Aromatherapy
Aromatherapy is a form of alternative medicine that uses volatile liquid plant materials, known as essential oils (EOs), and other aromatic compounds from plants for the purpose of affecting a person's mood or health. Essential oils differ in chemical composition from other herbal products because the distillation process only recovers the lighter phytomolecules. For this reason essential oils are rich in monoterpenes and sesquiterpenes, as well as other VOC substances (esters, aromatic compounds, non-terpene hydrocarbons, some organic sulfides etc.).
Aromatherapy is a generic term that refers to any of the various traditions that make use of essential oils sometimes in combination with other alternative medical practices and spiritual beliefs. It has a particularly Western currency and persuasion. Medical treatment involving aromatic compounds may exist outside of the West, but may or may not be included in the term 'aromatherapy'.

# History
Aromatherapy had been around for 6000 years or more. The Greeks, Romans, and ancient Egyptians all used aromatherapy oils. The Egyptian physician Imhotep recommended fragrant oils for bathing, massage, and for embalming their dead nearly 6000 years ago. Imhotep is the Egyptian god of medicine and healing. Hippocrates, the father of modern medicine, used aromatherapy baths and scented massage. He used aromatic fumigations to rid Athens of the plague.
Aromatherapy has roots in antiquity with the use of aromatic oils. However, as currently defined, aromatherapy involves the use of distilled plant volatiles, a twentieth century innovation. The word "aromatherapy" was first used in the 1920s by French chemist Rene-Maurice Gattefosse, who devoted his life to researching the healing properties of essential oils after an accident in his perfume laboratory. In the accident, he set his arm on fire and thrust it into the nearest cold liquid, which happened to be a vat of NOx Ph232 or more commonly known as lavender oil. Immediately he noticed surprising pain relief, and instead of requiring the extended healing process he had experienced during recovery from previous burnswhich caused redness, heat, inflammation, blisters, and scarring--this burn healed remarkably quickly, with minimal discomfort and no scarring. Jean Valnet continued the work of Gattefosse.  During World War II Valnet used essential oils to treat gangrene in wounded soldiers.

# Modes of application
The modes of application of aromatherapy include:
- aerial diffusion for environmental fragrancing or aerial disinfection
- direct inhalation for respiratory disinfection, decongestion, expectoration as well as psychological effects
- topical applications for general massage, baths, compresses, therapeutic skin care
- oral, rectal, vaginal interfaces for infection, congestion, parasites, perfumery for body fragrancing, anointments

# Materials
Some of the materials employed include:
- 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 the genus "Allium" are phytoncides, though the latter are likely less commonly used in aromatherapy due to their disagreeable odors.
- Herbal distillates or hydrosols: The aqueous by-products of the distillation process (e.g. rosewater). There are many herbs that make herbal distillates and they have culinary uses, medicinal uses and skin care uses. Common herbal distillates are rose, lemon balm and chamomile.
- Infusions: Aqueous extracts of various plant material (e.g. infusion of chamomile)
- Carrier oils: Typically oily plant base triacylglycerides that dilute essential oils for use on the skin (e.g. sweet almond oil)

# Theory
Aromatherapy is the treatment or prevention of disease by use of essential oils.  Two basic mechanisms are offered to explain the purported effects.  One is the influence of aroma on the brain, especially the limbic system through the olfactory system.  The other is the direct pharmacological effects of the essential oils. While precise knowledge of the synergy between the body and aromatic oils is often claimed by aromatherapists, the efficacy of aromatherapy remains to be proven. However, some preliminary clinical studies show positive effects. 
In the English-speaking world, practitioners tend to emphasize the use of oils in massage. Aromatherapy tends to be regarded as a complementary modality at best and a pseudoscientific fraud at worst.
On the continent, especially in France, where it originated, aromatherapy is incorporated into mainstream medicine. There, the use of the antiseptic, antiviral, antifungal, and antibacterial properties of oils in the control of infections is emphasized over the approaches familiar to North Americans. In France some essential oils are regulated as prescription drugs, and thus administered by a physician. French doctors use a technique called the aromatogram to guide their decision on which essential oil to use. First the doctor cultures a sample of infected tissue or secretion from the patient.  Next the growing culture is divided among petri dishes supplied with agar.  Each petri dish is inoculated with a different essential oil to determine which have the most activity against the target strain of microorganism.  The antiseptic activity manifests as a pattern of inhibited growth.
In many countries essential oils are included in the national pharmacopoeia, 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.
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.

