But the new coronavirus compelled a handshake rethink. It's an exchange of potentially infectious microorganisms, no matter how amiable.
"Hands are like a busy intersection, constantly connecting our microbiome with other people's microbiomes, places, and things," wrote a group of scientists in the Journal of Dermatological Science. Hands are the "critical vector" for transmitting micro-organisms including viruses, they said.
But if that is no longer automatically acceptable, what will replace the handshake as a fixture of the social etiquette post-coronavirus? An elbow bump or a fist bump? Perhaps a traditional Japanese bow, or doff hat? How about Star Trek's Vulcan Greeting from Spock?
We are welfare beings. When we meet each other, we are pressing on flesh. We take our biggest organ, skin and mash it with somebody else's-naked. It has become clear just how intimate such a gesture is in the middle of the coronavirus. The human hand is fecund. We have hundreds of bacterial and viral species on our palms.
"Think about it," says Charles Gerba, a University of Arizona microbiologist and public health researcher who also answers to Dr Germ. "You may be picking up to 50 percent of the organisms on that surface every time you touch a surface." Our hands can carry Salmonella, E. Coli, norovirus, and respiratory infections such as adenovirus and mouth-to-hand disease. And, given how often scientists come across poops on our fingers and palms, our hygiene habits are far less fastidious than we think.
With the naked eye, we can see none of that.
And so we rely on scientists with agar plates to make the arching, spiraling, exploding patterns of bacterial effervescence visible, showing just what our mixture of fingers risks, something so simple as a handshake made in terrifying technical color.
Scientists may show us viruses, too. In animal cells, these must be studied, in a mosaic of tiny semi-circles that scientists often stain purple or red.
The cells are lovely, Gerba says, "and then they become colorless when they die." Gerba studies the movement of viruses. He will put a virus on the doorknob of an office or in the room of a hotel or somebody's home.
He says it only takes four hours for a virus to reach half the hands and half the surfaces in an office building, or about 90 percent of the surfaces in someone's home, on an office doorknob. A virus often moves from room to room in a hotel and sometimes to conferences nearby.
Gerba says he stopped shaking hands himself in 2003, during the first SARS outbreak. "I always tell you I'm cold," he says. "I don't have to shake their hand that way." Dr Anthony Fauci, the top U.S. infectious disease expert, sees it the same way since the pandemic hit.
"You never shake hands with anyone," Fauci said this month. "That is obvious."
Handshakes have been a way for humans to signal each other for a long time, and part of the ritual of seeking common ground.
"The handshake at the time of any agreement is what gets photographed," says Dorothy Noyes, a professor of folklore at Ohio State University.
U.S. long, tough squeeze President Donald Trump and French President Emmanuel Macron were a classic display of two men looking for dominance in 2018. Some handshakes, like Chinese President Xi Jinping's bouncing clasp and Japanese Premier Shinzo Abe's, take months to negotiate.
Handshakes are an awkward or smooth habit to break, even if we wish.
Minutes after announcing a ban on shaking hands to combat COVID-19, Dutch Prime Minister Mark Rutte enthusiastically pumped Jaap Van Dissel, head of the Dutch Infectious Disease Control Centre.
"Sorry, excuse me! No, that's unacceptable! Let's do it again,' said Rutte, breaking into a laugh.