Sociologists have long said people who form bonds are less likely to kill themselves, but sometimes the opposite is true—studies now show that one person’s suicidal behavior can spur another’s, and one death can lead to more deaths.

Decades of research prove that a startling range of emotions and behaviors can be contagious—from moodiness to yawning. Young people are especially susceptible; they obsess over fads and fashion trends and copy illicit behaviors from peers, such as smoking, drinking or speeding. Or suicide. Using a statistical formula typically applied to tracking outbreaks of diseases, researchers at Columbia University and other institutions confirmed in 1990 that suicide is contagious and can be transmitted between people. Contagion spreads either directly, by knowing a suicide victim, or indirectly, by learning of a suicide through word-of-mouth or the media. Those same researchers found that people ages 15 to 19 are two to four times more prone to suicide contagion than people in other age groups. The way it spreads can be so similar to that of diseases that the Centers for Disease Control and Prevention (CDC) has sometimes gone into a region to investigate spikes in suicides.

Analysts call those spikes suicide clusters—an unusually high number of people in an area kill themselves (or attempt to) in a short period of time. The clusters tend to happen where people socialize, such as schools, psychiatric hospitals or military units. Madelyn Gould, one of the analysts who made the contagion discovery, has said these clusters make up between 1 and 5 percent of teen suicides but are vitally important to understand because “they represent a class of suicides that may be particularly preventable.” And a few consecutive suicides can devastate a community.