Many essential oils have been proven effective against fungi and yeast (tea tree, lavender and geranium), parasites (bergamot) and viruses (cinnamon, thyme and Eucalyptus radiata). Others fight infection with amazing effectiveness, killing bacteria by disrupting their life cycle. According to Dr. Jean-Claude Lapraz, M.D., a specialist in essential oils, most essential oils lower the pH of the blood slightly, creating an inhospitable environment for bacteria, which thrive in an alkaline environment.

Unlike conventional antibiotic drugs, which may cause undesirable side effects, essential oils are "probiotic": they not only kill pathogenic bacteria, but tend to leave beneficial bacteria (intestinal flora) intact. This seems an exclusive prerogative of natural healing and remains a mystery to science. Also, bacteria typically do not acquire a resistance to essential oils, as they so often do to antibiotic drugs.

Essential oils act quickly in the body. Some are detectable in the breath within minutes after application to the skin, and are eliminated from the body within several hours. Repeated applications may be required, especially when treating acute disorders that require keeping a constant level of essential oil active in the body.

Remember that less is more when it comes to aromatherapy. Consistent low doses are safest and most effective.

One advantage of aromatherapy treatments is that they don't need to work their way through the entire body to treat a particular area. Most of the essential oils suggested in this section are intended for dilution in a carrier oil. You can massage these diluted oils directly over the area that needs treatment-on the chest, for example, to treat congested lungs, or on the stomach in cases of indigestion. Application by inhalation or bath is also appropriate for many treatments.

Essential oils are perfectly safe when used in the suggested dilutions, although applications complicated by pregnancy, epilepsy, serious health problems and some medications do call for caution. A patch test is recommended before using any formula. (See Safety Precautions in the "Guidelines" chapter for further information on safety, applications, dilutions and carrier oils; also, please note the various "considerations" in the "Materia Medica" chapter.)

Body Systems
Health and vitality depend on the harmonious and collective functioning of each organ in the body. Therefore, the identification and separation of systems and their association with various oils is a simplification, albeit a necessary one. Also, because most plants have multiple actions, many are listed below for more than one system or symptom.