A Google Webmaster video released today aims to answer the burning question surrounding porn sites’ lower PageRank.

The question asked of Google’s Matt Cutts was as follows:

What are the technical reasons porn sites have such low PageRank? None go over PR6. A lack of links from trusted sites? Rampant link exchanges with low quality sites? Penalties for affiliate links? Or is there a general penalty on the industry? Studio 3X, New York

Matt Cutts says that his best guess is that it has to do with popularity vs. links. Google doesn’t have some sort of anti-porn rule, its just that PageRank looks at the number of links and the quality of those links to a site, not really the popularity of the site.

He says, “People very rarely link to porn sites, even though a lot of people visit a lot of porn sites.” If PageRank equaled popularity, then porn sites’ PageRank would be right at the top.

Watch the whole webmaster video below: