It's easy to be offended when a colleague yawns while you're talking. But that yawn may not mean what you think.

A growing number of researchers believe the purpose of this little-understood behavior is to cool the brain, says a researchreview published earlier this year in Frontiers in Neuroscience.

Changes in climateaffect how often people yawn. Researchers in an earlier study conducted outdoor interviews with two groups of people in Tucson, Ariz., one in early summer and one in the winter. People were asked to look at pictures of people yawning and talk about their own yawning behavior.

People were nearly twice as likely to yawn when they were surveyed during the winter, when they could inhale cool air to reduce the temperature of the brain, says the study, published in 2011 in Frontiers in Evolutionary Neuroscience. Participants yawned less when surveyed in the early summer, when temperatures outdoors were about the same as the human body.

Other studies show yawning increases after people experience heat stress or have a heat pack placed on their foreheads.

Yawning also may build empathy within groups. Yawns are seen as contagious, but 'catching' a yawn depends on a person's ability to feel empathy and closeness with the yawner, says a 2013 researchreview in the International Journal of Applied Basic Medical Research.

People observed in workplaces or restaurants yawned more often in response to others' yawns when they were kin or close friends with the yawner, the study says. People are less likely to engage in contagious yawns when they have emotional or social disorders that prevent them from feeling empathy, the study says.

What yawns don't accomplish, researchers say, is to re-energize the brain.