Medical aromatherapy revisited—Basic mechanisms, critique,
and a new development
RECON–Research and Consulting, Freiburg,
AromaStick AG, Sargans, Switzerland
Rainer Schneider, RECON–Research and
Consulting, Unterer Mühlenweg 38 B,
Freiburg 79114, Germany.
Objective: According to a series of recent meta‐analyses and systematic reviews,
aromatherapy has shown to be effective in treating patients with different medical
conditions. However, many of the clinical studies are of rather low methodological
quality. Moreover, there is much conceptual ambiguity with regard to what aroma-
therapy actually constitutes.
Method: In this paper, we discuss the conditions under which aromatherapy is most
likely to be of medical value by outlining the workings of the olfactory system and the
necessary requirements of odors to be therapeutic. We then introduce an aromather-
apeutic inhaler that was tested in a series of studies involving 465 participants.
Results: This inhaler (AromaStick®) produced large to very large effects across a
variety of physiological target systems (e.g., cardiovascular, endocrine, blood oxygen-
ation, and pain), both short term and long term.
Discussion: Inhalation of volatile compounds from essential oils yields almost
immediate, large, and clinically relevant effects as long as the scents are delivered
highly concentrated from an appropriate device. The changes caused in the body
seem side effect‐free and can be sustained when inhalation is repeated.
AromaStick®, aromatherapy, clinical effects, inhaler, olfactory system
Every ancient culture used scents either for hygienic or remedial pur-
poses. For example, Hippocrates (460–370 BC) introduced scents to
treat hysteria, which he regarded as symptoms caused by movements
of the womb (King, 1993). Records show that the therapeutic use of dis-
tilled oils was already applied in the 10th Century AD (Forbes, 1970).
According to estimations, there are about 350,000 plant species, among
which approximately 17,500 are aromatic plants (Tisserand & Young,
2014). Of these, some 400 are commercially processed for their aro-
matic raw materials. However, after the introduction of clinical efficacy
testing in the 1950s and the rise of pharmacotherapy dominating West-
ern medicine, aromatherapeutic approaches were almost exclusively
restricted to alternative medical approaches. Until recently, conven-
tional medicine regarded aromatherapy as pseudoscientific due to a lack
of compelling empirical evidence supporting its effectiveness. In the last
decade or so, this situation has changed, and there is growing medical
interest in aromatherapy. Clinical studies as well as meta‐analyses show
that some of the former reservations against the medical use of essen-
tial oils can no longer be upheld.
There is no doubt that essential oils have very specific pharmaco-
logic properties, which may be actively used to elicit specific physiolog-
ical responses (Edris, 2007; Hongratanaworakit, 2004). For example,
certain odors (e.g., peppermint oil) may alter the endogenous opioid
pathways of the brain and therefore reduce pain or anxiety (Bushnell,
Ceko, & Low, 2013; Ching, 1999; Villemure, Slotnick, & Bushnell,
2003). Other odors (e.g., eucalyptus or thyme) have remarkable antibac-
terial, antifungal, anti‐inflammatory, immunomodulatory, or antioxidant
effects (Brochot, Guilbot, Haddioui, & Roques, 2017; Caceres et al.,
2017; Divband, Shokr, & Khosravi, 2017; Hans, Grover, Deswal, &
Agarwal, 2016; Jaradat, Adwan, K'aibni, Shraim, & Zaid, 2016; Kenia,
Hoghton, & Beardsmore, 2008; Schönknecht, Krauss, Jambor, & Fal,
Received: 25 July 2018 Revised: 4 October 2018 Accepted: 16 October 2018
Hum Psychopharmacol Clin Exp. 2018;e2683.
© 2018 John Wiley & Sons, Ltd.wileyonlinelibrary.com/journal/hup 1of10
2016; Zhou et al., 2016). Recent meta‐analyses and systematic reviews
support the notion that aromatherapy may exert clinical symptom relief
when compared with placebo or standard treatment. For example, in a
meta‐analysis examining different types of pain management, aroma-
therapy was superior to placebo in treating postoperative, obstetrical,
and gynecological pain (Lakhan, Shaefer, & Tepper, 2016). A systematic
review investigating the effects of aromatherapy on dysmenorrhea
showed that the alleviating effect on menstrual pain was larger with aro-
matherapeutic interventions than with placebo interventions (Song,
Lee, Min, Fike, & Hur, 2018). In a meta‐analysis of randomized con-
trolled trials on stress reduction, aroma inhalation yielded favorable
effects compared with no treatment, but this effect mainly showed in
subjective self‐reports (Hur, Song, Lee, & Lee, 2014). An evaluation of
aromatherapy on sleep quality including randomized controlled trials
and quasi‐experimental trials revealed that it was effective in both
healthy and unhealthy individuals, especially when used as inhalation
rather than massage therapy (Hwang & Shin, 2015). By contrast, a
systematic review investigating aromatherapy for treating depressive
symptoms found stronger relieving effects for massage aromatherapy
than for inhalation aromatherapy (Sánchez‐Vidaña et al., 2017).
