Depression among teenagers rose sharply over the past decade, especially among girls. At the same time, treatment for this condition has held steady, leading to what researchers say is a “growing number of untreated adolescents.”

In a study published in the December issue of Pediatrics, researchers found that in 2014, 11.3 percent of teenagers reported having a major depressive episode during the past year — an increase from 8.7 percent in 2005.

Teenage girls were particularly affected, with rates of past-year major depression increasing from 13.1 percent in 2004 to 17.3 percent in 2014. Depression among boys rose from 4.5 percent to 5.7 percent during that time.

These differences between boys and girls did not continue into young adulthood. But depression among young adults also increased — from 8.8 percent in 2005 to 9.6 percent in 2014 — mainly among 18- to 20-year-olds.

Researchers found no significant change in how many young people sought or underwent mental health treatment from their pediatrician or other primary care provider. These rates hovered around 10 percent.

Researchers used data from 2005 to 2014 from the National Surveys on Drug Use and Health (NSDUH) — which included survey responses from over 175,000 teenagers ages 12 to 17, and over 180,000 young adults ages 18 to 25.

Read more: Symptoms of teenage depression »

Girls at risk of depression

Untreated depression among youth is of particular concern because it is a risk factor for suicide.

According to the Centers for Disease Control and Prevention (CDC), in 2014 suicide was the second leading cause of death for 10- to 14-year-olds and 15- to 19-year-olds.

Previous studies have also found larger increases in depressive symptoms among girls than for boys in recent years. This coincides with a large increase in suicide among girls and young women since 1999.

The researchers suggest several possible reasons that girls are more affected — including a greater increase in cyberbullying or a possible link between excessive mobile phone use and depression.

Some mental health experts say that it may also have to do with negative messages that girls get from the media, family, friends, or society — such as that it’s bad to look or act a certain way, or that girls are not as smart as boys, or that their voices don’t matter.

“I see a lot of girls struggling because of this kind of internalized belief that they’re wrong in some way,” Eloise Erasmus, Ph.D., a licensed psychologist in Eagan, Minnesota, told Healthline. “I think that belief gets reinforced by how people interact and treat girls in this culture.”

Erasmus says that even when girls seek out help or try to speak out, they may be dismissed or patronized as being “emotional” or “too sensitive.”

This can further silence their already-marginalized voices.

“Girls start to internalize the belief that they’re not good enough, and then they don’t express their feelings,” said Erasmus. And their emotions sometimes come out as depression, cutting behavior, eating disorders, addiction, or other mental illnesses.

Teenage depression quiz »

Tackling youth depression

Earlier this year the American Academy of Pediatrics updated its 2007 guidelines to recommend that pediatricians routinely screen youth aged 11 to 21 for depression.

Before this change, 60 percent of pediatricians had already reported screening for depression. This same study, though, found that in 2013 only one-quarter of pediatricians treated or managed depression among their patients.

Even if pediatricians notice the symptoms of depression, though, young people may only infrequently visit a doctor. Which is why other ways of identifying depression are needed.

“For school-aged kids, a school-based program is going to be one of the most effective approaches, because they’re around school adults more than anyone else, other than maybe their parents,” Cricket Meehan, Ph.D., director of the Center for School-Based Mental Health Programs at Miami University, told Healthline.

One program that is helping school adults keep an eye on children is Youth Mental Health First Aid, funded in part by the Substance Abuse and Mental Health Services Administration (SAMHSA)

This training is targeted at adults who do not already have a mental health background — such as teachers, administrative staff, cafeteria staff, and bus drivers.

“All of those adults are learning to identify the signs and symptoms of mental health issues in young people,” said Meehan.

This includes learning to recognize what depression looks like in elementary, middle school, and high school kids.

But the training doesn’t stop there.

Adults learn how to get students into mental health treatment — whether that means visiting a school counselor or psychologist, or a community-based therapist or psychiatrist.

They are also trained to help kids come up with their own coping strategies — things they can do to reduce their symptoms, like reading or exercising or dancing.

“They’re able to have that conversation,” said Meehan, “and help encourage a student or young person to engage in those coping strategies.”

This may also help young people deal with negative messages in the media, like those that surfaced during the recent election — when many groups felt personally attacked.

Erasmus, though, says a broader shift is needed to stop the abuse and trauma that is feeding the cycle of depression.

“Until we, as a society, start evaluating and honoring human beings as they are — and who they are — depression is going to be prevalent in our society,” said Erasmus

Read more: What is suicidal behavior? »