a target per page. That means the second link isn't recogniced anyway, no matter if it's nofollow or not. It's always only the first link that counts. This is what even the most SEOs aren't aware of, so please keep it a secret ;)
Enough for now. You're kindly invited to drop a comment if you'd like to discuss this topic, and to shed some light on topics not yet covered.