Being cynical may seem harmless, or even safer than trusting others, but that's far from the truth, according to Jamil Zaki, an associate professor of psychology at Stanford University. He is the author of the new book "Hope for Cynics: The Surprising Science of Human Goodness."

Cynicism is "the belief that humanity in general is selfish, greedy and dishonest," Zaki tells CNBC Make It, and it can be harmful for your health.

"Cynics tend to be more depressed [and] anxious. They suffer from more addiction. But it's also physical. Cynics tend to suffer from more heart disease [and] more diabetes. They even die younger than non-cynics," Zaki says.

If you're worried that not being cynical means you'd be naïve, it's important to know that the opposite of cynicism isn't trusting just any and everyone, Zaki notes.

"Of course, there are benefits to not trusting people in lots of situations, but cynicism is deciding not to trust anybody. It's a blanket theory about all people, and it's very hard to understand how something like that could help us," he says.

Here are three statements that Zaki says, if you agree with them, may indicate that you are a cynic. Plus, his advice he has for how to reverse cynicism and why it's important to do so.

If you agree with these 3 statements, you might be a cynic

1. No one cares much what happens to you.
2. Most people dislike helping others.
3. Most people are honest chiefly through fear of getting caught.

"If you disagree with all three, you're probably low in cynicism. If you agree with just one, you're on the low-​medium end—think medium-​rare for a steak," Zaki wrote in his book.

"If you agree with two, you're on the medium-​high end. And if you agree with all three, you might be a well-​done cynic, with a bleak 'theory of everyone.'"

In the 1950s, psychologists Walter Cook and Donald Medley came up with an assessment that included 50 statements, prompting teachers to indicate if they agreed or disagreed with them, in an attempt to identify good teachers. The three above statements are pulled from Cook and Medley's list.

"The more a teacher agreed [with the statements], the worse their rapport with students," Zaki wrote. "The more statements anyone agreed with, the more suspicious they were of friends, strangers, and family."

3 practices to reverse cynicism and become more hopeful

"The first thing is to want to give [cynicism] up. If you do, then there's a couple of things that you can try," Zaki says.

To reverse cynicism and be more trusting of the good in people and positive outcomes:

• Stop glamorizing the idea of cynicism: "Being really negative doesn't make you right, doesn't make you wise, it doesn't keep you safe, and it doesn't make you moral," Zaki says.
• Try to be more like a scientist: Search for evidence to prove, or disprove, the negative beliefs you have. "When you find yourself making blanket judgments about people or distrusting folks that you've just met, ask yourself, fact-check that impulse [and] say, 'Why am I feeling that way?'"
• Give people a chance to show you who they are: This requires taking leaps of faith and calculated risks to learn what people are like before assuming how they are. "We underestimate how trustworthy, generous, friendly and open minded people are," Zaki says. "That's not to say there are not jerks out there. Of course there are, but the average person underestimates the average person."

When you follow these practices, you can develop a sense of hope, Zaki says. It "turns out that hope is incredibly valuable for our health, and it's especially important when we face adversity."

Hopeful people with chronic illnesses experience less depression, students from lower socioeconomic backgrounds who have hope tend to "tend to see their academic goals more clearly and pursue them more fiercely," and hope is often at the center of social movements, he explains.

"Hope [is] not a sort of complacent, rosy feeling, but rather a yearning for something better that improves our health, strengthens our relationships and communities, and actually is a force for social change."

Are you stressed about money? Sign up for CNBC's new online course. We'll teach you how to be more successful and confident with your money, and practical strategies to boost savings, get out of debt and invest for the future. Start today and use code EARLYBIRD for an introductory discount of 30% off through September 2, 2024.

Plus, sign up for CNBC Make It's newsletter to get tips and tricks for success at work, with money and in life.