Essential oil which is then collected in the receiving vessel. Most oils are distilled in a single process. One exception is "ylang-ylang" ("Cananga odorata") which is purifed through a fractional distillation. The recondensed water is referred to as a hydrosol, hydrolat, herbal distillate, or plant water essence, which may be sold as another fragrant product. Hydrosols include rose water, lavender water, lemon balm, clary sage, and orange blossom water. The use of herbal distillates in cosmetics is increasing. Most citrus peel oils are expressed mechanically or cold-pressed (similar to olive oil extraction). Due to the relatively large quantities of oil in citrus
Essential oil themselves, modern works typically discuss specific chemical compounds of which the essential oils are composed. For example: methyl salicylate rather than "oil of wintergreen". Interest in essential oils has revived in recent decades with the popularity of aromatherapy, a branch of alternative medicine that uses essential oils and other aromatic compounds. Oils are volatilized, diluted in a carrier oil and used in massage, diffused in the air by a nebulizer, heated over a candle flame, or burned as incense. Medical applications proposed by those who sell medicinal oils range from skin treatments to remedies for cancer and often are based