As you might recall from high school health class, the parasympathetic nervous system is responsible for our body’s rest-and-digest response. It balances out the fight-or-fligth response—which is often elicited by stress—and causes our heart rate and blood pressure to slow down and normalize. Essential oils can be used for in-the-moment stress relief when you feel yourself getting worked up, or you can use them more preventatively to stay calm and collected throughout the day. Here are a few strategies for working them into your routine: The more you use a certain oil, the more your brain will start to associate it with releasing stress, so go ahead and smell your way to calm.