Do you greet a stranger by kissing them on the cheek or giving them a firm handshake? In the largest study ever quantifying where people were comfortable being touched and by whom, 1,300 men and women were asked the same question. The results suggest that when greeting most people, you’re better off with a handshake.

The participants, from Finland, France, Italy, Russia, and the U.K., detailed where strangers, family members, friends, and romantic partners were allowed to touch them. Researchers from the University of Oxford and Finland’s Aalto University then combined the results to create a so-called “heat map.”

Proceedings of the National Academy of Sciences / Quartz

For almost everyone, the hands are OK. Unsurprisingly, no one wanted relatives of either gender to touch their genitals. And, regardless of nationality, researchers found that the closeness of the relationship correlated with the range of areas that can be touched. There were, however, some unexpected results.

Oxford University’s Robin Dunbar, who co-authored the study, said: “We were a bit surprised at how reluctant men were [to be touched] compared to women.” The heat map showed that men weren’t even comfortable with other male strangers touching the back of their heads—it was a “taboo zone.”

The study, published in the journal Proceedings of the National Academy of Sciences, highlighted the importance of touch in communicating positive emotions. Humans are quite similar to monkeys and apes in that respect, with touch being crucial in establishing and maintaining social bonds.