Worried that your kid is a bit too shy? Well it seems that the answer may lie in how stressed out you are, and also in your genes.

A new study from the Child Development Laboratory at the University of Maryland shows that shyness in kids could relate to the manner in which a stress-related gene in children interacts with being raised by stressed-out parents.

The study was conducted by a team of researchers led by Nathan Fox, professor and director of the Child Development Laboratory, who found that kids who are consistently shy while growing up are particularly likely to be raised by stressed-out parents, and to possess a genetic variant associated with stress sensitivity.

This suggests that shyness relates to interactions between genes and the environment, as opposed to either genes or the environment acting alone.

"Moms who report being stressed are likely to act differently toward their child than moms who report little stress," said Fox.

"A mom under stress transfers that stress to the child. However, each child reacts to that stress somewhat differently. Our study found that genes play a role in this variability, such that those children who have a stress-sensitive variant of a serotonin-related gene are particularly likely to appear shy while growing up when they also are raised by mothers with high levels of stress," he said.

Like all genes, the particular serotonin-related gene examined in this study has 2 alleles, which can be long or short. The protein produced by the short form of the gene is known to predispose towards some forms of stress sensitivity.

Fox's research found that among children exposed to a mother's stress, it was only those who also inherited the short forms of the gene who showed consistently shy behaviour.

"If you have two short alleles of this serotonin gene, but your mom is not stressed, you will be no more shy than your peers as a school age child," said Fox.

"But we found that when stress enters the picture, the gene starts to show a strong relationship to the child's behavior. If you are raised in a stressful environment, and you inherit the short form of the gene, there is a higher likelihood that you will be fearful, anxious or depressed," he said.