Suicide has become the second-most common cause of death among teenagers and young adults, overtaking homicides and outpaced only by accidents.

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“Just looking at these numbers, it’s hard not to find them completely disturbing. It should be a call to action,” said Lisa M. Horowitz, a pediatric psychologist at the National Institute of Mental Health. “If you had kids suddenly dying at these rates from a new disease or infection, there would be a huge outcry. But most people don’t even know this is happening. It’s not recognized for the public health crisis it has become.”

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The report released Thursday by the Centers for Disease Control and Prevention also showed homicides among ages 10 to 24 increasing 23 percent from 2014 through 2017 after a long period of decline. This trend mirrors a similar uptick in homicides across other age groups, said CDC statistician Sally C. Curtin, who compiled the new report.

Firearms are one factor looming over both worrisome trends. The United States has more guns per capita than any other country. It also has by far a higher rate of gun deaths than any other wealthy country. And while violent homicides often grab headlines, more gun deaths every year are attributed to suicide.

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The sharp increase in teen suicides has especially frustrated and puzzled researchers, who have struggled to explain its causes. Some have attributed it to changing social structures, lack of community and the rise of social media and smartphones. Others have pointed to bullying and less sleep.

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“The truth is anyone who says they definitively know what is causing it doesn’t know what they’re talking about,” said Ursula Whiteside, a researcher with the University of Washington. “It’s a complex problem with no easy answers so far.”

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Many studies, for example, have explored the ways social media might exacerbate depression and stress in teenagers. But at the same time, other studies have shown social media to be a positive force — reaching isolated individuals and creating social connections that didn’t exist before.

The Internet may have made it easier to research lethal ways of killing oneself. But at the same time, it has made resources such as suicide prevention hotlines and text and chat programs more readily available than ever.

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“If you asked 10 years ago, no one would have known where to call when they’re in a crisis,” said Jill Harkavy-Friedman, vice president of research for the American Foundation for Suicide Prevention. “Now we have a number, 1-800-273-8255. There’s even a catchy song about it ,” referring to the Logic song of the same name.

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Suicide deaths among youths remain relatively uncommon compared with much larger numbers of deaths among those who are middle-aged and elderly. Still, the sharper increase among youths is alarming because of the trajectory it suggests.

“It points to how important early intervention is to the prevention effort,” said Harkavy-Friedman, pointing to numerous studies showing that early intervention — such as suicide screening at emergency rooms and pediatricians’ offices — can have a large effect on the number of suicide attempts.

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