Over the past few years, as the cold glow of a smartphone has followed more and more adolescents from bedroom to school and back again, parents have fretted over the technology's influence. With Facebook researchers studying how its apps erode girls' body image, doctors describing TikTok-induced tic disorders, and prosecutors and lawmakers promising to hold social media companies responsible for harming children, it's no wonder.

A quieter scientific discussion has questioned whether social media is doing much harm. Some researchers claim that digital technology is a factor in the rising rates of mental health problems, but others argue that the risk of harm for most teenagers is insignificant.

The authors of the paper published a large, multiyear study looking at the relationship between social media and adolescents' feelings about life.

Analyzing survey responses of more than 84,000 people of all ages in Britain, the researchers identified two distinct periods of adolescence when heavy use of social media spurred lower ratings of life satisfaction.

The study found that the relationship between social media and an adolescent's well-being was weak. It suggested that there were certain periods in development when teenagers may be most sensitive to technology.

Amy Orben, an experimental psychologist at Cambridge University, said that the links between social media and well-being might be different across different ages.

In the United States, screens are a big part of life for most adolescents. Nine out of 10 American teenagers have a mobile device, and they are spending a lot of time on it.

The rates of depression, anxiety and suicide among teenagers have gone up over the past two decades as social media use has gone up, leading scientists to wonder if these trends are related.

It has been suggested that social media may have an indirect effect on happiness by replacing other activities that are important for mental and physical health. Adolescent sleep patterns seem to be disturbed by heavy social-media use.

There is not much research looking for a direct relationship between social media and well-being.

There have been hundreds of these studies, almost all showing small effects.

The scope of the new study is noteworthy, said Dr. Hancock, who was not involved in the work. 84,000 people were surveyed in Britain. One of those surveys followed more than 17,000 adolescents over the course of a year, showing how their social media use and life satisfaction changed over time.

In terms of scale, it's fantastic. The rich age-based analysis is a major improvement over previous studies, which tended to lump all adolescents together.

Heavy use of social media during early adolescence predicted lower life-satisfaction ratings one year later. The sensitive period for girls and boys was between 11 and 13 years old. Dr. Orben said that girls tend to hit puberty earlier than boys.

Adolescent girls go through a lot of development earlier than boys, according to Dr. Orben.

The study found that both the boys and girls had a second period of social media sensitivity around the age of 19. She said that many people go through major social upheaval around that age, like starting college, working in a new job or living independently for the first time, that might change the way they interact with social media.

Although the new report drew from richer data sets than previous studies did, it lacked some information that would be helpful in interpreting the results. It's not ideal to wait a whole year between responses. Although the surveys asked how much time the participants spent communicating on social media, they did not ask how they used it; talking to strangers while simultaneously playing a video game might lead to different effects than texting with a group of friends from school.

The findings suggest that a small subset of teenagers could be harmed by social media, while most teenagers are not affected. Predicting the risks for an individual child is impossible.

What does that mean for your child? Michaeline Jensen is a clinical psychologist at the University of North Carolina at Greensboro. She said that most of the kids would not go from normal functioning to clinical levels of depression. It's not to say that none of them would.

The study found that people who felt bad about their lives spent more time on social media a year later. The technology may be a way for some people to cope with their gloom.

The experts said that they were often frustrated by the public debates about social media and children, which often inflate the platforms, harms and ignores the benefits.

It carries risks like peer influence and substance use.