On the scent of medical aromatherapy – when and how can aromas influence the body?

There is a well-known saying that nature is the best medicine. One just needs to look at the whole host of plant-derived medicines to see that this adage holds true. But when it comes to the power of scents from essential oils, the idea has mostly been treated negligibly. Although there is growing interest in the field, the lack of quality studies surrounding its application both in laboratory and clinical settings have hampered the legitimisation in therapeutic practice. A recent study, published in the prestigious journal << Human Psychopharmacology: Clinical and Experimental >>, seeks to change this perception and ensure that the wisdom above can be applied to scents, too (Schneider et al. 2018).

Progress has been made in aromatherapy research but methodological flaws, lack of standardisation, poor assessment protocols and failure to determine the correct mode of administration continue to hamper study results (Shin et al. 2016, Schneider et al. 2018). What has not helped either, is the fact aromatherapy has become the generic term used to describe the use of essential oils on the skin, for massage, or in the ambient air. In France, it is even used for oils consumed orally under medical supervision. It is no surprise this conceptual ambiguity has hampered the advancement and acceptance of essential oil research. To help with the advancement of aromatherapy, the definition needs to be narrowed down. Oral and topical administration should more correctly be known as phytotherapy, while in contrast, it is the inhalation of volatile compounds that constitutes aromatherapy (Tisserand and Young 2014). However, there is more to aromatherapy than merely smelling aromas. An even more precise definition emphasises the functional aspect of scent application; that is, the use of odour molecules to specifically provoke a psychological or physiological response (Buchbauer, et al. 1993) and in this context, both the delivery method and the physiology of the nose needs to be considered.

Why should we use aroma inhalation?

Our sense of smell has a direct input to the brain, triggering a response in the hippocampus, amygdala and the hypothalamus, structures responsible for mood, emotion and homeostasis. This means our sense of smell can play a large role in influencing our autonomous nervous system (Merrick et al. 2014) and does not need to enter the blood stream in order to do so. Smell has another added benefit in that unlike other senses, it bypasses the thalamus, allowing for extremely rapid signal processing. In fact, odour transmission speeds to the brain occur in 150-200ms (Khan and Sobel 2004, Olofsson 2014). This is far quicker than oral administration which takes approximately 30 minutes for an active substance to reach its target and transdermal application which ranges from minutes to hours (if at all). This makes inhalation perfect when quick action is needed. When corr