Introduction

Smell is the most mysterious and evocative of our senses: it is our chemical sense, informing us about the surrounding environment and giving information that is not tangible, visible or audible. This chapter explores the connections between a person’s thoughts, feelings and immune status, and suggests that the ability of essential oils to affect all these via the sense of smell makes aromatherapy a truly holistic therapy.

The impact of the mind and emotions on the body

Throughout the ages people concerned with healing have been aware that there is a connection between thoughts, emotions and the state of health of the physical body. The British Medical Journal in 1884 observed that ‘the depression of the spirits at these melancholy occasions (funerals) … disposes them to some of the worst effects of the chills’ (Wood 1990a). These effects can be real, and changes in blood chemistry have been recorded even when the emotions are conjured up artificially, as in the case of superstition. Three thousand years ago the impact and influence of the intangible human mind on the material body was recorded in the Old Testament: ‘A merry heart doeth good like a medicine; but a broken spirit drieth the bones’ (Proverbs 17: 22, King James version).

In modern times this has been recognized not only by psychotherapists and those in psychosomatic medicine, but also in general medicine.

Psychoneuroimmunology (PNI)

In the past the psyche, the nervous system and the immune system were studied more or less as independent systems functioning alongside each other, but without direct connections. The science of PNI attempts to understand how the brain and the immune system communicate with each other,

PNI is also referred to as psychoendoneuroimmunology (PENI).

The immune system

Neuropeptide messengers produced by the immune system, brain and nerve cells provide two-way communication between the emotional brain and bodily systems via hormonal feedback loops. The limbic system (hypothalamus and pituitary), the spleen, the adrenal and thymus glands all have nerve interconnections. Thus emotions are capable not only of directing the body but also of receiving and being modified by information feedback from cells in the body.

Adrenalin and cortisol are two of the many chemical messengers whose release can be triggered by negative emotion in sudden or long-term stress: these two hormones influence the immune system directly to switch it off (Borysenko 1988 p. 14). Adrenocorticotrophic hormone (ACTH) suppresses pituitary action by stimulating the adrenal gland to produce adrenaline (epinephrine), which is a stimulator of the autonomic nervous system (ANS). The idea has gradually gained ground that emotional states can translate into altered responses in the immune system: negative thoughts and sad emotions can sometimes temporarily lessen the effectiveness of the immune system. Hence the body puts non-material thoughts and emotions into physical effect, either to produce a beneficial healing effect or to inflict self-damage. This idea is echoed by many writers.

The effect of the emotions on health

It has not yet been possible for anyone to show a link between a particular emotion and any specific physical disease – ‘Pessimism is not linked to any particular disease’ (Wood 1990b) – although pessimism or depression amplify symptoms of pain. It can probably be said that the course of nearly all disease is affected by thoughts, feelings, emotions and attitudes, which are in turn influenced by personality.

Thinking and healing

Using the mind to control pulse rate and breathing, and to bring about general relaxation of the body, has long been practised in different cultures. In the meditative state the brain waves drop from the β rhythm to the slower α rhythm; the blood circulation is diverted more to the brain and vital organs, with less going to the muscles, so that the heart rate is slower, blood pressure is lower and little oxygen is used.

All this is initiated by thought alone, effected via the hypothalamus. Hesse, experimenting on cats in the 1950s, found that when the hypothalamus was stimulated, increased activity or relaxation was produced (Hesse & Akerl 1955). Sometimes, in people suffering a terminal illness, this mind-to-body effect can make healing possible even though a cure is not.

It is now realized that for optimum healing the sufferer must be fully involved in all stages of the treatment, from diagnosis to final cure, and that all true healing comes from within. Healing is accomplished by mental and physical routes, with primary roles played by the patient, doctor and nurse, while family and friends take secondary supportive parts. As Plato wrote in the third century BC:

Trust and placebo

Another well-known example of the effect of thought on the physical body is the placebo effect. This happens when the cure or amelioration of an illness is due to the patient’s trust and belief in a prescribed substance, to faith in the healer, or frequently a combination of both. Dummy painkillers are 56% as effective as morphine in the treatment of severe chronic pain (Chaitow 1991). This remarkable and much-used placebo effect is important in all healing: when people are made to feel better, positive healing thoughts, which encourage the healing process, are generated. If an aromatherapy treatment does no more than make people feel better in themselves, it puts the whole person into healing mode.