Together, these findings demonstrate that therapeutic use of
essential oils may exert clinical effects. In general, aromatherapy may
be applied for a variety of medical conditions, but it appears to be most
effective for medical conditions whose underlying mechanisms involve
emotional and attentional information processing (Villemure et al.,
2003), as well as the activity of the autonomous nervous system (Haze,
Sakai, & Gozu, 2002).
Unfortunately, many of the clinical studies are of rather low
methodological quality. For example, a systematic review of cancer
patients found some effects of aromatherapy massage for long‐term
pain, anxiety, and quality of life but concluded that these did not
translate into clinical benefit due to the low quality of the studies
(Shin et al., 2016). In the above cited analyses, up to 50% of the
screened studies were reported to be of insufficient quality regard-
ing the key outcomes, the mode of administration, or the assess-
ment protocols. There are additional reasons that may either
benefit or harm the evaluation of aromatherapeutic interventions.
One critical factor pertains to the lack of accuracy of what aroma-
therapy constitutes. Most importantly, there is much confusion
regarding the definition of aromatherapy. Working with essential oils
per se is not sufficient to make a clinical claim. In the medical con-
text, applying them topically or even internally is actually
phytotherapy. In contrast, working with volatile compounds of
essential oils by inhalation is aromatherapy (Tisserand & Young,
2014). This mix‐up and conceptual ambiguity even in high‐ranked
research papers exacerbates any objective assessment of the clinical
use of essential oils. Many researchers seem at a loss or partially
ignorant when testing the specific factors constituting an alleged
aromatherapy. Unfortunately, this problem also pertains to studies
investigating cellular mechanisms of essential oils. For example, in a
study reviewing the evidence from the scientific literature regarding
the underlying mechanisms of limonene for treating different dis-
eases, the authors mistook consumption with inhalation and draw
conclusions which at best should be regarded as ambiguous with
regard to the functional pathways involved (Vieira, Beserra, Souza,
Totti, & Rozza, 2018). Likewise, in a study discussing the phyto-
chemical mechanisms of aromatherapeutic oils for the treatment of
behavioral and psychological symptoms in patients suffering from
dementia, the authors call for more rigorous research. However, this
conclusion is made without providing a sound definition of what
constitutes aromatherapy (Scuteri et al., 2017). Finally, in a recent
systematic review and meta‐analysis exploring the effects of aroma-
therapy on the treatment of psychological symptoms in postmeno-
pausal women (Babakhanian et al., 2018), the authors are caught in
the conceptual trap that has made aromatherapy a somewhat dubi-
ous intervention by confusing the very functional mechanisms they
wish to investigate. When concluding that aromatherapy massage
improves psychological symptoms, no differentiation is made
whether the causative mechanism is the physical therapy (likely) or
the aromatherapy (unlikely), thus adding to the confusion whether
aromatherapy has clinical benefits.
From this, it becomes clear that the current knowledge of the
effectiveness of essential oils in the clinical context is insufficient.
Moreover, much of what passes today for aromatherapy is nothing
else but setting and ambience, which at best may be regarded as
an unspecific factor. Before we elaborate on this, we will briefly
outline the olfactory system to demonstrate how, why, and when
aromatherapy is beneficial.
2|THE PHYSIOLOGY OF THE OLFACTORY
Unlike other sensory systems, scientific interest in the olfactory system
has long been marginal and only recently received greater interest. This
was overdue because, as mentioned above, the importance of the sense
of smell is crucial for human phylogeny.
1. Olfactory receptor genes make up 3% of all genes, rendering
them the largest gene family in the human genome (Boron &
2. The body contains tens of millions of olfactory receptor cells
which can be found in almost every organ, including the skin,
the brain, the heart, and the gastrointestinal tract.
3. Not only is olfaction the oldest sense, and therefore probably the
most meaningful for survival, it is also the only one that is not
subjected to neuropsychological filtering processes: Olfactory
stimuli are registered in the rhinencephalon, which directly relays
sensory information to the amygdala without projecting to the
thalamus (Masaoka & Homma, 2011).
