The new policy will give teens the choice of switching their settings so their posts can be accessible to the general public. That option already has been available to adults, including users who are 18 or 19.
As a protective measure, Facebook will warn minors opting to be more open that they are exposing themselves to a broader audience. The caution will repeat before every post, as long as the settings remain on "public."
The initial privacy settings of teens under 18 will automatically be set so posts are seen only by friends. That's more restrictive than the previous default setting that allowed teens to distribute their posts to friends of their friends in the network.
In a blog post, Facebook said it decided to revise its privacy rules to make its service more enjoyable for teens and to provide them with a more powerful megaphone when they believe they have an important point to make or a cause to support.
"Teens are among the savviest people using social media, and whether it comes to civic engagement, activism, or their thoughts on a new movie, they want to be heard," Facebook wrote.