The smell of freshly cut grass is an odour caused by green leaf volatiles (GLVs) released when it is damaged. Mechanical damage to grass from activities such as lawnmowing results in the release of cis-3-hexenal and other compounds that contribute to a grassy or "green" smell. cis-3-Hexenal has a low odour detection threshold that humans can perceive at concentrations as low as 0.25 parts per billion.
The GLVs responsible for the smell of freshly cut grass play a role in plant communication and plant defence against herbivory, functioning as a distress signal warning other plants of imminent danger and, in some instances, as a way to attract predators of grass-eating insects. For humans, the smell of freshly cut grass is connected through olfactory memory to past experiences involving the odour and may evoke nostalgia, eliciting associations with spring or summer.