If you're adding a link in the content of your page and you don't want to lose any link juice then you should use the nofollow link attribute. For example, you may want your article to be authoratitive on a particular subject but have a link in your page to another site. You can add a nofollow to the link and your page will retain its authority.

What you are in fact saying is that you do not editorially vouch for the quality of the linked-to page.This enables you as a content creator to link to a web page without passing on any of the normal search engine benefits that typically accompany a link (things such as trust, anchor text, etc.).

Background to the nofollow link

With the introduction of the nofollow link attribute, the big search engines united in the fight against comment spam. The idea of the nofollow link attribute is to disallow the passing of link juice from the blog or forum site to the destination URLs found in the web user comments. By placing the nofollow link attribute with all of the link tags found in the comments, you are simply telling search engines that you cannot vouch with confidence as to the value, accuracy, and quality of the outbound link. The intent was to discourage SEO black hats from utilizing comment spam.

The nofollow attribute was introduced in 2005 by Google, Microsoft and Yahoo to discourage comment spammers from adding their links. Comment spam is when people post comments on blogs or forums to promote their own sites.

The basic idea is that links marked with the nofollow attribute will not pass any link juice to spammer sites. The format of these links is as follows:

<a href="http://www.sitewithspam.com/" rel="nofollow">link text</a>

In the above example, the hypothetical website http://www.sitewithspam.com would not receive any link juice from the referring page.

What happens when Google sees the nofollow link?

When Google sees the attribute (rel=“nofollow”) on hyperlinks, those links won’t get any credit when they rank websites in their search results. This isn’t a negative vote for the site where the comment was posted; it’s just a way to make sure that spammers get no benefit from abusing public areas like blog comments, trackbacks, and referrer lists.

Which sites use nofollow?

You'll find that most publishers now use the nofollow tag to stop spammers taking advantage of their sites. This includes Twitter, Wikipedia, BBC, Wordpress and nearly all social networking sites. Many directory sites use nofollow links too so if you're thinking of paying for a link to your site from a directory site then you'll need to check that its a "follow" link otherwise you're wasting your money.

Further points on nofollow links

  • You should use the nofollow attribute sparingly, and only in cases where it really makes sense.
  • The specific link with the NoFollow attribute is disabled from passing link juice.
  • No other aspects of how the search engines deal with the page have been altered.
  • Note that although you can use NoFollow to restrict the passing of link value between web pages, the search engines may still crawl through those links (despite the lack of semantic logic) and crawl the pages they link to.
  • NoFollow does not expressly forbid indexing or spidering, so if you link to your own pages with it, intending to keep those pages from being indexed or ranked, others may find them and link to them, and your original goal will be thwarted.