‘Immunity is to some degree under mental control’ (Wood 1990a). Just as positive healing thoughts induce healing reactions in the body, the efficiency of the immune system is reduced by negative beliefs and thoughts. Immunity from disease appears to be enhanced or diminished by beliefs, and by the environment in so far as it affects our emotions. Fortunately, the human race is intrinsically optimistic, with a will to survive.

Where does aromatherapy fit in?

How can aromatherapy play an effective and worthwhile part in the mental–physical sphere of healing? It is established beyond doubt that essential oils can have physical impact in that they are bactericidal, anti-inflammatory, antifungal, appetite stimulating, hyperaemic, expectorant etc. (see Ch. 4 and Table 7.1). They possess properties which can affect the mind and emotions to sedate, calm and uplift; they also have effects on bodily systems, they evoke memories, change perception, calm agitation, relieve stress, activate cognitive responses and affect intercommunication (Cook 2008, Ouldred & Bryant 2008). They are therefore ideal tools for tackling not only physical problems but at the same time mental and emotional states, working via the sense of smell.

Table 7.1 Effects of essential oils used internally and externally (from Schilcher 1984)

The placebo effect (expectations effect) is another factor that may influence the effect of an aroma on human behaviour, mood and health:

Relaxation response

When safe and calm, people experience the opposite of the stress response, in that tension, blood pressure, oxygen use and so on are reduced. This has been termed the ‘relaxation response’ (Benson 1975). It can be brought about by many means, including reading, listening to favourite music, contemplating nature – and aromatherapy.

When, during a massage, the touch of the therapist is combined with the mental and physical effects of the essential oils, the client is helped to achieve a temporary separation from worldly worries, somewhat akin to a meditative state. The massage itself induces the relaxation response, which activates the body’s healing mode, and this, in conjunction with the essential oils, is outstanding for the relief of tension and anxiety, both physical and mental.

Whatever the method of application, the authors feel that in many cases most of the healing effect of essential oils is primarily through inhalation (see Ch. 6) via the mind and emotional pathways, and that a lesser part takes place via the physical body. There is no doubt that smelling plant volatile oils can affect the mood and general feeling of wellbeing in the individual. This is especially true when the essential oils are applied with whole-body massage: the physical and mental relaxation achieved during a massage session has to be experienced to be appreciated. To select essential oils to address the mental, emotional and physical needs of the client, the cause(s) of the health

problem must be identified. All essential oils have an effect on both mind and body, although much research needs to be done in this respect.

Pregnancy and children

The influence of odours on humans begins even before birth; the odour of anise was presented to 24 neonates and it was shown that babies born to mothers who consumed anise during their pregnancy showed a stable preference for the smell, whereas babies born to non-anise consuming mothers showed aversive or neutral responses (Schaal et al. 2000).

A report by Nordin et al. (2004) showed that abnormal taste and smell was reported by 76% of 187 pregnant women tested, typically believed to be caused by their pregnancy. Increased smell sensitivity was common during the early stages of pregnancy (67%), occasionally accompanied by qualitative smell distortions (17%) and phantom smells (14%). Smell abnormalities occurred less in later periods of pregnancy and were virtually absent after delivery. Abnormal taste sensitivity was fairly commonly reported (26%), often described as an increase in bitter and a decrease in salt taste. Pregnancy smell and taste disorders relate to fetal protection mechanisms to avoid poisons and increase salt levels for the expanded fluid levels.

Anecdotal evidence indicates that during pregnancy olfactory sensitivity is increased, and the lack of scientific evidence to back this up was investigated (Cameron 2007). One hundred women who did not smoke were tested and the overall conclusion was that the effect of pregnancy was small and inconsistent, but interestingly the women felt that they had heightened awareness of smells during their pregnancy.

