Jason E. Andersen

We’ve gotten some much-welcomed rain here the last week. During one particular shower I was standing in the back yard, encouraging one of our dogs to pee (she doesn’t like to go in the rain). During the wait, I had a thought that I imagine most people ages 3 and up have had — why does the rain smell like it does?

Bonus Fun Fact: The familiar earthy smell of rainfall comes from the moistening of the soil. Specifically, it comes from the moistening of the organic goo contained in the soil, including all the bacteria, fungi, and plants, along with their various excretions. As the soil moistens with increased humidity of the air or by direct rainfall, the activity of soil bacteria and other organisms increases. A portion of the organic substances they produce is aerosolized into the air and makes its way to your nose. Often times, the smell can be pushed well-ahead of rainfall by winds, creating that ‘coming storm’ smell. 

Also consider that the smell of rain (which we now know is actually the smell of moist bacteria excretions) is more pronounced after a period of drying. This is because the drying of the soil causes soil organisms to go into a period of low activity, thereby creating less by-products. They lie in wait for a rain to come so they can jump into action.

Bonus Bonus Fun Fact: The term for the musky, earthy smell in the air during a rain is ‘petrichor.’ Scientists love to make terms for everything.