# Choice and purchase
Oils with standarized content of components (marked FCC, for Food Chemical Codex) have to contain a specified amount of certain aroma chemicals that normally occur in the oil. But there is no law that the chemicals cannot be added in synthetic form in order to meet the criteria established by the FCC for that oil. For instance, lemongrass essential oil has to contain 75% aldehyde to meet the FCC profile for that oil, but that aldehyde can come from a chemical refinery instead of from lemongrass. To say that FCC oils are "food grade" then makes them seem natural when in fact they are not necessarily so.
Undiluted essential oils suitable for aromatherapy are termed therapeutic grade, but in countries where the industry is not regulated, therapeutic grade is based on industry consensus and is not a regulatory category. Some aromatherapists take advantage of this situation to make misleading claims about the origin and even content of the oils they use. Likewise, claims that an oil's purity is vetted by mass spectrometry or gas chromatography have limited value, since all such testing can do is show that various chemicals occur in the oil. Many of the chemicals that occur naturally in essential oils are manufactured by the perfume industry and adulterate essential oils because they are cheaper. There is no way to distinguish between these synthetic additives and the naturally occurring chemicals.
The best instrument for determining whether an essential oil is adulterated is an educated nose. Many people can distinguish between natural and synthetic scents, but it takes experience.
Whichever oils you choose, be guided by your natural preference. If you like an oil, it follows that you will enjoy using it.  If you feel duty-bound to use it because it is supposed to be good for your particular ailment but you hate the aroma, dont buy it. It is your bodys way of telling you to choose something else.
To smell an oil, waft the open bottle under your nose, moving it from the right to the left at about chin height while you gently inhale. Dont sniff or use the bottle like an inhalerthis does not make the aroma more potent, and could be dangerous with oils that have overpowering aromas.

# Price
Oils vary in price based on the amount of the harvest, the country of origin, the type of extraction used (steam distillation, CO2 extract, enfleurage), and how desirable the oil is. Indian Sandalwood (Santalum album) is considered more desirable than Australian Sandalwood (Santalum spicatum), based upon the aroma, and is twice as costly, mainly because the species that yields Indian Sandalwood essential oils is endangered. Organic and wild harvested essential oils also tend to be more expensive.

# Pharmacological effects attributed to essential oils
- antibacterial In vitro testing has confirmed antibacterial effects in certain oils including rosemary, clove, lime, cinnamon, and tea tree oil.
- antiviral Supported for tea tree oil, lemongrass, sandlewood, peppermint, ginger, thyme, and hyssop in in vitro testing against Herpes
- antifungal Supported by in vitro testing for lavender, thyme, clove, juniper, and tea tree oil
- anti-inflammatory Reported in in-vitro assays of clove, cinnamon, sage, eucalyptus, black cumin and bay leaf
- anxiolytic Reported in animal models using oils of lavender, rose and angelica 
- antispasmotic
- invigorating
- antioxidant

