JOHN YANG: Giving someone a hand with their car, a simple thank you to a cashier.

These acts of kindness, whether big or small, can have a huge effect on others.

Ali Rogin is back with a look at insights into the power of these acts of kindness.

LORELEI COLBERT, Diagnosed With Breast Cancer: If we've learned anything through this journey, it's coming together and taking on those little moments, appreciating the little things.

ALI ROGIN (voice-over): Three years ago, Lorelei Colbert was diagnosed with an aggressive form of breast cancer.

LORELEI COLBERT: I was facing a very scary diagnosis at the age of 28.

And it came out of nowhere.

When you get a diagnosis like that.

It shifts your perspective on a lot of things.

And for me, it was just tapping into how do I want to live.

ALI ROGIN (voice-over): On her first day of chemo, she set a goal to channel her pain into purpose and inspire the community around her to do the same.

So she turned to social media and encouraged her friends, family and anyone else who wanted to join in to simply be kind to one another.

LORELEI COLBERT: What I'm challenging everyone to do is please uplift me with acts of good.

ALI ROGIN (voice-over): She called it the Chemo to Kindness Challenge.

Over 16 weeks of treatment, these individual acts became a movement.

LORELEI COLBERT: We are at 1,127 acts of kindness around the world.

It could be anything from opening the door for a stranger.

It could be calling your mom, calling your grandmother making a donation to a nonprofit.

We had some teachers do lessons on kindness in elementary schools, and I had students helping their mothers, their brothers, they were dropping off cookies to neighbors.

ALI ROGIN (voice-over): Along the way, Colbert became more and more interested in the science behind these acts of kindness.

LORELEI COLBERT: I learned that acts of kindness, raise the oxytocin levels in you.

So if you're performing an act of kindness, or you're paying it forward to someone else, it's science that your body is getting that wave of love that wave of happiness.

ALI ROGIN (voice-over): UCLA scientist Naomi Eisenberger studies brain activity during an act of kindness.

NAOMI EISENBERGER, Professor, UCLA: What we found is that even in the height of COVID two or three acts of kindness a week seem to significantly reduce levels of depression and anxiety.

ALI ROGIN (voice-over): One study Eisenberger worked on looked at acts of kindness between romantic partners.

NAOMI EISENBERGER: When we look at what's going on neurally for the person who's providing this kind act who's helping their partner, we see increased activation in certain reward related regions.

These are regions like the ventral striatum and the central area.

And so the idea here is that maybe there's something rewarding about actually being able to help a loved one.

AMIT KUMAR, University of Texas: That turns out that interacting with other people can often be a powerful source of happiness.

So being kind to other people can improve our well-being.

ALI ROGIN (voice-over): Amit Kumar studies kindness and its impacts as part of his research at the University of Texas.

AMIT KUMAR: The main question that we were testing is whether these acts of kindness actually go even further than people anticipate.

What was interesting to me as a happiness researcher is that that people have lots and lots of opportunities for being kind to other people doing things that are going to make them happy, or that are likely to make them happy, that they don't always take advantage of.

ALI ROGIN (voice-over): Kumar study found that receivers of acts of kindness felt better than expected, and the givers of kindness were happier than before the act.

AMIT KUMAR: What we find is that performers have an act of kindness, or thinking about whatever it is they're giving, how much would someone like a cupcake?

Or how much would someone like a hot chocolate or an item like that from someone else, as a random act of kindness tends to give the recipient something beyond the cupcake or the hot chocolate itself, it suggests that someone cares about them that someone wanted them to feel good that someone wanted them to feel happy.

ALI ROGIN (voice-over): The study also found that people consistently undervalued the impact of their kindness on others.

AMIT KUMAR: What people told us is that they wanted to perform more random acts of kindness in their lives.

So if this is something that we want to be doing more often, if it's something that makes us feel better, why aren't we doing it?

Well, one of the reasons is because we think it might not matter as much as it actually does.

ALI ROGIN (voice-over): Lorelei Colbert has been cancer free for nearly two years.

But the impact of her kindness challenge remains.

LORELEI COLBERT: People feel better.

You can make a big difference by doing one act of good.

I think it has the power to save a life.

And I think when we all take a little bit of accountability, to say if I do this one act of good, I can really impact others.

It will make our world a much better place to be.

ALI ROGIN (voice-over): The phrase kindness is contagious, might be a cliche, but it turns out, it's also backed by science.

For PBS News Weekend, I'm Ali Rogin.