Aromatherapy, commonly associated with complementary and alternative medicine (CAM), is the use of volatile liquid plant materials, known as essential oils (EOs), and other aromatic compounds from plants to affect someone's mood or health. The word was coined in the 1920s by French chemist René Maurice Gattefossé, who devoted his life to researching the healing properties of essential oils after a lucky accident in his perfume laboratory. (In the accident, he lit his arm on fire and thrust it into the nearest cold liquid, which happened to be a vat of lavender oil. Much to his amazement, the burn quickly healed without a scar.)

The main branches of aromatherapy include:

• Home aromatherapy (self treatment, perfume & cosmetic use)
• Clinical aromatherapy (as part of pharmacology and pharmacotherapy)
• Aromachology (the psychology of odors and their effects on the mind)

Materials

• Essential oils: Fragrant oils extracted from plants chiefly through distillation (e.g. eucalyptus oil) or expression (grapefruit oil). However, the term is also occasionally used to describe fragrant oils extracted from plant material by any solvent extraction.
• Absolutes: Fragrant oils extracted primarily from flowers or delicate plant tissues through solvent or supercritical fluid extraction(e.g. rose absolute). The term is also used to describe oils extracted from fragrant butters, concretes, and enfleurage pommades using ethanol.
• Phytoncides: Various volatile organic compounds from plants that kill microbes. Many terpene based fragrant oils and sulfuric compounds from plants in genus "Allium" are Phytoncides, though the latter are likely less commonly used in aromatherapy due to their disagreeable smells.
• Hydrosols: The aqueous by-products of the distillation process (e.g. rosewater). Hydrosol used are limited to plants such as rose and camomile since most hydrosols have unpleasant smells.
• Infusions: Aqueous extracts of various plant material (e.g. infusion of chamomile)
• Carrier oils: Typically oily plant base triacylglycerides that are used to dilute essential oils for use on the skin (e.g. sweet almond oil)