Instagram's boss faces a grilling Wednesday from US lawmakers after damning press reports based on leaked internal research showed the photo-sharing app could harm its young users.

Adam Mosseri's testimony comes as the social media networks under Facebook parent Meta battle a crisis sparked by the company's own documents, and which have rekindled a years-old US push for regulation.

The documents leaked to reporters, lawmakers and regulators by Facebook whistleblower Frances Haugen include research from 2019 that found Instagram makes body image issues worse for one in three teenage girls. 

Another report, from 2020, revealed that 32 percent of teenage girls said that when they felt bad about their bodies, Instagram made it worse.

Facebook has pushed back fiercely against a string of Wall Street Journal reports based on the findings, and a subsequent series for a US media consortium, arguing its research was mischaracterized.

Senators Richard Blumenthal and Marsha Blackburn are leading the hearing, the latest in a series probing how social media could be making teens feel worse about themselves.

"My conversations with parents have deeply moved me to fight for... reforms and demand answers that the whole nation is seeking," Blumenthal said Tuesday.

Facebook has bounced back from other scandals like the one involving Cambridge Analytica, a British consulting firm that used the personal data of millions of Facebook users to target political ads.

In that case, CEO Mark Zuckerberg went to Washington to apologize and the company agreed to a $5 billion settlement with US regulators.

However, the leading social media network faces at least one investigation spurred by the latest crisis: a consortium of US states announced in November a probe of Meta's techniques for enticing young users and the potential resulting harms.

On the eve of Wednesday's hearing before a Senate commerce subcommittee, Instagram announced new protections for young users like suggesting a break if they have been spending a lot of time on the platform.

The timing of the announcement drew a wary reception from lawmakers, who questioned whether it was an effort at distraction ahead of the hearing.

Stephen Balkam, founder and CEO of advocacy group Family Online Safety Institute, said pre-hearing announcements are a Washington tradition but noted they won't make the app's problems go away.

"Instagram is safer than it was. I think Instagram is less toxic for teens than it was. But it will never be perfect, it will never be fully safe. But then that's true of all social media," he told AFP.