Some years ago Google has implemented No-Follow backlinks to fight against massive comment spam. Since then many blogs are declaring the links built within their comment areas automatically/by default as No-Follow ones.
Now the question is which value No-Follow backlinks have and if a large number of them linking to your website will cause a negative impact on a website’s Search Engine Ranking?
First of all let’s have a look at the main difference between Do-Follow and No-Follow backlinks. A Do-Follow backlink means that the original site where the backlink is located inherits the link target a part of its PageRank and Trust. On the other hand a No-Follow backlink does not inherit the link target any values. But No-Follow backlinks are counted by Google as a value of seriousness, because only a mix of Do-Follow and No-Follow backlinks provides a natural link building ratio. Therefore even a large number of no-follow backlinks pointing to your site will not be evaluated by Google as bad signal (Statement from John Mueller, Google Webmaster Tools).
Surprisingly it’s recommended to website owners to build No-Follow backlinks beside Do-Follow ones. This will count as a proof that your website has a natural and serious link flow. In addition another advantage is that No-Follow backlinks bring traffic to your website not from the search engine but form the websites themselves (where the no-follow backlinks are located).
To conclude No-Follow backlinks have no negative impact on your rankings, even if there’s a large number of them pointing to your website.