Most of us feel better after spending time outside. We usually credit the clean, fresh air or the bright sunlight. But there is actually something in the dirt itself that changes how your brain works. It is a tiny bacterium called Mycobacterium vaccae, which can serve as an all-natural antidepressant. Mycobacterium vaccae actually lives in healthy soil. When you garden, pull weeds, or even take a stroll through a damp forest, you end up breathing it in or getting it on your skin.

Scientists started looking at this microbe a few years ago. They found that when mice were exposed to it, their brains produced more serotonin. That is the same chemical that antidepressant drugs try to boost. Inside your brain, there is a group of neurons that manage your mood. When M. vaccae enters your system, it signals your immune system. This sets off a chain reaction that tells those neurons to fire. The result? You feel less stressed.

In one study, researchers found that the bacteria had a similar effect on the brain as Prozac. It didn’t just make the subjects “happier”—it actually made them more resilient to stress.

Why Getting Dirty Matters

We live in a very clean world now. At times, it’s almost too clean. We use too much hand sanitizer and stay inside our homes in neighborhoods with paved roads. Because of this, we don’t come into contact with the microbes our ancestors lived with every day.

When we lose touch with the natural soil, our immune systems can get a bit confused. This can lead to more inflammation. And science is starting to show a big link between high inflammation and depression. So, getting your hands in a flower or vegetable bed isn’t just a hobby. It is a way to feed your brain what it needs.

You don’t need to be a master gardener to get the benefits. Here are a few ways to get some Mycobacterium vaccae into your day:

• Plant something small: Even a pot of herbs on a balcony requires you to touch the soil.

• Skip the gloves: If you are weeding, try doing it with your bare hands for a few minutes.

• Walk after it rains: The smell of rain on dry earth is actually caused by soil bacteria. Go for a long walk when the ground is damp.

• Let the kids play: Kids who get muddy often have stronger immune systems and better moods.

This isn’t a “cure” for everything. If you have clinical depression, a little dirt probably won’t replace professional help. But it is a real, scientific reason to stop worrying about the mess. Your brain likes it when you get dirty. It’s a simple way to feel a little more grounded when life feels heavy.