By Kate Samra
Apr 5 2021
You step outside and the sky is dark and rolling with clouds. In the distance, you hear the low rumble of thunder and catch a whiff of something earthy in the air. Believe it or not, what you are smelling is petrichor. What you are smelling is rain.
The name petrichor is derived from the Greek “petra” which means “stone,” and “ichor,” which refers to the mythological blood of gods (Poynton, 2015). It was first formally described in 1964 by mineralogists in Australia (Bear & Thomas, 1964). This ‘earth perfume’ is a combination of naturally occurring compounds from dead and living bacteria, fungi, algae, and plant oils. The primary compounds that contribute to this phenomenon are geosmin, stearic acid, oleic acid, and palmitic acid. While geosmin is mostly what our noses recognize, the accompanying acids make the scent volatile and detectable in the air (Bear & Thomas, 1966; Blanchette, 2015).
Researchers at MIT have theorized that petrichor is produced by the impact of raindrops on plant, soil, and rock surfaces. When the rain hits, they believe, it produces a splash of tiny drops of water that are then suspended in air. This aerosol allows plant oils and other natural compounds to exist in the atmosphere for some time, where our olfactory receptors eventually detect them (Chu, 2014). This is why, when we are downwind from an approaching rainstorm, we can often smell it before the rain falls. It’s not just humans that can detect the onset of rain. A 2001 study showed that a number of animals, from honeybees to dogs, exhibit unusual behavior before a rain shower (Galacgac, 2001).
Petrichor is such a popular aroma that scientists have now isolated its scent, which is widely marketed in oils, perfumes, and candles (Vittal et al., 2019). Not only is petrichor a pleasing fragrance, recent studies have even shown that smells we associate with nature can reduce stress (Hedblom et al., 2019).
But you don’t have to buy a candle to experience the comforting effects of petrichor. You can stroll the grounds of the New York Botanical Garden during a spring drizzle and simply stop and smell...the rain.
