Petrichor is the pleasant, earthy smell that rises from the ground when rain falls after a long dry spell. If you've ever stepped outside during the first rain after weeks of hot, dry weather and noticed that distinctive fresh scent, you've experienced petrichor.

The smell comes from oils that plants release during dry periods. These oils soak into soil and rocks, then mix with a chemical called geosmin that certain bacteria produce. When raindrops hit the ground, they release these trapped scents into the air as a fine mist. The bigger and faster the raindrops fall, the stronger the petrichor becomes.

Many people find petrichor calming and refreshing. After a hot summer day, that first rain brings relief, and petrichor is part of what makes that moment feel so good. Some perfume makers even try to capture the scent in bottles, though most people agree nothing quite matches the real thing.