Monoterpenes are a class of compounds grouped together due to their structural similarities. Monoterpenes may be isolated from a large number of sources including yarrow and horehound. Some examples of monoterpenes are camphene, limonene, and pinene. Monoterpenes have a wide variety of properties; for example, limonene is antibacterial, antiviral, and a skin irritant; pinene is antimicrobial.
Leung, Albert Y. 1980. Encyclopedia of Common Natural Ingredient used in Food, Drugs and Cosmetics. John Wiley and Sons, NY. 409.
Stedman, Thomas Lathrop. Stedman's Medical Dictionary. 24th edition. Baltimore: Williams and Wilkins, 1982.
Windholz, Martha, Susan Budavani, et.al. 1976. The Merck Indes. Merck and Co., Inc. New Jersy.