Aromatherapy

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.

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
Some of the materials employed include:

Essential oils from distillation (e.g. eucalyptus oil) or expression (grapefruit oil) 
Absolutes, oils extracted by solvent or supercritical fluid extraction (e.g. rose absolute) 
Hydrosols, aqueous by-products of the distillation process (e.g. rosewater) 
Infusions, aqueous solutions of plant material (e.g. infusion of chamomile) 
Phytoncides, natural volatile organic compounds from plants 
Carrier oils used to dilute essential oils for use on the skin (e.g. sweet almond oil) 

Theory
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. 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 or Gernany.

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, urine secretion, may have antiseptic activity etc. Different essential oils have very different activity; they are studied in pharmacology and aromachology.

It is significant to note the concept of chemotype in essential oil chemistry. Eucalyptus, for example, has many species, such as Eucalyptus globulus (main component is 1,8 cineole), Eucalyptus citriodora (citral), Eucalyptus menthol, and others. Properties of the essential oils of the same generic (common) name are not all the same; they can differ widely in their chemical components and in their therapeutic actions. Likewise, their chemical makeup depends on the method of extraction (e.g. pressed and distilled bergamot oil have different uses). The practitioner must be aware of these factors.

For medicinal aromatherapy the essential oil specification must meet the following criteria:

Full botanical name of the plant (e.g. Wild mint oil from Mentha arvensis) 
Type of extraction method: essential oil, absolute, СО2-extract, cold pressing (e.g. Rose oil—absolute, or Rose—essential oil) 
Chemotype of the plant—noting the species or cultivar of the raw material (e.g. Rosemary essential oil—camphor type) 
Part of the plant used (e.g. Cinnamon essential oil—Ceylon type from leaves) 
Grade, if manufacturers traditionally use such gradation (e.g. Ylang-ylang essential oil, the premium grade). Reputable aromatherapists insist on pharmaceutical grade that is a higher grade than oils suitable for perfumery or flavoring or other non-therapeutic use. 
Indication of any additional processing of the oil (e.g. Lemon essential oil, deterpenized) 
Main chemical component, when standardized (e.g. Peppermint oil, rectific. 30/35—meaning the menthol content is between 30-35%) 
Country of manufacture—frequently it is possible to deduce from this the composition of the oil (e.g. a batch of Calamus essential oil, India tends to have high azaron content, while Ukrainian samples of Calamus tend to be lower in azaron content) 

Application
While the practice of aromatherapy is sometimes thought to be confined to inhalation, it may include various methods, including:

Inhalation (directly or diffused into the air) 
Absorption through the skin (baths, massages, compresses) 
Absorption through the mucous membranes (oral rinses and gargles) 
Ingestion (occasionally prescribed, with caveats) 

Therapeutic effects
Aromatherapy is based mainly on the following therapeutic effects:

Antiseptic effects: viricidial, bactericidal, fungicidal 
Anesthetic action (menthol, camphor) 
Central nervous system effects 
Metabolic / Endocrine effects 
Psychological effects 
Immunostimulator 
Fragrances can have a relaxing effect measured as an increase in alpha brain waves.

One of the best known essential oils for aromatherapy is lavender, which is recommended by practitioners for treating wounds, to enhance memory, and to aid sleep by combating anxiety and insomnia. Other popular scents include eucalyptus, rose, jasmine and bergamot.

Aromatherapy is among the fastest growing fields in alternative and holistic medicine. Aromatherapy is sometimes used in clinics and hospitals for treatment of pain relief, for labor pain, for relieving pain caused by the side effects of the chemotherapy, and for the rehabilitation of cardiac patients.

Criticism
Skeptics argue that while pleasant scents can be relaxing, lowering stress and related effects, there is currently insufficient scientific proof of the effectiveness of aromatherapy. Like many alternative therapies, few controlled, double-blind studies have been carried out—a common explanation is that there is little incentive to do so if the results of the studies are not patentable. There are some treatments generally accepted in Western medicine to give a form of relief for the airways in case of cold or flu, such as mint and eucalyptus essential oils. Skeptical literature often depicts aromatherapy as based on anecdotal evidence of its benefits rather than proof that aromatherapy can cure diseases. Some skeptics acknowledge that aromatherapy has limited scientific support but argue that its claims go beyond the data or that the studies are not adequately controlled and peer reviewed.

The term "aromatherapy" has been applied to such a wide range of products that almost anything which contains essential oils is likely to be called an "aromatherapy product", rendering the term somewhat meaningless in that context.

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 little scientific evidence that healing can be achieved, or that the claimed "energies" even exist, many skeptics reject this form of aromatherapy as pseudoscience or even quackery.

Even among "natural" practitioners like herbalists or naturopaths, aromatherapy is regarded more as an art form than a valid healing science. At best, it's a complimentary modality; it's seldom the only treatment prescribed.