There have been increasingly loud public warnings that social media is harming teenagers‘ mental health – most recently from the US surgeon general – adding to many parents’ fears about what all the time spent on phones is doing to their children’s brains.

Although many scientists share the concern, there is little research to prove that social media is harmful – or to indicate which sites, apps or features are problematic. There isn’t even a shared definition of what social media is. It leaves parents, policymakers and other adults in teenagers’ lives without clear guidance on what to be worried about.

“We have some evidence to guide us, but this is a scenario where we just need to know more,” said Jacqueline Nesi, a psychologist at Brown University, in Providence, Rhode Island, who studies the topic.

What counts as social media when it comes to teenagers’ health?

The surgeon general, Dr. Vivek Murthy, warned last month that social media carried a “profound risk of harm,” but he didn’t name any apps or websites. His report acknowledged that “there isn’t a single, widely accepted scholarly definition of social media.”

Most studies look at platforms with user-generated content, where people can interact. But that raises a lot of questions. Does it matter if teenagers see posts from people they know or don’t know? Does it make a difference if they post or just view? Do multiplayer games count? Dating apps? Group texts?

YouTube illustrates the challenge. It’s the most popular site among teenagers by far: 95% use it, and almost 20% say they do so “almost constantly,” Pew Research Center found. It has all the features of social media, yet it hasn’t been included in most studies. Some researchers speculated that YouTube may not have as many detrimental effects, because teenagers often consume it passively, like TV, and don’t post or comment as often as they do on other apps. Or, researchers said, it may carry the same risks – it offers endless scrolling and algorithmic recommendations, similar to TikTok. There is no clear data either way.

What don’t we know?

Reviews of the existing studies on social media use and adolescents’ mental health have found the bulk of them to be “weak,” “inconsistent,” “inconclusive” and “a bag of mixed findings,” and to be “weighed down by a lack of quality” and “conflicting evidence.”

Research has not yet shown which sites, apps or features of social media have which effects on mental health. “We don’t have enough evidence to tell parents to get rid of a particular app, or cut it off after a particular number of hours,” said Sophia Choukas-Bradley, a psychologist and director of the Teen and Young Adult Lab at the University of Pittsburgh.

It’s also hard to prove that social media causes poor mental health, versus being correlated with it. Most studies measure time spent on social media and mental health symptoms, and many, though not all, have found a correlation. But other researchers say measuring time spent isn’t enough: In these studies, it’s unclear if time on social media is the problem, or if it’s time away from other things such as exercising or sleeping. And the studies obscure, for instance, if someone is spending hours on screens to escape mental duress or to seek support from friends.

A few studies have tried novel approaches around these problems. One, early in Facebook’s rollout in the mid-2000s, compared college campuses that had received access to it with those that hadn’t, and found that its arrival had a negative effect on students’ mental health.

A carefully designed study – Project Awesome, at the University of Amsterdam and Erasmus University, in Rotterdam, Netherlands – looks at both the average effects of social media on 1,000 teenagers it surveys and how they differ by individual, and follows adolescents over time. It has found that time spent on social media is less of a factor than teenagers’ moods while using it.

Other studies have used brain scans to show that when adolescents looked at likes or frequently checked feeds, it activated brain sensitivity to social rewards and punishments.

What else does the research show?

“We most often find a small, negative correlation” between social media use and mental health, said Amy Orben, a psychologist who leads the Digital Mental Health Group at the University of Cambridge, in England. “But we don’t know what’s underlying that. It could be that those who feel worse start using more social media, it could be that social media makes them feel worse, or it could be socioeconomic status or something else causing that link.”

Overall, research finds that social media is not inherently beneficial or harmful, and its effects depend on individuals and what they see.

“We can’t say, ‘Don’t do X, Y is fine, stay away from Z,'” said Amanda Lenhart, head of research at Common Sense Media. “Unlike TV or movies, it’s impossible to know what children will see on social media ahead of time. Sometimes it’s hair dye or dance videos, but sometimes it’s white supremacy or eating-disorder content.”

Teenagers with certain vulnerabilities – such as those with low self-esteem, poor body image or social struggles – seem to be most at risk. One experiment found that exposure to manipulated images directly led to worse body image, particularly for girls more prone to compare themselves with others. Another found that using social media to compare oneself to others and seek approval was associated with depressive symptoms, especially for teens who struggle socially.

Social media often has positive and negative effects on the same person. Project Awesome found that its use is associated with higher levels of both depression or anxiety and happiness or well-being.

In a Common Sense report, teenage girls with symptoms of depression were more likely than girls without symptoms to say social media made other people’s lives seem better than theirs – and also more likely to say it enhanced their social connections. They found mental health resources on social media, as well as harmful suicide-related content. Overall, the largest share of girls said the effects of social media features were neutral.

Why isn’t there more solid research?

Academic research takes a long time – often years to get funding, develop studies, hire staff, recruit participants, analyze data and submit for publication. Recruiting minors is even harder. By the time a study is out, teenagers have often moved on to a different platform – much of the research about specific platforms, for example, is on Facebook, which most teens no longer use. Tech companies have also not shared enough data to help researchers understand their products’ impacts, the surgeon general’s report said.

How could future studies be more conclusive?

Experts said they would like to see research that examines specific types of social media content, and things such as how social media use in adolescence affects people in adulthood, what it does to neural pathways and how to protect youth against negative effects.

Jonathan Haidt and Jean Twenge, psychologists who have expressed great concern about social media’s effect on teenagers, have proposed an experiment in which entire middle schools are randomly assigned to avoid social media or not.

What should parents do in the meantime?

Experts agreed that waiting for research wasn’t an option. They also mostly agreed that some level of social media use was beneficial. “There are harmful negative developmental implications to not using social media at all, given this is where the social interaction happens,” Choukas-Bradley said.

Researchers said social media rules should depend on individual teenagers’ maturity and their challenges, and said addressing the risks should also be the responsibility of tech companies and policymakers, not just parents. They agreed on a few steps parents could take now:

– Set limits, especially around bedtime.

– Don’t give a young teenager a smartphone right away. Start with a smartwatch or a phone without internet.

– Talk to your teenagers. Have them show you what they’re seeing, ask them how it makes them feel, and discuss privacy and safety.

– Make a family screen-time plan that takes into account which activities increase stress versus provide long-term satisfaction.

– Model responsible internet use yourself.

It’s not about monitoring certain apps, said Caleb Carr, a professor of communication at Illinois State: “Instead, parents should engage with their kids. Just like parents did presocial media, talk about being good humans and citizens, talk about respect for others and themselves, and talk about how their day was.”