In families where love and support are generally scarce, even perceived favouritism may lead to use of alcohol, cigarettes or drugs by children, says a study.
For families that are not very close to each other or disengaged families, favouritism was strongly associated with alcohol, cigarette and drug use by the less favoured children, the findings showed.
"With favouritism in disengaged families, it was not just that they were more likely to use substances, it also escalated," said professor Alex Jensen from the Brigham Young University in the US.
"If they were already smoking then they were more likely to drink also. Or if they were smoking and drinking, they were more likely to also use drugs," Jensen added.
The study involved 282 families with teenage siblings.
In these disengaged families, children who view themselves as slightly less favoured were almost twice as likely to use alcohol, cigarettes or drugs.
If the preferential treatment was perceived to be dramatic, the less favoured child was 3.5 times more likely to use any of these substances.
"It is not just how you treat them differently, but how your kids perceive it," Jensen said.
"Even in the case where the parents treated them differently, those actual differences were not linked to substance use - it was the perception," he explained.
So to prevent such perceptions from creeping in the minds of the kids, parents should show their love to a greater extent, the researchers suggested.
"As simple as it sounds, more warmth and less conflict is probably the best answer," Jensen noted.
The study appeared in the Journal of Family Psychology.