4. The direct link to the brain operates at a transmission speed of
about 200 ms and exceeds that of most other physiological senses
(Khan & Sobel, 2004), and one single molecule suffices to trigger an
action potential on the receptor site (Su, Menuz, & Carlson, 2009).
5. In the nasal cavity, we find not only the olfactory system but also
the trigeminal system. Most odorant molecules stimulate both
systems simultaneously, which has consequences for the percep-
tion of odors and the somatosensory innervations associated with
them (Brand, 2006).
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6. Contrary to the estimate of about 30,000 scents, humans are
claimed to be capable of distinguishing at least one trillion
different scents (Bushdid, Magnasco, Vosshall, & Keller,
2014), although this estimate has recently been questioned
(Gerkin & Castro, 2015; Meister, 2015). Whatever the exact
number of scent discrimination may be, it is obvious that
the human olfactory system is quite remarkable and biologi-
cally of great importance. This is also illustrated by the fact
that a large variety of olfactory receptor neurons found in
the nose are organized in quite a complex way. This neuronal
network contains an enormous variety of receptor proteins (G
protein‐coupled receptors), which are encoded by a total of
over 350 genes (Fleischer, Breer, & Strotmann, 2009; Gerkin
& Castro, 2015).
Obviously, human olfaction is anything but an inferior sensory organ
even when compared with color vision, which is generally regarded as
the most advanced human sensory organ. For many scents, the thresh-
old of detection is in the parts‐per‐billion range (Devos, Patte, Roualt,
Laffort, & Gemert, 1990). This accuracy of detection has been found
to afford humans the ability to differentiate scents that vary only in
one molecular component (Laska, Ayabe‐Kanamura, Hubener, & Saito,
2000; Laska & Hubener, 2001; Laska & Teubner, 1999). The level of
complexity of the olfactory system is also reflected in the way smells
shape our experiences. Neurobiological research has shown that smell
experience is mediated by higher order (prefrontal) processes
(Gottfried, 2006). When odor molecules hit the nasal mucosa, first‐
order neurons conduct the odor‐elicited response to the olfactory bulb.
The olfactory tract, a complex structure of olfactory sensory axons join-
ing with second‐order dendrites (mitral and tufted cells) located in the
olfactory sulcus of the basal forebrain, transmits the information to
numerous areas within the frontal and dorsomedial lobe. Collectively,
these projections make up the primary olfactory cortex. Higher order
projections from each of these olfactory structures converge on the
orbital prefrontal cortex, the amygdala, the hypothalamus, the basal
ganglia, and the hippocampus (Haberly, 1998; Masaoka & Homma,
2011; Price, 1990). This complex of intertwined neuronal systems
causes odors to act on the neuroendocrine system, neurotransmitters,
and neuromodulators of various brain centers and is responsible for
the modulation of perception, cognition, and behavior (Kiecolt‐Glaser
at al., 2009).
Taken together, and in addition to the obvious unspecific effect of
aromatherapeutic odors (e.g., their pleasantness), the very physiology of
olfaction is the reason why essential oils lend themselves as specific
therapeutic agents. However, for aromatherapy to be effective, it must
fulfill certain criteria over and above what the highly sensitive physio-
logical capacities of olfaction can detect.
MISCONCEPTIONS AND IMPORTANT
The term ‘aromatherapy’is rife with misconceptions, even within
the realm of biochemistry (Singer & Schneider, 2016). It is
commonly used as a generic term to describe the use of essential
oils on the skin, for massage, or in the ambient air. An even more
vague definition includes the use of essential oils added to cos-
metic care products. In some countries (e.g., France), aromatherapy
even includes the intake of essentials oils, making the whole con-
cept more ambiguous. It is important to note, however, that nei-
ther the involvement of an odor nor a treatment is sufficient for
the claim that an application is aromatherapeutic. A precise and
narrow definition of the term defines aromatherapy as the use of
scents for the purpose of provoking psychological or physiological
responses. The crucial element of aromatherapy, therefore, is the
functional aspect of the used scents (Buchbauer, Jirovetz, Jager,
Plank, & Dietrich, 1993). Furthermore, any effect elicited by a
the method of application, which imperatively addresses the con-
cept of molecule concentration reaching the target system. In the
case of inhaled scents, air saturation is a very important factor
for eliciting the response. However, this relationship is not linear
such that prolonged maximum air saturation ensures maximum
effects. Due to the laws of habituation the body's perception of
sensory stimuli is regulated in a way as to ensure negative
feedback between stimulus intensity and the response intensity.
Sustained exposure to a specific odor stimulus inevitably results
in the intensity of the stimulus being perceived as reduced. This
physiological phenomenon has an important biological function, as
it allows one to remain receptive to new stimuli. On the other
hand, the intensity of the response is dependent upon the degree
of neurological processing, with direct sensory processing linked
to a stronger response.
