Nofollow

Google introduced the `rel='nofollow'` attribute in 2005 to combat link spam in blog comments and forums^[1]. Before nofollow, spammers posted thousands of comments on blogs purely to get backlinks — each comment link passed PageRank to the spammer's site. By adding `rel='nofollow'`, webmasters could signal to Google that a link should not be followed for PageRank purposes. This effectively removed the incentive for comment spam. In 2019, Google expanded the system with two new link attributes: `rel='ugc'` for user-generated content (comments, forum posts) and `rel='sponsored'` for paid or affiliate links. All three are treated as hints rather than directives — Google may choose to follow them.

The three link attributes serve distinct purposes but all prevent (or reduce) PageRank transfer^[1][2]. `rel='nofollow'` is the general-purpose signal for any link you don't want to endorse. `rel='sponsored'` is required by Google's guidelines for paid links, affiliate links, and advertorial content — using 'nofollow' on paid links is acceptable but 'sponsored' is more specific. `rel='ugc'` is for user-generated content where you can't vouch for the destination. You can combine attributes: `rel='nofollow ugc'`. The practical difference between them for most sites is minimal — Google treats all three similarly in terms of link equity. The critical distinction is that paid links that pass PageRank without a nofollow or sponsored attribute violate Google's spam policies.

Use nofollow on: paid links and sponsorships, affiliate links, user-generated content you can't vet, login pages and thank-you pages you don't want crawled, and advertising. Do not use nofollow on internal links to your own pages — this was a popular tactic called 'PageRank sculpting' that Google has confirmed doesn't work as intended and can actually harm PageRank flow by creating crawl dead-ends^[2]. Also avoid nofollowing links to your most important pages. Nofollow links from high-authority sites (Wikipedia, major news sites) are still valuable for referral traffic even without passing PageRank — and Google has confirmed it uses nofollow links as hints that may influence crawling even if not full PageRank transfer.