If you think there's no harm in a little white lie every now and again, you're wrong - new research says telling little lies can quickly snowball into bigger deception.
When people repeatedly lie, their brain adjusts, desensitising to the dishonesty. The effect is even stronger when the liar personally gains something from the mistruth.
The research, led by Londoners Neil Garrett and Tali Sharot, was published in journal Nature Neuroscience on Tuesday.
"The results show the possible dangers of regular engagement in small acts of dishonesty, perils that are frequently observed in domains ranging from business to politics and law enforcement," they wrote.
"Despite being small at the outset, engagement in dishonest acts may trigger a process that leads to larger acts of dishonesty further down the line."
The researchers used a scenario with a jar of pennies to test how lying affected the brain.
Several experiments were carried out where a person had to tell another how many pennies were in the jar. Sometimes dishonesty would benefit them both, sometimes just the liar, other times just the person being lied to, or benefiting one party but having a neutral effect on the other.
They found those who lied did so more frequently if it was self-serving.
"Escalation was significantly greater when dishonesty was self-serving than self-harming."
Brain scans showed emotional response progressively diminished to lies that were self-serving, but not self-harming.
The researchers said this could translate to escalations in risk-taking or violent behaviour.
"Our results highlight the importance of considering the temporal evolution of both behaviour and brain response in studies that involve repeated decisions."