A study shows that self-harm and suicide attempts are climbing among teenage girls nationwide. Experts say it could be because of smartphones and increased time spent online. (iStock)

A 15-year study of emergency room visits reveals new signs of emotional suffering among the nation's young women and girls — particularly those in their middle-school years.

Emergency room visits for girls 10 to 14 who inflicted self-pain were relatively stable before 2008 but escalated in the years since, according to new data. It is unclear why the rate of self-injury among younger teens has climbed, though some experts say it could be because of the girls' access to smartphones and Internet bullying.

Self-harming behaviors like ingesting poisons, cutting and overdosing on drugs are strong indicators of suicide — the second-leading cause of death among people between 10 and 24 in 2015, according to data gathered by the Centers for Disease Control and Prevention’s National Center for Injury Prevention and Control, reported in a letter Tuesday by the Journal of the American Medical Association.

Suicide rates for both teenage boys and girls are on the rise. But the number of emergency room visits for boys ages 10 to 24 with nonfatal self-inflicted injuries has remained stable in recent years, while the number of visits for girls in that age group surged, according to the data.

Most girls and women were admitted to emergency rooms after ingesting pills or poisons, although some were treated for injuring themselves with sharp objects, according to the new data. From 2009 to 2015, the number of girls 10 to 24 admitted to emergency rooms for nonfatal self-inflicted injuries grew by 8.4 percent annually.

The data examined first-time visits for nonfatal injuries treated in 66 hospital emergency rooms nationwide from 2001 to 2015. About 29,000 girls and 14,000 boys with self-inflicted injuries were treated during those years, according to the Associated Press. While all the injuries were intentional, not all were suicide attempts, experts said.

The data is in line with rates of teen suicide, particularly for girls, whose suicide rate hit a 40-year high in 2015, according to the CDC. Over the past decade, suicide rates doubled among teen girls and jumped by more than 30 percent among teen boys.

From 2001 to 2005, girls between 10 and 14 rarely needed emergency room care for self-harm. About 110 girls per 100,000 visited hospitals for self-inflicted injuries during that time. After 2009, their rates of emergency room visits for those injuries began to match the rates of women between 20 and 24 — almost 318 per 100,0000 women, according to the AP.

The highest rate of emergency room visits for self-inflicted injuries was among older teen girls, who had about 633 visits per 100,000 in 2015. That rate was less steep after 2008, according to the AP.

Some researches say the rise in self-harm and suicide among teenagers could be because those born after 1995 are more prone to mental-health issues than millennials. The most likely reason for this, they say, is the rise of the smartphone.

Other researchers say financial pressures from the recent recession could be a factor, but Jean Twenge, a psychology professor at San Diego State University, dismissed that. Because the years between 2010 and 2015 were a period of steady economic growth, it's unlikely the economy or income inequality is a contributor, Twenge wrote in The Washington Post this week. The time teens spend on homework also did not significantly change between 2010 and 2015, making academic stress an unlikely cause of depression.

Instead, Twenge points to smartphones, which crossed the 50 percent threshold of ownership in late 2012, around the same time when teen depression and suicide began to rise. By 2015, 73 percent of teens had smartphones, according to the Pew Research Center.

In her research, Twenge found that teens who spend five or more hours a day online were 71 percent more likely to have a least one suicide risk factor, such as depression or making a suicide plan, than teens who spent only one hour a day online. Suicide risks overall increased after two or more hours a day of time online, she wrote.

Teens in every generation have experienced mental-health problems, Twenge said. Genetic predisposition, family environments, bullying and trauma are all common factors.

“But some vulnerable teens who would otherwise not have had mental-health issues may have slipped into depression because of too much screen time, not enough face-to-face social interaction, inadequate sleep or a combination of all three,” she wrote.

Read more: 

Mapping out the causes of suicide in teenagers and children

More charges filed against woman in Missouri teen’s suicide

We can sometimes get carried away with our phones and other technology. Here are some experts tips to help live intelligently with technology, without it consuming your life. (Jhaan Elker/The Washington Post)