Politicians lie? Actually, we’re all pretty good at it by age 5.

This is the season of lies.

We watch as candidates for the world’s most powerful job trade falsehoods and allegations of dishonesty. Republican presidential candidate Donald Trump routinely calls rival Ted Cruz “Lyin’ Ted.” Cruz retorts: “Falsely accusing someone of lying is itself a lie and something Donald does daily.”

But it’s not just office-seekers who seem truth-averse. Researchers who examine humanity’s less-than-truthful underbelly are clear: We all stretch the truth. We learned to deceive as toddlers and are quite good at it by age 5. We rationalize our fabrications that benefit us. We daily tell little white lies that make others feel good.

“I feel more worried about lying in public life (specifically by politicians, and in particular, Trump) than I ever have before,” Bella DePaulo, a psychology researcher at the University of California at Santa Barbara, said in an email. When lies succeed, they make it “more tempting to lie. Lies can stick. They can have a lingering effect, even if they are debunked. “

Children learn to lie at about 3 years old, on average, often when they realize that other people don’t know what they are thinking, said Kang Lee, a professor at the University of Toronto who has done extensive research on children and lying.

At age 2, only 30 percent lie, Lee said. At age 3, half do. By 5 or 6, 90 percent of kids lie, and Lee said he worries about the 10 percent who don’t.

In 1996, DePaulo, author of “The Hows and Whys of Lies,” put recorders on students for a week and found that they lied, on average, in every third conversation of 10 minutes or more. For adults, it was once every five conversations.

“I would say we’re lying constantly. Constantly,” said Maurice Schweitzer, who studies deception and decision-making at the University of Pennsylvania’s Wharton School of Business, Trump’s alma mater.

Experts split on whether to count white lies. When your spouse tells you that you don’t look fat in that outfit when you do, does it do any harm?

Some lies, Schweitzer said, “fall under politeness norms and are not very harmful. There are other lies that are self-interested, and those are the ones that are really harmful. Those are the ones that harm relationships, harm trust.”

But DePaulo sees no distinction: “It doesn’t matter if the attempt was motivated by good intentions, and it doesn’t matter if the lie is about something little.”

Regardless, society rewards people for white lies, said Robert Feldman at the University of Massachusetts. “We don’t like people who tell us the truth all the time.”

Students learn to administer polygraph exams at the Latin American Polygraph Institute in Bogota, Colombia. By studying how and why we deceive, the experts say they can help us better understand the 2016 election season. (Fernando Vergara/AP)

He added, “The lies that we accept from politicians right now are lies that are seen as acceptable because it’s what we want to hear.”

Or perhaps we feel that lying is necessary.

“The reason that people want their politicians to lie to them is that people care about politics,” said Dan Ariely, a professor of psychology and behavioral economics at Duke University. “You understand that Washington is a dirty place and that lying is actually very helpful to get your policies implemented.”

When people deceive beyond white lies, they spend a lot of effort justifying and rationalizing what they are doing.

“Dishonesty is contagious,” said the University of Nottingham’s Simon Gaechter, who conducted a study examining honesty in a dice game in 23 countries. The more crooked a society was, based on an international corruption index, the more likely its people were willing to deceive in the simple dice game.

Most people want to be honest, but if they live in a country where rule violations are rampant, “people say, ‘Well, everybody cheats. If I cheat here, then that’s okay,’ ” Gaechter said.

There are also costs to the liar, Lee said, noting studies that measure the effect of deception on the body and brain and how much energy it takes to create and maintain a lie.

“When you tell lies, it costs your brain a heck of a lot more resources than when you tell the truth,” he said.

— Associated Press