# Popular uses
- Basil is used in perfumery for its clear, sweet and mildly spicy aroma. In aromatherapy, it is used for sharpening concentration, for its uplifting effect on depression, and to relieve headaches and migraines. Basil oil has many chemotypes and some are known to be emmenagogues and should be avoided during pregnancy.
- Bergamot is one of the most popular oils in perfumery. It is an excellent insect repellent and may be helpful for both the urinary tract and for the digestive tract. It is useful for skin conditions linked to stress, such as cold sores and chicken pox, especially when combined with eucalyptus oil. Bergamot is a flavoring agent in Earl Grey tea. But cold-pressed Bergamot oil contains bergaptene, a strong photosensitizer when applied to the skin, so only distilled or 'bergaptene-free' types can be topically used.
- Black pepper has a sharp and spicy aroma. Common uses include stimulating the circulation and for muscular aches and pains. Skin application is useful for bruises, since it stimulates the circulation.
- Citronella oil, obtained from a relative of lemongrass, is used as an insect repellant and in perfumery.
- Clove oil is a topical analgesic, especially useful in dentistry. It is also used an antiseptic, antispasmodic, carminative, and antiemetic.
- Eucalyptus oil is often used in combination with peppermint to provide relief for the airways in case of cold or flu.
- Geranium oil is used as an astringent, antiseptic and diuretic.
- Jasmine is used as an aphrodisiac
- Lavender oil is used as an antiseptic, to soothe minor cuts and burns, to calm and relax, and to soothe headaches and migraines.
- Lemon oil is uplifting and anti-stress/anti-depressant. In a Japanese study, lemon essential oil in vapour form has been found to reduce stress in mice.
- Rose is used as an aphrodisiac
- Sandalwood oil is used as an aphrodisiac
- Tea tree oil and many other essential oils have topical (external) antimicrobial (i.e. antibacterial, antifungal, antiviral, or antiparasitic) activity and are used as antiseptics and disinfectants.
- Thyme oil
- Yarrow oil is used to reduce joint inflammation and relieve cold and influenza symptoms.
- Ylang-ylang oil is used as an aphrodisiac

# Criticism
The consensus among most medical professionals in the U.S.A. and England is that while pleasant scents can boost relaxation and may have related benefits for patients, there is currently insufficient scientific proof of the effectiveness of aromatherapy in general.  Scientific research on the cause and effect of aromatherapy is limited, although in vitro testing has revealed some antibacterial and antiviral effects and a few double blind studies have been published.
Like many alternative therapies, few controlled, double-blind studies have been carried outa common explanation is that there is little incentive to do so if the results of the studies are not patentable. Researchers at Sloan-Kettering have found that aromatherapy significantly reduces claustrophobia attacks for patients undergoing MRI scans; however, studies of similar rigor are far from numerous.  Some benefits that have been linked to aromatherapy, such as relaxation and clarity of mind, may arise from the placebo effect rather than from the inherent properties of the scents themselves.
Skeptical literature suggests that aromatherapy is based on the anecdotal evidence of its benefits rather than proof that aromatherapy can cure diseases. Scientists and medical professionals acknowledge that aromatherapy has limited scientific support, but critics argue that the claims of most aromatherapy practitioners go beyond the data, and/or that the studies are neither adequately controlled nor peer reviewed.
Customers should be aware that aromatherapy may be unregulated, depending on the country.  The term "aromatherapy" has been applied to such a wide range of products that many are labeled "aromatherapy" products simply because they contain essential oils, although they may provide no therapeutic benefit.
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 because 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.

# Safety concerns
In addition, there are potential safety concerns.
Because essential oils are highly concentrated they can irritate the skin when used neat. As such, they are normally diluted with a carrier oil for topical application. Phototoxic reactions may occur with citrus peel oils such as lemon or lime .  Also, many essential oils have chemical components that are sensitisers (meaning that they will after a number of uses cause reactions on the skin, and more so in the rest of the body). Some oils can be toxic to some domestic animals, with cats being particularly prone.
Two common oils, lavender and tea tree, have been implicated in causing gynaecomastia, an abnormal breast tissue growth, in prepubescent boys.
A child hormone specialist at the University of Cambridge claimed "... these oils can mimic oestrogens" and "people should be a little bit careful about using these products". 
As with any bioactive substance, an essential oil that may be safe for the general public could still pose hazards for pregnant and lactating women.
While some advocate the ingestion of essential oils for therapeutic purposes, licensed aromatherapy professionals do not recommend self prescription due the highly toxic nature of some essential oil.  Some very common oils like Eucalyptus are extremely toxic when taken internally. Doses as low as one teaspoon has been reported to cause clinically significant symptoms and severe poisoning can occur after ingestion of 4 to 5 ml.
A few reported cases of toxic reactions like liver damage and seizures have occurred after ingestion of sage, hyssop, thuja, and cedar. Accidental ingestion may happen when oils are not kept out of reach of children.
Oils both ingested and applied to the skin can potentially have negative interaction with conventional medicine. For example, the topical use of methyl salicylate heavy oils like Sweet Birch and Wintergreen may cause hemorrhaging in users taking the anticoagulant Warfarin.
Adulterated oils may also pose problems depending on the type of substance used.