Our ability to detect relatively low levels of scent does not contra-
dict the fact that potential volatility of a scent is unimportant. To the
contrary, to ensure a full effect, scents must be delivered directly and
at maximum concentrations to the nose. This is one of the reasons
why the empirical evidence testing aromatherapeutic interventions is
noticeably varied and heterogeneous. Apart from experimental
research testing specific properties of the olfactory system even below
the threshold of perceptibility by highly standardized apparel such as
face masks (Masaoka et al., 2013), the effects of odors are usually
tested in an environment that allows generalizability of the results to
natural and clinically realistic environments (e.g., the therapeutic con-
text). Depending on the mode of application, there may be major ther-
apeutic differences even if effective scents are administered.
In addition to the technical aspect of odor administration, there
are a number of biochemical aspects that account for the effective-
ness of aromatherapy.
1. One very important factor is purity of the substance. Many
essential oils are diluted with cheap synthetic and semisynthetic
monoterpenes (Braun & Franz, 2001; Werner, 2005).
2. Another factor is the use of single note or complex blends.
Although most odors tested for aromatherapeutic purposes are
single note, the therapeutic benefit may be enhanced by using
complex scent compositions. This is because complex scent
blends act synergistically (Lis‐Balchin, Deans, & Hart, 1997), and
SCHNEIDER ET AL.3of10
many of the ailments treated are associated with different symp-
toms, which are more likely to be more adequately treated with
complex scent blends. This is also underscored by the principles
of phytotherapy that exploit the combined action of a mixture
of constituents in order to maximize the number of synergistic
or antagonistic interactions that may exist between different phy-
tochemicals (Efferth & Koch, 2011).
3. Although many aromatherapeutic agents are synthesized, there is
empirical evidence showing that the brain differentiates between
them. For example, a study measuring the brain activity of
women found that real body odor samples obtained from friends
and strangers were processed by different parts of the brain than
their synthetic odor mix counterparts (Lundström, Boyle, Zatorre,
& Jones‐Gotman, 2008). More importantly, natural scents may be
more effective due to their chirality. Synthetic (racemic)
substances always contain mirror molecules that may have
important pharmacokinetic differences (Szelenyi et al., 1998).
Furthermore, the majority of synthetic scents consist of only a
few molecules. Natural scents, on the other hand, are complex
mixtures of up to several hundred individual substances—which
explains why the overall effect of such complex scents is only
rarely limited to the actions of just one or some of their
components. Natural scents are preferable to synthetic ones for
yet another reason. Due to manufacturing processes, many
synthetic scents contain traces of contaminants or additives that
may be potentially harmful.
4. Unlike pharmacologic agents, natural plant‐derived raw mate-
rials are difficult to standardize because of factors that are
difficult to control (e.g., population‐specific taxons, climate,
and chemotype variations). Biologically speaking, natural
plants will produce varying levels of different essential oils
to protect themselves from potential pathogens and
therefore sources of raw material will always vary. It may
therefore not be ruled out completely that depending on
the source of the scents slightly different therapeutic
outcomes may ensue.
We may therefore formulate the basic preconditions for an effective
aromatherapy as follows: It must (a) involve volatile compounds of
essential oils by inhalation, (b) directly and specifically target the nose,
(c) in high enough molecule concentrations that are able to trigger
physiological changes. In a broader sense, effective aromatherapy
must (d) involve natural essential oil compounds of high
phytochemical quality, and (e) be potent enough to strongly stimulate
the olfactory system without causing habituation.
4|NEW DEVELOPMENTS: THE
Recently, a lipstick‐sized nasal inhaler has been developed that
delivers scents concentrated and unadulterated to the nose forcing
the person to sniff for information acquisition. The sniff is the
mode of action that carries messages from the environment into
the olfactory system for processing (Sobel et al., 1998). In resting
breathing, this is to a far lesser degree the case because only a
fraction of inspired air encounters the olfactory epithelium, that
is, approximately 5–10% (Keyhani, Scherer, & Mozell, 1995). Fur-
thermore, the neurons in the nose are sensitive to air pressure
and this mechanosensitivity is thought to increase the sensitivity
of the nose (Mainland & Sobel, 2006; Scott, 2006; Verhagen,
Wesson, Netoff, White, & Wachowiak, 2007). Thus, the
AromaStick® guarantees full absorption of the scent molecules
when put close to one nostril (with the other one closed with a
finger) during inhalation and then repeated with the other nostril.
