Aromatherapy is the use of essential oils and other aromatic compounds from plants to affect someone's mood or health.

Because aromatherapy is somewhat of an umbrella term, more than one theory of its operation exists. The presence of multiple traditions has led to confusion on just what aromatherapy is.

In the Anglo-Saxon world, among alternative practitioners such as herbalists or naturopaths, aromatherapy is regarded as a complementary modality. The theories offered range from the purported psychological effects of aromas to metaphysical beliefs viewed as pseudoscience by mainstream science. Some proponents of aromatherapy believe that the claimed effect of each type of oil is not caused by the chemicals in the oil interacting with the senses, but that the oil contains a distillation of the "life force" of the plant from which it is derived that will "balance the energies" of the body and promote healing or well-being by purging negative vibrations from the body's energy field. Arguing that there is no scientific evidence that healing can be achieved, and that the claimed "energies" even exist, many skeptics reject this form of aromatherapy as pseudoscience or even quackery.

On the continent, especially in France, where it originated, aromatherapy is based on the pharmacological properties of essential oils. There, aromatherapy is incorporated into mainstream medicine and the use of the anti-septic properties of oils in the control of infections is emphasized over the more "touchy feely" approaches familiar to English speakers. In France some essential oils are regulated as prescription drugs, and thus administered by a physician. In many countries they are included in the national pharmacopeia, but up to the present moment aromatherapy as science has never been recognized as a valid branch of medicine in the United States, Russia, Germany, or Japan.

When aromatherapy is used for the treatment or prevention of disease, a precise knowledge of the bioactivity and synergy of the essential oils used, knowledge of the dosage and duration of application, as well as, naturally, a medical diagnosis, are required.

Essential oils, phytoncides and other natural VOCs work in different ways. At the scent level they activate the limbic system and emotional centers of the brain. When applied to the skin (commonly in form of "massage oils" i.e. 1-10% solutions of EO in carrier oil) they activate thermal receptors, and kill microbes and fungi. Internal application of essential oil preparations (mainly in pharmacological drugs; generally not recommended for home use apart from dilution - 1-5% in fats or mineral oils, or hydrosoles) may stimulate the immune system.