The nofollow designation tells search engines that a link should not pass trust signals to the linked page.
What is nofollow?
The nofollow attribute ensures that either individual links or all of the links on a page should not be followed.
This means that no trust signals (PageRank) are passed on via these links. The links do not, therefore, do not have as much influence on search engine rankings.
What does nofollow do?
According to Google, the Googlebot does not follow nofollow links. This means that the target page cannot be found via nofollow links (keyword discoverability) and no PageRank signals are passed on via these links.
Why are URLs that are linked via nofollow still found and crawled?
It is often the case that URLs which are frequently linked via nofollow are still crawled and appear in Google’s index as a consequence.
According to Google, however, this is because these URLs are linked to from other websites that do not use the nofollow attribute – or because the website itself makes the URL known to Google through its sitemap.
How can I use Nofollow?
In general, there are three ways to mark links with nofollow, and there is one other way which should not be used.
Correct: nofollow as an attribute on a link
The rel=”nofollow” attribute can be added to a link to mark that individual link as untrustworthy.
<a href="http://www.jetzt-billige-backlinks-kaufen.com/" rel="nofollow">sehr spammig Spamseite</a>
Correct: nofollow as an attribute in the meta tag of the <head> of the page
The meta tag name=”robots” can be used to store instructions for all or only certain crawlers. In addition to the noindex instruction, a nofollow can also be defined here.
If a nofollow is used in the robots meta tag, then all links on the page are treated as nofollow links.
<meta name="robots" content="nofollow" >
Correct: Nofollow as an instruction in the HTTP header of the page
All of the links on a page can also be set to nofollow at the same time via the page’s HTTP header.
X-Robots tag: nofollow
Caution: Before you add nofollow for the entire page, either via meta robots or via HTTP header, please think carefully about why you really want to apply the nofollow attribute to all links, internal and external, on the page. It is quite easy to shoot yourself in the foot with these two instructions.
Incorrect: nofollow in the robots.txt file
Sometimes there are instructions in robots.txt files that have no business being there. Nofollow is one of them and should not be used in the robots.txt file.
Google provides extensive documentation on the robots.txt file.
Why does the nofollow attribute exist?
Google introduced nofollow in 2005 to stop comment spam. It was intended to give webmasters the opportunity to tell Google which links should not be trusted.
Areas of application for Nofollow
Generally, nofollow is used when you want to include a link from your own page to another page that you do not trust. It is also used in instances where the link has been bought/sold.
Google-compliant link purchase
In the Webmaster Guidelines, Google points out the following in the subsection on “Participation in link exchange programmes”:
Any links intended to influence a website’s PageRank or ranking in Google search results may be considered part of a link exchange programme and thus regarded as a violation of Google’s Webmaster Guidelines.
The nofollow attribute removes this possible influence from the equation and makes it possible, for example, to buy visitors from websites who fall into a target audience. In such instances, the purchased link must of course be marked accordingly and have the nofollow attribute.
Influencing the link history of one’s own page aka PageRank Sculpting
If Google does not follow a link and does not pass on any trust, then no PageRank is lost as a result. This was still the case in 2005, which led to the practice of PageRank Sculpting.
However, this changed in 2009, and PageRank Sculpting has been discouraged ever since.
Influence of nofollow links on rankings
Since nofollow links are not tracked by Google, they have no direct influence on rankings.
If lots of visitors come to a page via a nofollow link – this is very often the case with links from Wikipedia, for example, where all Wikipedia links are set to nofollow – and regard the page as helpful, it is quite possible that the link will have a branding effect, which may lead, in turn, to follow links from the site visitors.
Nofollow and the disavow file
Google offers a possibility to declare links invalid with the disavow file. Google itself explains that links to domains or URLs on the disavow file are treated more or less as if they were nofollow.
Thanks to the “more or less”, Google leaves itself room to technically evaluate these links in a different fashion; in practice, however, a webmaster can assume that these links behave as if they were nofollow.