Oscar Gutiérrez/CNET

Whether they want to or not, nearly half of Tumblr's users are seeing porn on their dashboards.

Tumblr has had a hard time keeping porn off its site. In 2012, Tumblr founder David Carp said 2 to 4 percent of the site's traffic was porn-related. An Italian study published last month suggests that number has grown significantly.

Adult content has become so pervasive that more than one in four people on the site will end up seeing porn without even looking for it, according to the study. Tumblr didn't respond to requests for comment.

Only 0.1 percent of accounts on the Yahoo-owned social network are producing porn content, but 22 percent of the site's users follow, like or reblog content from those accounts. Because of those shares, another 28.5 percent of people on Tumblr are unintentionally exposed to porn, according to the study.

Men and women under 25 on Tumblr are following porn at about the same rate, according to the study, but as users get older a gap appears. More men are sticking with the social network for adult content, with the gap peaking among users between 40 to 55.

The researchers took a look at 130 million Tumblr users and 7 billion links posted on the social network. Tumblr has 329.6 million blogs and 144 billion posts.

Tumblr's community guidelines asks its users not to upload any sexually explicit video. "We're not in the business of hosting adult-oriented videos (and it's fucking expensive,)" reads its user policy.

It's also asked users who do post pornographic content to mark it as NSFW so users don't accidentally see adult content while scrolling through their dashboard.