Throughout history, essential oils have been used to treat a variety of ailments, including relieving minor pain, dissolving kidney stones, preventing flatulence and helping with childbirth. In addition, some essential oils are known to have preservative properties. Interest in essential oils as a health tool has grown in recent decades with the popularity of aromatherapy. Aromatherapy is the practice of claiming the curative effects of essential oils and other aromatic compounds. In order to use essential oils for aromatherapy applications, they are diluted in the carrier oil. This dilution is important to properly reduce the concentration of the essential oil, as the pure essential oil is so potent that it can burn the skin if used alone. Once the essential oil is diluted, it can be used for massage, diffused into the air through a spray, heated over a candle flame, or burned as incense. Although essential oils are mainly formulated from carrier oils, they are sold separately due to their different uses.