Let’s check what we’ve heard and what we think we know against the science.

It was in physical education class when Laila Gutierrez swapped out self-harm for a new vice. The freshman from Phoenix had long struggled with depression and would cut her arms to feel something.

Teenage smoking has declined sharply over the past 25 years, due mainly to successful anti-smoking policies and efforts, coupled with rising education levels and lower smoking rates among parents.