Unlike similar devices, the inhaler consists of a wet filter held
centrally, almost floating, inside the tube. This allows for the active
ingredients to avoid contact with the container, which in turn
guarantees a smooth flow of air around the filter. The centrally
suspended filter has an additional benefit as it avoids direct con-
tact with the PP material of the primary container, thus minimizing
the risk of a chemical reaction between essential oil and material,
which potentially could result in undesired vapors. Depending on
the purpose of the inhaler, it contains different complex scent
compositions of 100% natural essential oil ingredients. The inhaler
is designed and fabricated by AromaStick Inc., Sargans, Switzerland.
Quality control is done by an independent laboratory. The essential
oils are purchased from reputable suppliers complete with
certificates of analysis. Freshness of the oils in the finished product
is guaranteed by a foil‐sealed container. The odor has shown to
maintain freshness for at least 24 months according to several
stability tests under GLP (good laboratory practice). Once opened,
an AromaStick® lasts approximately 6 months. Although not
strictly invented for medical purposes, the inhalers have shown to
produce large to very large effects across a variety of
physiological and psychological target variables.
Before we introduce the body of evidence for this new method of
working with scents, we will address a fundamental issue affecting
empirical science as a whole and the conclusions derived from clin-
ical testing in particular: null hypothesis significance testing (NHST).
NHST has become the standard for a broad range of clinical test-
ing. However, for more than 70 years, methodologists have warned
that the use of significance tests is in many cases not only statisti-
cally and logically wrong, but potentially detrimental to the
advancement of knowledge (for recent overviews, cf. Branch,
2014; Lambdin, 2012). In fact, contrary to the belief of most
researchers, there is no empirical evidence supporting the applica-
tion of NHST (Armstrong, 2007). Although major steps have been
undertaken in the last decades to improve the quality of clinical
research, for example, by issuing guidelines such as CONSORT
(Moher, Altman, Schulz, Simera, & Wager, 2014), it is surprising
that the fundamental problems of NHST are seldom addressed.
We will briefly discuss some of the fundamental problems of NHST
to illustrate how precarious and misleading the use of significance
tests is, whose use in psychology has been dubbed the “dirty little
4of10 SCHNEIDER ET AL.
1. Significant results do not tell anything about the relevance of the
underlying effect. Also, they are not comparable across different
studies. Many so called “highly significant”results are only of
small clinical importance when expressed in terms of the actual
size of the effects (Ioannidis, 2005; Lykken, 1968).
2. Any null hypothesis can easily be rejected with sufficiently large
or homogenous samples, and statistical tests can arbitrarily be
rendered significant regardless of the meaningfulness of the rela-
3. Many statistical assumptions associated with NHST are
misconceived (Hubbard, 2004; Hubbard & Armstrong, 2006;
Schmidt & Hunter, 1997; Thompson, 1999). One such fundamen-
tal error is the combination of Fisher's evidential statistic (pvalue)
and Neyman–Pearson's error estimate (α). Despite common
misconceptions, they are not in any meaningful way associated
when stating that p<α.
4. This causes the illogic that accompanies NHST: To believe that if
a set of data is unlikely to occur if the null hypothesis is assumed,
one can conclude that it is probably wrong. In other words, when
the probability of αis smaller than the criterion applied, chance is
deemed unlikely to have produced the result, or formally put: P
(Data|H0) →P(H0|Data). Yet both conditional probabilities are
unrelated and, in fact, distinct from each other and cannot be
reversed (Gigerenzer, Gaissmeyer, Kurz‐Milcke, Schwartz, &
Woloshin, 2008; Kalinowski, Fidler, & Cumming, 2008).
5. It is rather sobering that many statistical experts and academics
are not able to give a correct definition of a so called significant
result (Haller & Krauss, 2002; Thompson, 1999).
To circumvent these problems, methodologists advise to focus on
effect sizes and confidence intervals because they are far more indic-
ative of the importance of clinical results. Additionally, effect sizes are
directly comparable because they are standardized. Fortunately, more
and more scientific journals are open to this idea and editors especially
of novel journals start questioning the logic of NHST.
5|EMPIRICAL EVIDENCE FOR THE
In the following, the results of a series of different studies
involving a total of 465 participants are reported, which aimed at
testing the AromaStick®. As outlined in Table 1, the analyses were
solely based on the effect size d (Cohen, 2008) and their respective
confidence intervals (95%; Borenstein, Hedges, Higgins, &
Rothstein, 2009). An overview of the main percentage changes is
depicted in Figure 1.
