From a scientific perspective, essential oils are small organic molecules that change quickly from a liquid to a gas state when they reach room temperature. This is why bottled essential oils are so powerful. A bottle of essential oil contains tiny molecules in a liquid state. When you unscrew the cap and open the bottle, the molecules change quickly from a liquid to a gas, which is why you can smell the oil immediately—even from a distance.
Essential oil molecules are often referred to as “volatile aromatic compounds.”
These molecules are considered volatile because of how quickly they change from a liquid to a gas. Because they’re so volatile, the chemical compounds in essential oils can move quickly through the air until they come into contact with special sensors in the nose.
The benefits of each essential oil are largely determined by the kind of plant it comes from and the chemical properties it contains. An oil might be cleansing, refreshing, or boosting to the immune system—among any number of other benefits—depending on its chemical profile and origin plant.