Why does Aromatherapy work? Essential oils trigger neurotransmitters in your brain to secrete certain hormones specific to the essential oils properties. Humankind has been acquainted with Aromatherapy for over 5,000 years! There are no harmful side effects from essential oils that are administered properly. In France, today, more than a thousand physicians use essential oils in their practices. Greatly supporting the skin, easily absorbed, essential oils can reach the organs to be treated through the connective and lymphatic tissues and the circulatory system. It wasn't until the 19th century that chemically produced medication began to replace essential oils as healing agents.