Essential oils, also known as volatile oils, are among the most important compounds found in various parts of medicinal plants. These oils are highly volatile, and even at room temperature, they evaporate and are lost to the air when exposed, which is why they are called "volatile oils." Essential oils are generally colorless and are essentially the distinctive fragrance of the plants. However, if they are not stored properly and under suitable conditions, they may gradually oxidize, become resinous, and eventually darken. Therefore, to prevent any negative changes, essential oils should be stored in cool, dry places in opaque, airtight containers, away from light.