All of the terpene essential oils are anti-microbial. At one time various essential oils and their constituent terpenoids were applied in allopathic for combating infections, particularly those of the bronchial and urinary tracts, and in preventing sepsis of burns and wounds. Some of these oils still find extensive application as disinfectants, as the anti-septic activity of these oils often exceeds that of phenol, for example thymol is about 20 times more efficacious than phenol. Thymol and carvacrol are used extensively in mouth washes, and various monoterpenoids are incorporated in tooth-pastes, in which their mild anti-septic properties coupled with their rubefacientaction on the gums are beneficial. Much clinical work is underway with these oils, mainly in France. Unfortunately not much of this has been translated into English. Perhaps the best of the French material yet translated, rich in relevant, practical information for the phyto-therapist :
Valney, J. (1982). The Practice of Aromatherapy. C.W.Daniel, SaffronWalden
Comparison of the anti-septic strength of essential oils and phenol is illuminating. This chart is taken from Valnet :
Oil Dose sterilizing 1L of cultured meat stock
Sweet Orange 1.2cc
Lemon Grass 1.6cc
Chinese Cinnamon 1.7cc
Rose Geranium 2.5cc
Chinese Anise 3.7cc
Cinnamon (Singhalese) 4.0cc
Wild Thyme 4.0cc
Juniper Berries 6.0cc
Sweet Fennel 6.4cc
These oils are important in the therapy and prevention of a range of diseases caused by fungi, insects and intestinal worms. For example, thymol inhibits not only bacterial growth but also the growth of yeast and molds. It is used in laboratories for the preservation of urine and other easily perishable specimens. It was a component of some pharmaceutical helminthicides. Among the monoterpenoids, ascaridole especially has found clinical use as an anthelminticagent. Ascaridole is the chief constituent of Chenopodium oil (American wormseed oil), which until quite recently was an official anthelmintic. It is effective against several types of parasitic intestinal worms in humans, especially against roundworms, but also hookworms. Because of its high toxicity, Chenopodium oil and ascaridole are seldom used in human medicine, but are used in veterinary medicine against certain liver flukes.
Several essential oils possess insect-repellent properties. The best known example is citronellal. On the other hand, a number of monoterpenoids possesses a pronounced attraction for certain insects, and it is probable that the combination of attractant and repellent properties of essential oils plays a role of considerable importance in the vegetable kingdom, just as their mild antibacterial and antifungal properties serve to protect the plant against noxious bacteria and fungi.
For a detailed examination of the theory and practice of utilizing essential oils for the treatment of infections please consult the above referenced text by Dr. Valnet.