In general, green medicine works in the same way as conventional pharmaceutical drugs. For example, by means of their chemical composition. Herbs contain a large amount of natural chemicals that have biological activity. The World Health Organization states that of 119 pharmaceutical drugs derived from plants, approximately 74% of them are used in modern medicine in ways directly correlated to their traditional uses as green medicine by certain native cultures. Aromatherapy is a unique offshoot of green medicine that employs the medicinal properties found in the essential oils of various plants. Aromatherapy is very effective in the control of bacterial infections of the respiratory system, immune insufficiencies such as the Epstein-Barr virus (a type of herpes virus believed to be the causative agent of infectious mononucleosis) and numerous skin disorders.