Aromatherapy is a form of complementary medicine whose adherents claim it to be a gentle but effective method of healing and enhancing the mind, body, and spirit through the use of essential oils that are derived from aromatic plants, trees, and grasses. It is considered one of the safer forms of complementary therapy, and often a pleasant one. Evidence of efficacy is more difficult to establish.
Claims of specific healing properties are not accepted by mainstream medicine or by conventional scientists, although some clinical trials have been undertaken. Some integrative medicine programs, clinical trials and retrospective analyses combine it with other modalities such as massage and relaxation techniques, where it may be of help in improving subjective well-being. Cautions are made, however, that it is an adjunctive technique. 
In the U.K, however, it is considered a complementary technique used to complement conventional medicine and do not purport to embrace diagnostic skills
History of aromatherapy
As far back as 4500 BC, the Egyptians utilized the power of perfumes. Each Egyptian deity has its own special fragrance, and statues were covered by essential oils. The Egyptians used oils for embalming. Ancient Egyptians are regarded as the founders of aromatherapy.
We also know that ancient Greeks also used to have aromatic bath and scented massage. Hippocrates, who known as the father of medicine, said it was the way to the health.
The ancient Hindu system of medicine, Ayurveda, incorporated plants extracts and essential oils into healing potions.
In 14th century, in Europe, pine was burned in the street and floors are covered by aromatic plants to protect them from infectious disease. From 15th to 17th century several books of herbal remedies were published throughout Europe.
In 19th century, essential oils were widely used in medicine. Many research were developed to look for more information on their healing uses.
The term "aromatherapy" was coined by the French chemisy Rene-Maurice Gattefosse, who used neat lavender oil in a laboratory accident to heal a burn on his hand. He then used essential oils to treat soldiers in hospital during World War I. In the late 1920s and 30s he continued to study essential oils as a healing agent.
In 1948-1959, another French doctor, Jean Valnet, also used essential oils to treat wounds in the Indo-China war. He went on to become the father of aromtherapy and produced a classic text, Aromatherapie, in 1964.
Valnet's work was studied in turn by Marguerite Maury, who created the notion of aromatherapy as it tends to be practised today, with the emphasis on an individual prescription of essential oils to match a person's state of psychological and physical condition. Maury also proposed the use of massage as a means of administering the oils.
The first book in English, The Art of Aromatherapy, by Robert Tisserand was published in 1975. This book has brought together the history on essential oils and a detailed methodology for their uses. This book has been translated into many languages. He also write Essential Oils Safety, which became a manual key to the therapists and practitioners.
When you are learning about aromatherapy, it is important to know the essential oils individually, in terms of their fragrance, properties and uses. However, the second important dimension involves knowing how to blend several oils together in a balanced way.
Complementary and alternative medicine
While some studies showed oils having a calming effect on patients with dementia, those studies combined their use with massage. To try to isolate the effect of the aromas, another study suggested that applying the oils to the skin may be more effective than inhalation.  It should be noted that some essential oils, when not diluted, can cause skin irritations and burns; many retailers of these oils make this a prominent warning.
- Hoffman, Caroline (2007), Benefits of complementary therapies, vol. 9(Suppl 2), DOI:10.1186/bcr1807., at S9
- Select Committee appointed to consider Science and Technology, U.K. Parliament (21 November 2000), Chapter 2: Disciplines examined, Definitions of the Various CAM Therapies, Complementary and Alternative Medicine
- Snow LA, Hovanec L, Brandt J. (2004 Jun), "A controlled trial of aromatherapy for agitation in nursing home patients with dementia.", Altern Complement Med 10(3): 431-7.