When it comes to kicking a negative habit, stressful events are bad news.

It’s common sense that people often cling or return to their vices when life gets a little out of control; the draw of alcohol, tobacco, gambling or your third bowl of ice cream are strong when you’re feeling overwhelmed or down in the dumps. And many Americans may have similar triggers: a particularly rough patch at work or home, financial distress, terrorism.

Wait … terrorism? That’s right. Researchers from Cornell University found that after the September 11th attacks, significant numbers of Americans returned to smoking. And no, they weren’t all New Yorkers, or even New Englanders.

The scientists used information collected by health departments in every state, which was then analyzed in a national report. They found that many people across the country took up smoking again in the grief and anxiety caused by that dark day. The rate of ex-smokers returning to the habit was greater after the attack than it was before.

The data also showed that more people reported feeling stressed out. This effect was extra strong in communities with lots of military personnel or highly educated residents. The study authors say increased stress nationwide directly caused the revival in smoking.

The increase in revamped smoking habits carried on for at least two years, at which point the researchers stopped analyzing the data. Overall, enough people returned to smoking during this time to raise the rate of adult smokers nationwide by 2.3 percent.

The study also looked at smoking following the 1995 bombing in Oklahoma City, but didn’t find the same pattern. It’s not clear why.

But the researchers say major anxiety-inducing events in the future may warrant a new type of response: anti-smoking campaigns.