Adding the aroma of lemon to a classroom helps to involve all the senses in the learning experience, and Chu (2008) says that low-achieving school-children experienced success in a written task in the presence of an ambient odour (herbal tea), and when they experienced this same odour in a later task they were shown to be significantly better than a relevant control group. Chu claims that this is the first study to show a classic conditioning effect to influence human behaviour (but see Aromas, Memory and Mood, below).

The sense of smell is important in children with severe learning difficulties (see Ch. 13) who may have diminished hearing and sight, and essential oils can be used to make their life easier and more friendly. Fragrances have been used on wristbands to identify carers, each with their own aroma, to identify the child’s possessions and to locate areas, rooms and facilities (Sanderson, Harrison & Price 1991). This technique can also be used to make a baby sitter acceptable to the child.

The elderly

Aromas are well accepted in homes for the elderly, where they can create a pleasant atmosphere, either stimulating or relaxing, and some aromas may create an ambience which will bring back memories, possibly sparking off nostalgic conversation between the residents, with obvious benefits (see Ch. 14).

Gender differences

There appears to be a gender difference in the impact on the mind of inhaled essential oils, as it seems that women are the more likely to derive beneficial results. One study indicating this was the use of Citrus sinensis [sweet orange] diffused into the waiting room of a dental practice, where the results of a questionnaire filled in by patients of both genders showed that sweet orange oil had a relaxant effect compared to non-odour controls. Compared to men, women had a lower anxiety state, a more positive mood and higher level of calmness. The typical smell of dental premises, eugenol, was associated with anxiety and fear, although this was masked for women by the orange aroma, lowering their anxiety; for men this was only minor (Lehrner et al. 2000).

Another study set out to demonstrate the gender effect of odour on pain perception: 20 men and 20 women were exposed to pain by holding a hand in hot water while smelling previously selected odours. Separate analyses for men and women revealed a significant effect of odour on pain perception for women but not for men, and when the odour was found to be pleasant women demonstrated a significant reduction in pain perception (Marchand & Arsenault 2002). The gender difference was shown in a different light when subjects proofread pages of text containing misspelt words: all participants performed significantly better when aroma was present in the room; lavender produced the greatest effect on women, whereas peppermint had the greatest effect on men (Kliauga, Hubert & Cenci 1996).

Miyazaki, Motohashi & Kobashaya (1992a) investigated the effects on females of inhalation of orange oil (unspecified), Chamaecyparis taiwanensis lig. [hinoki] and menthol, and found an increase in speed performing a mental task and a decrease in the number of mistakes for all three aromas. Profiles of mood state (POMS) scores indicated that depression/dejection, anger/hostility and tension/anxiety decreased after inhalation of the oils, whereas fatigue scores tended to increase.

A similar study explored the effects of inhalation of orange oil (unspecified), Chamaecyparis taiwanensis lig. [hinoki] and eugenol on the mood of six male individuals, and POMS were monitored: blood pressure showed a decrease after inhalation of hinoki or orange oils, but an increased heart rate with eugenol. Eugenol was deemed to be unpleasant and scores indicated increases in fatigue, depression/dejection, confusion and anger/hostility and a decrease in vigour, whereas inhalation of hinoki oil had the opposite effect (Miyazaki, Motohashi & Kobashaya 1992b).

Pleasant smells give pleasure and feelings of self-esteem (Baron 1990, Nezlak & Shean 1990) and the effect on women may be greater because, according to Herz and Cupchik (1992), women have more intense odour memories than men.

Although it is understood that personality can bias sensory perception, Chen and Dalton (2005) say that the emotional state of a person has a similar effect. Subjects were exposed via video clips to prime happiness, sadness, negative/hostility and neutral feelings. The time taken to detect odours (suprathreshold odours of pleasant, unpleasant and neutral) and the intensity of the odours was recorded. It was found that females reacted faster to smells with emotional links than to neutral smells. Emotional states augmented the intensity of odours for males.

The skin of women is more permeable than that of men to toxic chemical molecules having a similar size to those of essential oil compounds, and they can retain more fat-soluble compounds in their body and so are affected more (Eisberg 1983).