As can be seen, theeffects observed were large to verylarge accord-
ing to the commonly proposed criteria (Cohen, 2008; Hattie, 2009). In
fact, given that the average effect size in most fields is estimated at
d< 0.8 (Sedlmeier & Gigerenzer, 1989), corresponding to a mean differ-
ence of less than a standard deviation, the observed effects are quite
remarkable. In accordance with the rule of thumb that a relevant effect
should be visible to the naked eye (Cohen, 1992; Edwards, Lindman, &
Savage, 1963), we may conclude that this mode of aromatherapy pro-
duces changes that are far from clinically meaningless. To the contrary,
they attest to the workings of the olfactory system outlined above and
the presumption madethat the mode of application and molecule satura-
tion of the inhaledair is indeed one of the deciding factors for aromather-
apy to be effective.
To put the observed effects in perspective,it is helpful to elaborate on
their meaning. For instance, with a Cohen's dof 1.5, 93% of the
AromaStick® users were above the mean of the control group. In
principle, thismeans that if 100 peoplego through the AromaStick®treat-
ment, 54.5 more people have a favorable outcome compared with receiv-
ing the control treatment. A dof 2.8 means that100% of the AromaStick®
treatment group was above the mean of the control group, and thereis a
98% chance that a person picked at random from thetreatment group had
a higher score than a person randomly chosen from the control group
(probability of superiority). If 100 people went through the inhaler treat-
ment, 77.5 more people would have a favorable outcome compared with
the control treatment. From these examples it becomes clear that treat-
ment with the AromaStick® benefitted a vast majority of its users.
One of the striking observations across the studies is the fact that
only a few inhalations sufficed to affect the target systems tested.
Equally interesting was the magnitude of the effects. For instance, the
reduction of systolic and diastolic blood pressure and heart rate
(Schneider, 2016a) proved that the inhalers effectively reduced the
activity of the sympathetic nervous system. In fact, they did so even to
an extent that was reminiscent of the effects of antihypertensive drugs.
That this also showed in individuals who were not under particular stress
(Study 4) points to the inhalers' general potency and is in alignment with
the fact that very stable and closely regulated systems like blood oxygen-
ation can even be “optimized”over and abovenormal physiological func-
tioning (Schneider, 2017a). In fact, the direct supply of odor molecules to
the nose not only increases the oxygenation effect of deep breathing by
a factor of 2.5 but also keeps it at a higher level three times longer.
Where tested, all participants reported improvement in mood and
well‐being. This was no doubt in part due to the odors' pleasantness but
mostly constituted a specific effect of the active profiles of the inhalers.
Research has shown that pleasant odors induce mood improvement
and decrease pain unpleasantness when pain intensity is attended to. In
contrast, paying attention to the intensity of odorous stimuli during pain
stimulation decreases pain intensity perception and pain‐evoked brain
activity (Villemure et al., 2003). Thus, the odor molecules delivered by
the AromaStick® inhalers may work in two different ways. In the pain
studies(Schneider, 2017b),the individuals suffered from chronic or recur-
rent pain. Chronic pain patients have shown to suffer extensive alter-
ations in the neurologic pain matrix (Apkarian et al., 2014; Baliki, Geha,
Fields, & Apkarian, 2010). Both activity and connections of important
pain‐processing brain regions may be (permanently) altered, which often
causes marked changes in behavior (e.g., increase in anxiety and/or
decrease in reward learning, dysfunctional coping with pain). These
patientsmay have a decreased threshold for pain signals, which enhances
physiological and psychological reactions associated with discrepant
bodily processes (Bendelow & Williams, 2008; Simons, Elman, & Borsook,
2014). They also tend to perceive pain relief or pain reductions as less
rewarding (Campbell & Edwards, 2009). Although parameters of pain
dynamics in these individuals are much more resistant and less variable,
SCHNEIDER ET AL.5of10
TABLE 1 Overview of main effects across different AromaStick® studies
Reference Type of study Sample Target variable ES/CI
Schneider, 2016a (Study 1)
Experimental Highly stressed individuals SBP 1.5
0.7 < d< 2.3
0.4 < d< 2.2
Schneider, 2016a (Study 2)
Experimental Highly stressed individuals SBP 2.5
1.5 < d< 3.4
0.4 < d< 1.7
0.4 < d< 1.7
0.1 < d< 1.6
Schneider, 2016a (Study 3)
Experimental Highly stressed individuals SBP 1.2
0.4 < d< 2.0
0.3 < d< 1.5
0.4 < d< 2.0
Schneider, 2016a (Study 4)
Experimental Healthy individuals SBP 2.3
1.5 < d< 3.1
