It’s science, y’all!

Meghan Overdeep
August 21, 2018

It turns out your affection for the smell of rain isn’t a quirky personality trait after all. That pleasant, earthy scent unleashed by a downpour has a name, and it’s the result of a reaction between the soil and the rain. And, spoiler alert: it makes everyone smile.

This phenomenon is known as petrichor, and it’s caused by the release of specific chemicals when the rain reaches the ground. One of these chemicals, geosmin, is secreted by soil-dwelling bacteria known as actinomycetes, and is especially common in moist, wooded areas. These bacteria play a pivotal role in decomposition, breaking down organic materials and providing nutrients to soils.

The force of rain drops landing on the ground sends these dormant spores up into the moist air, and into our noses. “It’s a very pleasant aroma, sort of a musky smell,” soil specialist Bill Ypsilantis told NPR. “You’ll also smell that when you are in your garden and you’re turning over your soil.”

It’s a smell we all know well. That’s because, according to Smithsonian, the human nose is extremely sensitive to geosmin, to the extent that some people can detect it at concentrations as low as five parts per trillion.

Actinomycetes flourish in wet conditions and produce spores during dry spells, making the smell of geosmin more pronounced when it rains for the first time in a while, due to the fact that the spores have had time to build up in the soil.

So, there you have it! That romantic post-rain smell is actually just bacteria secretions. Sorry, y’all! But the next time you find yourself inhaling a big gulp of geosmin, take comfort in the fact that you’re surrounded by good, healthy soil.