Geraniol is a phytonutrient in a class of chemicals called terpenes. Terpenes are hydrocarbons, meaning they are made up of hydrogen and carbon, that are produced by a wide variety of plants. A big terpene producer is conifers such as pine, which produce it in resin. The word terpene is derived from the word turpentine. Terpenes contain isoprene units, which are a combination of 5 carbon atoms and 8 hydrogen atoms, and the different types of terpenes are classified according to how many of these isoprene units they contain. Geraniol is a monoterpene, meaning it has two isoprene units in its chemical makeup. It is a clear or pale yellow, oily, rose-scented liquid.
Gardeners and herbalists have known for centuries that geraniums have insect repelling properties, and this is because their oil contains geraniol. Geraniol is now extracted and used to make commercial insect repellant, which is effective against all sorts of critters from mosquitoes, all types of flies, cockroaches and fire ants to fleas, gnats and ticks. Geraniol, like many terpenes, is also used in perfumes and aromatherapy products. It is also an additive used to improve the flavor of some cigarettes. Aged tobacco contains natural geraniol. Honeybees produce geraniol from their glands to mark nectar bearing flowers and to find the entrance to their hives.
Geraniol is an antioxidant, and is being studied for its abilities to suppress tumour growth. In 1995 the Journal of Nutrition reported that geraniol suppressed the growth of hepatomas and melanomas transplanted to rats and mice. The journal Lipids, published by the American Oil Chemists' Society, published a study in February of 1997 showing that several terpenes, including geraniol, suppressed pancreatic tumour growth without affecting blood cholesterol levels. In 2001 The American Society for Pharmacology and Experimental Therapeutics published a study showing that geraniol inhibits growth in human colon cancer cells.
The Herb Companion has more details on studies done with geraniol and tumour suppression.
Geraniol can be found in bergamot (an ingredient of Earl Grey tea), carrots, coriander, lavender, lemon, lime, nutmeg, orange, rose, blueberries and blackberries. Geraniums also have this essential oil in large enough quantities to be used commercially. Aromatherapy clinics claim that inhaling geranium scent lowers or raises blood pressure a few points, and use it to control depression and mental disturbances. Herbalists use geranium as a skin therapy, in the form of a salve or massage oil, to treat eczema, burns, stretch marks, fungus, acne and inflammation. Geraniums are unusual among scented flowers because the scent is actually in the leaves, rather than the flower.