1.6 < d< 3.2
1.2 < d< 2.7
Schneider, 2016a (Study 5)
Field Borderline hypertensives (responders) SBP 3.1
1.9 < d< 4.3
30 months every
2–3 hr daily
0.1 < d< 1.8
Schneider, 2016b Experimental Healthy individuals Concentration 1.3
0.5 < d< 2.2
+29% total cognitive performance
One inhalation before
each testing block
(eight total) ca. 10 min
Scanning speed 1.0
0.3 < d< 1.7
0.1 < d< 1.5
Schneider, 2017a Experimental Healthy individuals Blood oxygen saturation (SpO
1.5 < d< 2.5
3 breathing cycles
Schneider, 2017b (Study 1)
Field Women with menstrual pain Onset of pain relief 0.6
0.1 < d< 1.1
During menses for 1 hr
Pain duration 0.6
0.1 < d< 1.1
Schneider, 2017b (Study 2)
Field Chronic back pain individuals Pain intensity at relief onset 2.6
1.6 < d< 3.6
From strong to low
On pain days for 1 hr
Pain intensity after 3 hrs 3.7
2.4 < d< 5.0
From strong to very low
Schneider, in press Field Individuals suffering from Seasonal Rhinitis Overall nasal symptom relief 2.0
1.2 < d< 2.8
From moderate to little 14 days
a minimum of
eight times daily
Individual nasal symptom relief 2.8
1.9 < d< 3.7
From very much to moderate
Effect sizes/confidence intervals (rounded values).
Differences were calculated in comparison with baseline measures or controls depending of the type of study.
These studies explored different inhalers and different stress reduction interventions which are not reported here.
Aromatherapy given as adjuvant (add‐on).
6of10 SCHNEIDER ET AL.
the odor inhaler was nonetheless able to not only reduce pain intensity
but also to greatly improve time pain dynamics like pain duration.
Another observation was that the AromaStick® improved symptom
burden even in persons who had been suffering from the respective
medical conditionfor many years and who had been resorting to conven-
tional treatment for quite some time with moderate to little success. In
fact, most of them had come to terms with the fact they would live in
pain, have to be on medication to treat their blood pressure, continue
to suffer from seasonalrhinitis if not treated with antihistamines, or have
a hard time to find stress relief. As with every new treatment, one cannot
rule out that the effects observed may havebeen due to its novelty char-
acter. However, many participants had rather low expectancies that the
inhaler would bring them relief. Hence, psychological factors did not play
that much of a role (Schneider, 2012; Schneider & Kuhl, 2012) and, in
fact, could be totally discarded when accounted for (Schneider, 2017a,
2017b; Schneider, in press).
Together, these findings supportthe notion that, for aromatherapyto
be clinically effective, the act of smelling as such is as important as the
quality and specificity of the odor molecules absorbed. As mentioned
above, regular breathing only results in 5–10% of the inhaled air reaching
the olfactory epithelium in the nose. A special modeof sniffing is required
to direct airflow to the olfactory receptors at rates over and above that
rate if physiologically significant effects are to be caused by essential oils.
With the AromaStick® the primary focus for olfactory processing is
enhanced. As a consequence,the potentiallybeneficial effects of essential
oil components are potentiated causing distinct physiological changes.
There are a number of important inferences that can be drawn
from these findings.
1. The effects of the inhalers are specific and not due to unspecific
factors like expectation or pleasantness of the odors.
2. They target different physiological systems (blood oxygenation,
cardiovascular parameters, adrenal parameters, pain perception,
respiratory function, and brain faculties).
3. These effects are only produced when delivered directly to the
nose and not when diffused in the ambient air (which is the case
for almost all ordinary inhalation interventions). They are fast‐
acting and observable after only a few inhalations.
4. The inhalers outperform other interventions intended to alter
physiological processes (such as passive resting, progressive mus-
cle relaxation, placebo, or Bach flowers), enhance normal bodily
and cognitive functions (e.g., breathing and concentration), and
increase effective measures as adjuvant (e.g., pain).
5. They have very little to no side effects and are tolerated by nearly
6. The AromaStick® is suitable for self‐treatment, portable, and
therefore can be used anywhere and anytime.
7. Depending on the condition treated, users may vary in the degree
to which they respond to the inhalers. Obviously, as with any
pharmacologic agents, there are degrees of responsiveness due
to both the pharmacokinetics of odors (i.e., what the body does
to them) and their pharmacodynamics (i.e., what they do to the
body). Consequently, effects may be the highest in responders,
which was the case, for example, in Study 5 of Schneider
(2016a) and in the study by Schneider (in press).
