BRUSSELS — Manon Fily took advantage of France's eased coronavirus lockdown this week to see some old high school friends after two months shut away in her home in Brittany. But there was one big thing missing from her gathering: a peck on the right cheek, then a second on the left.

The cheek kiss is fundamental to greetings among friends, colleagues and even national leaders in many countries in Europe. It is also exceedingly ill-suited during the coronavirus pandemic. As Europeans start meeting again with family and friends this month for the first time since the virus swept the world, they are discovering a need to suppress a seemingly inherent reflex.

“We had the instinct to do the peck on the cheek,” said Fily, 30, a civil servant, of the visit at a friend’s house. “But we stopped ourselves. It’s tough.”

Kissing as greeting is a European tradition that can be found all the way back in pre-Christian accounts. Ancient Romans had a precise taxonomy for the level of passion infused in their kisses. In feudal France, vassals pledged loyalty to their lords with a smooch on the lips.

The prevalence of the nonromantic kiss has waxed and waned over the years. The Black Death in the 14th century made it particularly unfashionable, and at the time of the 1918 flu pandemic it tended to be reserved for family members. But recent decades have seen “kiss inflation,” in the words of French sociologist Dominique Picard, with a cheek peck becoming de rigueur among an ever-widening circle of acquaintances.

The practice — whether involving one, two, three or even four kisses — has been especially popular in the countries that rim the Mediterranean, and those, such as Belgium, that are linguistically and culturally tied to them.

The kiss has even sometimes seduced visiting Americans. At a summit in France in August, President Trump exchanged pecks with German Chancellor Angela Merkel and with the wife of French President Emmanuel Macron. First lady Melania Trump, meanwhile, became the subject of Internet memes for her kiss greeting with Canadian Prime Minister Justin Trudeau.

That intimacy now feels as though it were from a different, more tactile time.

“We are a culture of contact, and so we easily touch each other,” said Picard, the author of “Politeness, Good Manners and Social Relations.” “We will stay a civilization that needs some human warmth between people. But I suspect that a lot of people are going to stop kissing each other,” she said of Mediterranean cultures, including her native France.

The kiss is sufficiently ingrained that even some respected doctors say they don’t want to lose it entirely.

“It would be truly sad for the result of the pandemic to be a homogenization of cultures and their traditions,” said Bertrand Kiefer, editor of the Swiss Medical Review. “But even if we start doing it again, it won’t be with the carefree attitude from before the pandemic,” he said, comparing it to the way the AIDS epidemic changed how people have sex.

The kiss briefly survived in the coronavirus era: Macron greeted Italian Prime Minister Giuseppe Conte with double-cheek kisses at a summit in Naples in late February. It was widely viewed as a signal to Europeans that they should not fear their neighbors, even though Italy was already turning into a hot spot for the virus.

But Macron more recently has made a point to appear in public wearing a face mask and to model proper social distancing behavior.

In Italy, the nation’s civil protection chief, Angelo Borrelli, said almost apologetically at the beginning of the outbreak that the country’s “very florid, very expansive” social life needed to stop. Now, as Italy reemerges from lockdown, people are unsure how they should interact.

On street corners in Rome, in front of coffee shops or in neighborhood piazzas, one can see an ongoing experiment in how to replace the baci and abbracci: With air kisses? Waves? Namastes? Some lean in and tap elbows — a gesture best accompanied by an eye roll, to acknowledge the weirdness.

Gilbert Halaby, a boutique owner, had been worrying for weeks about a restaurateur in her 70s, and about the restaurant itself — a neighborhood institution with simple pastas and typewriter-printed menus. Halaby shouted with joy when he saw her preparing to reopen. In normal times, he would have given her a hug, a kiss.

Instead, he kept a meter away and sprang up and down.

“I love to hug. I love a human touch,” Halaby said. “First moment, after not seeing somebody for a long time. You have to stop yourself.”

He said his goal was to refrain from getting close without “losing the affection.”

Multiple barriers to physical contact are emerging, as Italy begins to reshape itself to the threat of the virus. Many shops require masks and have tape markings on the floor for guidance on distancing. Cafes have installed plexiglass barricades around bars and cashiers. At a major bookstore chain, all employees wear welder-style face guards.

Carlo Carboni, a sociologist at the Polytechnic University of Marche, said he still expected the hugging and kissing to return after the threat of the virus waned.

“Elbow tapping and these other social distance greetings will be but a memory of a circumscribed phase of our lives, I hope,” Carboni said. “It’s not as if the black plague or the Spanish flu managed to change our nature.”

In Spain, which by some measures has been the hardest-hit country in Europe, a new kiss-free normal may pose major challenges, said Daniel Chornet, a professor of cultural communication at Saint Louis University’s Madrid campus.

“Spain is a contact culture. People feel culture deeply,” Chornet said. “They feel bad if they are not able to go on with a ritual or participate in cultural acts.”

Enforcing wide physical distances may be hard, he said, mostly because people may feel embarrassed or uncomfortable being the one who doesn’t kiss.

Chornet said he had urged his 65-year-old mother to refrain from greeting relatives for a Sunday lunch scheduled for next week with two kisses.

“They need to lay down ground rules about how they will communicate nonverbally — in advance,” he said. “In the moment, it will be awkward if some are kissing and some aren’t.”

One team at the University of Alicante Foundation determined that Spaniards are greeting one another most commonly with a head nod these days — and that even wearing face masks, people have been able to convey approachability.

“If a person lowers their chin, it means they are pleased and open and there is a connection,” said Javier Torregrosa, a researcher in nonverbal communication who led the work. “If they raise their chin, it is correct recognition, but without connection or approachability.”

Even within European cultures that have been less attached to the kiss greeting, the idea that pecks may be forbidden stirs some passions.

The British have long been on the fence about how to greet one another. It’s like Brexit: They’re in, they’re out, they can’t quite decide. Urban elites who lunch at the Soho House in London often greet one another with kisses. Mates in a pub in the Liverpool? Not bloody likely.

But the cheek smooch is already being missed.

“We are, by nature, super-passionate about defending anything that is being taken away from us, good or bad,” said Judi James, a body language expert and author of books including “BodyTalk at Work.”

“We were never very good at it, as most of us had no idea which cheek first and how many kisses to plant, but we were throwing ourselves into it with enthusiasm rather than technique,” she said.

Harlan reported from Rome and Rolfe reported from Madrid. Quentin Ariès in Brussels, William Booth in London and Stefano Pitrelli in Rome contributed to this report.