Boffins studying health campaigns aimed at keeping teens and others from drinking and driving, smoking and other risky actions have found that these will actually encourage bad behaviour.
The advertisers use shame and guilt to get their messages across but a study shows that it is a complete waste of cash.
Researcher Adam Duhachek, a marketing professor at Indiana University said that the ads do more harm than good, because they have the potential to spur more of the behaviour they're trying to prevent.
Duhachek and his colleague Nidhi Agrawal of Northwestern University showed that people acting badly already knew it was wrong and the ads were triggering a defensive mindset.
The mind switches to a defence which claims that bad things only happen to other people and allows them to underestimate how vulnerable they are to the consequences
Adverts that scare people aren't effective, but they cause a backlash where people actually drink more than if they hadn't been exposed to the ads, Agrawal said.
The study was based on several experiments involving more than 1,200 undergraduate students who looked at anti-drinking ads meant to elicit shame or guilt.
Duhachek's advice is that if people want to positively influence drinking, campaigns need to convey both the dire consequences and a message of empowerment.
He said that if you're going to communicate a frightening scenario, temper it with the idea that it's avoidable.