Despite the findings of this new delivery method, there are a number
of unanswered questions that will be described briefly.
1. Due to the nature of the intervention, the exact dose of the inhaled
air cannot be standardized. This, however, applies to all inhalation
aromatherapies even when air diffusion is standardized. Designed
primarily for individual or personal application, users may need to
find the mode that delivers the best results. On the other hand, a
small person with a smaller lung volume will absorb fewer mole-
cules in one sniff than a larger person. Unlike for standardized
drugs (e.g., pain killers), the very act of sniffing is very idiosyncratic
and therefore physiologically adaptive.
FIGURE 1 Overview of some of the
physiological changes caused by different
AromaStick® inhalers; improvements are
depicted for the main effects reported in
Table 1. Cardiovascular parameters (blood
pressure and heart rate) were averaged for
Studies 1–4 in Schneider (2016a)
SCHNEIDER ET AL.7of10
2. The reported studies mainly investigated whether the inhalers
produce relevant specific effects. They did not investigate under-
lying mechanisms of how the effects were determined (e.g.,
neurobiologically and biochemically). Nonetheless, the effects
were noticeable for most users in those instances when there
was a relief of burden (e.g., stress or pain relief), and in that
regard, subjective experience is at least as important as objective
changes in medical parameters.
3. Some of the studies investigated symptomatology over an
extended period, but the jury is out as to how long the observed
effects actually last. In some medical conditions, the use of the
device may be prolonged as long as the burden exists (e.g., allergy
or hypertension). In some, it may be discontinued after the burden
has abated to a tolerable level (e.g., stress or pain).
4. Closely related to this point is the issue that therapy success can
only be achieved by applying the inhaler regularly and, in some
cases, many times a day. This is due to the fact that technically
only a limited amount of volatile scent molecules can be applied
per administration. In some field studies, participants decided
themselves to use the inhaler more often than required by the
study protocol. In turn, this also means that therapy success is
dependent on the user's discipline. Unlike drugs to be taken once
or twice a day and thus not requiring much diligence, the admin-
istration of the inhaler may be too cumbersome a treatment for
5. The degree to which the AromaStick® inhaler may lend itself as
an adjuvant should be addressed in more detail in future studies.
AromaStick® inhalers may not outperform pharmacologic agents
(e.g., pain killers), but they may assist in complementing them
such that the overall treatment effect is enhanced. This could
potentially even reduce the amount of pharmacologic intake, thus
reducing their side effects.
6. Likewise, there might be differences with regard to acute and
chronic ailments. It would be desirable to test the odor inhaler
against additional forms of active treatment in clinical settings
with different boundary conditions.
7. The findings were not derived from a clinical setting or a medical
context, and therefore, the results may be biased. However, the
fact that the effects were large and replicable across a broad class
of conditions shows that the inhalers work.
7|SUMMARY AND DISCUSSION
The herein reported findings across a wide range of physiological sys-
tems show that the inhalation of volatile compounds from essential
oils yields almost immediate, large, and clinically relevant effects as
long as the scents are delivered highly concentrated from an appropri-
ate device. When sniffed in this manner, the volatile compounds of
essential oils have true aromatherapeutic capacities in the sense of
specific agents. Also, this form of application is noninvasive and less
likely to be corrupted by sensory habituation. The changes caused in
the body seem side effect‐free and can be sustained when inhalation
is repeated. Although unspecific effects like odor pleasantness may
contribute to the inhalers' overall effect, in the sense that they
enhance adherence, they are of only secondary importance. The
AromaStick® is potentially suited as a stand‐alone measure to address
everyday challenges or as an adjunct to medical treatments. The
presented studies call for replication and further studies.
All authors have contributed substantially to this work. R. S. designed
and conducted the original AromaStick® studies and wrote the man-
uscript. N. S. and T. S. studied the essential oils and the olfactory
system, developed the AromaStick® idea, composed the odor mix-
tures, and helped outline the manuscript with arguments beyond
the actual research.
CONFLICT OF INTEREST
The studies reported were funded by the company manufacturing the
inhaler (AromaStick®), and therefore, in principal, the principal investi-
gator R. S. could have been biased with regard to the outcomes. To
make sure that this was not the case, R. S. did not interfere with the
actual treatments and had no contact with the participants. Instead,
independent and, depending on the type of study, blinded experi-
menters ran the studies. Also, all collected data were initially blinded
as to the group allocations and only unblinded after the analyses were
performed. Last, the study was run under the recorded stipulation that
they be published independent of the outcome.
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ical aromatherapy revisited—Basic mechanisms, critique, and a
new development. Hum Psychopharmacol Clin Exp. 2018;
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