Parents wonder if their children's constant use of Instagram, Facebook or Snapchat is healthy. Teenagers talk about the pressure to post the perfect photo or to compete with the perfect lives their friends present on the Internet.

Doctors are hearing more and more about the damage being caused by social media, said Pate. Almost any teen involved in social media has probably been harmed by it in some way, he said.

Researchers and scientists are still trying to figure out how social media use affects young people. So far, the evidence is mixed.

Studies have shown the around-the-clock world of social media takes a mental and emotional toll on some young people. It has been linked to increased worrying and feelings of depression.

Depression is more serious than sadness. It can feel like an inability to be happy. Depression is often caused by physical imbalances of chemicals in the brain. Sometimes, though, outside factors such as social media can affect mood and worsen depression.

Social media can also have a positive effect, however. For example, it can be a useful resource for teens. It can help them find social support when they are struggling with life issues, and it can provide them with a place where they can express themselves. Some teens are able to build real friendships with people they only know through social media.

However, one recent study cast social media in a decidedly bad light. It found that the more time teens spend on social media, the more likely they are to feel depressed and have problems sleeping.

Researchers have also found a link between social media use and poor body image, which can lead to eating disorders. A recent survey conducted by London's Royal Society for Public Health suggests that Instagram and Snapchat are the most likely to cause body-image problems among teens. Young women, in particular, are bombarded with images of perfect bodies. Many of those images are digitally edited to mask people's flaws and imperfections.

Teenagers are already self-conscious and easily affected by what others say, said Dr. Pate. They may start comparing their lives to those of people on social media. They may think comments people make on social media are directed at them when they are not. Or, they may misinterpret what someone says.

Many experts say social media can be dangerously addictive. Some doctors believe excessive social media use should be officially recognized as an addiction, like addiction to drugs or cigarettes.

The more loaded with images a social media site is, and the more rapidly content changes, "the greater the chance of an addiction," said Dr. Bankole Johnson. Teens who get hooked on such forms of social media find it hard to spend too much time away from them. Their schoolwork can suffer as a result. So can their personal relationships and their moods.

However, some experts warn against seeing social media as purely harmful. They point to studies that have found positive effects.

One study found that social media helps teenagers who play video games excessively. Heavy gamers who have a network of friends on social media seem to do better than those who play the games a lot and don't have similar social networks. They seem to be less likely to experience feelings of depression and worry, said researcher Michelle Colder Carras.

Carras said that care needs to be taken when making a direct link between mental health and social media use. She said it is not always clear whether social media is really the cause of the problem. 

The Royal Society survey that found a link between social media use and body-image problems didn't dig deeply enough, Carras said. It didn't ask whether the teens already had mental health problems. It also didn't try to determine if those problems could have been linked to something else.

The Royal Society lists several proposals for easing the ill effects of social media. Sites like Instagram could highlight when people have digitally edited their image or post warnings about the dangers of too much social media use, the group said. It also suggested that schools teach safe social-media use.

In severe cases, some teens might need to give up social media completely, Dr. Pate said.

Others might need to be restricted to socializing with a select group of people. Parents can also help by limiting the amount of time their children spend on social media.

"It boils down to what the kids can manage and handle when it comes to the stress created by these sites," Dr. Pate said. "We want the kids to individualize their own approach."