Politicians do it. Businessmen do it. Secret societies do it. Even a well-trained dog does it. When it comes to handshakes, you've probably heard all the tired advice: Shake it like you mean it. Grip firmly, stand up straight, look them in the eyes.
But here's a more interesting question: Why exactly do we feel the compulsion to shake hands when we're saying hello, making a deal, or burying hatchets? Here's what the research says about this most common of rituals-and how the act can change the way people perceive us.
1. Why we shake it
As anybody who owns a rear-sniffing dog knows, animals use ritualised physical contact when they meet somebody new. Handshake-like interactions are likely ancient.
"At a basic level, you're literally showing your hand and letting it known that you can be trusted, because you don't have a concealed weapon or are hiding anything else," says Florin Dolcos, an assistant professor of psychology and neuroscience at the University of Illinois who has studied the science of handshakes.
"It's very primal, but this is how we probably started shaking hands in the first place."
Dolcos also points to a fundamental need for humans to connect physically with each other-especially when establishing a sense of trust and safety.
And while we're comfortable cuddling or hugging family members, a handshake allows for such touch in a way that is less likely to put strangers off-or weird them out.
Handshakes could also be used to, quite literally, sniff other people out. A 2015 study conducted at Israel's Weizmann Institute of Science used cameras to show that people often instinctively smell their hands after shaking somebody else's.
The researchers theorize that this behavior is similar to that displayed by other mammals, such as rodents and dogs, that often use their sense of smell as a part of social interactions.
2. It's about trust
In a 2012 study published in the Journal of Cognitive Neuroscience, Dolcos and his wife Sanda Dolcos, also a faculty member at the University of Illinois, found that simply adding a handshake to a social interaction made people more likely to view others more positively.
In the study, researchers placed subjects in an fMRI brain scanner while showing them movies of social interactions.
Some of these movies showed people engaged in "approach" behaviours that signaled a positive social interaction, while others included "avoidance" behaviors that suggested one person was less than thrilled to be interacting with the other.
With all types of interactions-friendly, unfriendly, and anything in between-adding a handshake caused test subjects to rate the people they viewed as more confident, trustworthy, and interesting.
"At a general level, it seems that shaking hands before a social interaction will make things more likely to go well," Sanda Dolcos says.
3. Touch can help seal deals-even bad ones
This study re-enforces another one published in 2010 in the journal Psychological Science that found that that minimal amounts of physical contact could increase a person's sense of security to the point that he or she is more likely to make risky financial decisions.
For the study, researchers at Columbia University and the University of Alberta greeted some test subjects with a 1-second pat on the back of the shoulder prior to giving them the option of choosing between a certain cash payout or a risky bet.
Those who received the touch were far more likely to take the riskier route.
But guys shouldn't view this as carte blanche to get too touchy-feely with with clients: While the effect was seen on both male and female test subjects, it was present only when the person doing the touching was a woman-a result that researchers theorise could be related to feelings of maternal security.
And while handshakes certainly did put test subjects at ease, a light touch on the back of the shoulder (right below the deltoid, if you're asking) proved far more effective in creating a sense of security and encouraging subjects to go for the gamble.
"Doctors do this all the time, sometimes also salespeople," says Jonathan Levav, one of the study's authors who is now an associate professor of marketing at the Stanford Graduate School of Business. "Certain kinds of touch can make people more comfortable-consciously or nonconsciously-and that can have an effect on the decisions that they make."
Bottom line: A handshake or light touch on the shoulder really could help seal the deal-especially if you're a woman.