Free radical activity in our bodies is related to inflammation, aging, and carcinogenesis. Our bodies have various anti-oxidative systems (free radical scavenging activity - FRSA) for preventing oxidative stress.

A 2007 clinical study published in Psychiatry Research, revealed that the FRSA values were increased by low concentrations of lavender essential oil, or by high-concentrations of rosemary essential oil. Both lavender and rosemary essential oils decreased cortisol levels. Rosemary essential oil showed a significant reduction of cortisol levels as increasing amounts of Rosemary essential oil was added.