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 correctly accounted for, the extremely complex sense of smell can be used to bring about drastic physical change, far quicker than virtually any other method and it does so in a non-invasive manner.

How is this achieved?

Just like you would place an ice-pack on an injury rather than sitting next to it, the same goes for scents. Relying on the release of volatile scent molecules via dispensers into ambient air to elicit responses is unlikely to produce any meaningful results, particularly in a therapeutic context, and it is no wonder most studies fail to show the benefits of aroma inhalation. For scents to be effective, they need to be delivered directly to the target location: the olfactory receptors. And this can only be done using an inhaler. In fact, intranasal delivery of aromas has been shown to influence parameters such as blood pressure, blood oxygen levels, cortisol, cognitive function and even pain dynamics among others (Schneider et al. 2018).

When working with scents in the form of aromatherapy, there are three vital factors that need to be considered:

1. The first is that olfactory responses are highly dependent on the concentration of odour molecules that reach the nose. The higher the concentration, the greater the number and type of receptors that are stimulated, and thus the larger the response (Buchbauer et al, 1993, Laing et al, 2003; Purves et al, 2001). Only about 5-10% of the air we breathe normally reaches the olfactory epithelium in the nose, the region where “smell” (Delank, 2008, Keyhani et al, 1995). This means that any scent released into ambient air is not only heavily diluted but would never reach the nose in any meaningful therapeutic quantity in the first place. By delivering scents with an inhaler, the air that reaches the olfactory system even with regular breathing is completely saturated, resulting in an intake of scent molecules at a level high enough to elicit a physiological and psychological effect.

2. The second is habituation. Habituation is the decreased responsiveness to an odour stimulus (and thus effectiveness) and is brought upon by sustained exposure to a scent. Contrary to what might be expected, the longer one is exposed to a scent, the less effective a scent is. Additionally, the weaker the aroma, the quicker the onset of habituation (Chaudhury 2010, Dalton and Wysocki 1996). This means that any method of aromatherapy where one is constantly exposed to aromas will rapidly result in olfactory habituation, greatly reducing the efficacy of that treatment. Instead, aromas must be delivered in brief, intense bursts in order to produce the largest effects.

3. The third is the sniff. The sniff is the biological mechanism for bringing ambient air into contact with the olfactory receptors in quantities beyond that of regular breathing. It is what we use to “smell” and naturally plays a role in any treatment using aromas (Schoenfeld and Cleland 2006). The sniff is more than just a simple delivery method however, as it is vital for our olfactory perception, which in turn is vital for aromatherapeutic effect. Researchers have found that mechanical stimulation (the information from the airflow) caused by the sniff works in parallel with the chemical stimulation (the binding of the molecules to the olfactory receptors) to improve how we smell. It is thought that mechanosensitivity may actually increase the sensitivity of our nose, which in turn benefits any treatment that utilises it. Thus, the sniff should be utilised to enhance the efficacy of any treatment involving odour inhalation. ((Laing et al. 2003, Kepecs et al. 2006; Mainland and Sobel 2006; Scott 2006, Verhagen et al. 2007).

These three factors are so important that a study, part of a series of five, published in the Journal <<Stress and Health>> showed that the direct stimulation of the olfactory receptors using an inhaler (AromaStick®) was up to three times more effective at reducing stress-related biomarkers (systolic and diastolic blood pressure and heart rate large) than that same aroma used as a room spray. In fact, subjective wellbeing aside, the physiological effects of the room spray were on par with that of passive resting, clearly suggesting the limited clinical benefit. The inhaler additionally outperformed other well established, widely used methods of relaxation such as progressive muscle relaxation and homeopathic treatments and showed, in another study, a large impact on the body’s hormonal regulation by reducing the release of salivary cortisol by up to 17%. All that was needed was three inhalations from the inhaler over a period of 10 minutes for such effects to occur (Schneider 2016a).

The use of an inhaler does not just benefit those attempting to influence stress biomarkers, however; and several studies utilising the AromaStick inhaler, involving nearly 500 individuals across them, showed that a whole host of psychological and physiological parameters can be affected. In fact, one study showed that direct application of odour can drastically influence pain dynamics (both menstrual pain and chronic back pain) when used alongside conventional pain treatment, improving the time until onset of pain relief, duration of pain and pain intensity by as much as 30% above the standalone pain treatment (Schneider 2017). Another study showed intranasally delivered odours can heighten cognitive function by up to 29% (Schneider 2016b) while a further study showed that scents can influence arterial blood oxygen levels. In fact, the use of an inhaler increased the blood oxygen levels above that of normal deep breathing by a factor of 2.5 and provided elevated levels three times longer. This study showed another surprising result: heightened arterial blood oxygen levels were measurable within 5 seconds of sniffing an odour inhaler, once again highlighting the speed with which inhalation produces an effect (Schneider 2017). Seasonal allergic rhinitis (hayfever) and weight loss were also conditions that were successfully influenced through the use of an inhaler (Schneider 2019, Singer and Schneider 2017). In fact, the reactions caused by the inhalers across all studies fell within an unusually high effect range which is seldom observed in scientific studies. It should be noted that these effects are not durable over hours. The benefit of this method is short term, and thus these methods, particularly in clinical settings, should be viewed not as a replacement to medication, but as a complement. The fast action and the powerful effects can provide much needed support in the moment it is needed.

It should be noted that the primary reason the studies were conducted was in order to investigate whether an inhaler (and the blends) produced an effect or not. This means that, much like with other studies on the topic, the mechanism behind the results was not investigated. To ensure accurate and unbiased results, however; these studies followed strict scientific protocol. They were randomised, double-blinded and where possible, placebo controlled. For aromatherapy to gain wider clinical and scientific acceptance, this aspect is vital. Additionally, the mode of application was explicitly defined, and any study on aromatherapy that is conducted needs to ensure that this point is clear. Conceptual ambiguity must be avoided in order to advance the field. The second reason for these studies was to show that it is in fact possible to utilise a standardised tool in order to investigate the efficacy of an aromatherapy treatment across various boundary conditions.

While it is true that very few molecules are needed in order to be smelled (Bhandawat et al, 2010), it is not true that very few molecules are sufficient for a scent to be therapeutically relevant. What these studies show is the fundamental importance of playing to the sense of smell’s strength; (1) Olfactory responses increase along with the molecular concentration (2) Limited exposure time produces the greatest effects; and (3) utilisation of the sniff delivers odour molecules to the necessary receptors and supports odour perception. By not taking these three factors into account, using aromas is hardly more than setting a pleasant ambience. When the physiology of the nose is taken into account, however and when aromas are delivered appropriately, the sense of smell is an incredibly powerful tool that can drastically influence a large number of physiological parameters. Not only is this important from a practical point of view but is important in opening the door for this method’s use in both wider research and eventually in clinical practice. It should also be said, however, that despite these visible effects, this application cannot and should not be used as a replacement for medication, but instead be used as a complementary component. On the other hand, the potential for this method is huge, and the research is only beginning to scratch the surface of what is possible with aroma inhalation.

Nick Singer, author of this article, will be speaking at the Complementary Health Professionals annual conference on the 26th October 2019 where you will have the opportunity to learn more about his company's research and sample their 100% organic AromaStick inhalers for yourself.

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