It is interesting to note that almost all practising aromatherapists and users of aromatherapy products are women, only about 2% of men being involved: this is perhaps because the overall effects of essential oils on women are more significant than on men.

Anosmia – absence of the sense of smell

If a person has poor vision, it is obvious by the wearing of spectacles or using a white stick, but there is no easy means of recognizing a person’s inability to smell. Aromas are made up of individual chemicals and each cilium is equipped with uniquely contoured depressions into which a single aroma molecule can fit, somewhat like a jigsaw puzzle. If the appropriate ‘dock’ for the molecule being inhaled is absent, that smell will not be registered.

Trials

When aromas are used therapeutically in clinical contexts they may be working in different ways at the same time. For example, lavender oil may:

The placebo effect must be taken into account when conducting trials using aromas, because the memory, attitude and expectations of the subject may modify the outcome, in addition to any effects of the aroma employed.

The use of olfaction in aromatherapy will increase and it is imperative that aromatherapy is put on a surer footing than at present; this can be achieved by the thousands of therapists currently in practice, who should not be deterred from embarking on clinical trials. With a little expert help in setting up a simple trial, much useful information could be gained in a relatively short time. Kirk-Smith (1995), in his review of therapeutic processes involving olfaction, agrees that further clinical evaluation of olfaction in therapy is needed, but trials involve many skills (therapeutic and scientific) and expectations or perceptions about the odour, as well as pleasantness, must be taken into account when predicting effects. It is not a simple matter to ascribe any reported benefits from the use of an aroma directly to that aroma. As mentioned above, it is imperative that the aromatic materials used in any future trials be precisely identified, otherwise the value of the tests will be diminished or negated.

Olfaction

Changes in thinking about odour reception have occurred following the identification of a very large family of genes responsible for coding olfactory receptors (Buck & Axel 1991).

People may have a sensitive sense of smell yet have poor perception and have difficulty in describing a smell; this is because olfactory input is widely distributed in the amygdala and the phylogenetically primitive cortex, without direct projections to the neocortex (Klemm et al. 1992).

The nose has two distinct functions:

An average human breathes in about 8 L of air each minute and more than a million molecules are taken in with each breath, yet even a remarkably small number of odorous molecules mixed in the air intake can be detected by humans (Engen 1987).

Inhalation

When essential oils are inhaled, the volatile molecules are carried by eddy currents to the roof of the nose, where delicate cilia protrude from the receptor cells into the nose itself. When the molecules lock on to these ‘hairs’ an electrochemical message is transmitted via the olfactory bulb and olfactory tract to the limbic system (amygdala and hippocampus). This may trigger memory and emotional responses, which can cause messages to be sent via the hypothalamus to other parts of the brain and the rest of the body (Fig. 7.1). Mainland and Sobel (2006) say that sniffing is necessary for olfactory perception and that a typical human sniff has a duration of 1.6 seconds, an average inhalation velocity of 27 L/min and a volume of 500 cm³. Sniffs are not merely a stimulus but are rather a central component of the olfactory perception, they also

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• affect odour intensity perception and identity perception

• drive activity in the olfactory cortex

• are rapidly modulated by an olfactomotor system

• are sufficient to generate an olfactory perception even in the absence of an odour.

Figure 7.1 • Aroma ? Inhalation Pathways

Humans recognize fewer molecules than other mammals, but can discriminate among 10,000 different odours (Menini et al 2004). The received messages are converted into action, resulting in the release of euphoric, relaxing, sedative or stimulating neurochemicals.

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The limbic system, which developed 70 million years ago and used to be called the rhinencephalon (from the Greek rhis = nose, enkephalon = brain), is heavily implicated in the expression of emotion, although whether it generates emotions or merely integrates them is not clear (Stoddart 1990). The body can replace olfactory nerve cells, an unusual feature of human nerve tissue, which serves to emphasize their importance.

Fibres from the olfactory nerve carry impulses to two small but significant parts of the brain, the locus ceruleus (where noradrenaline (norepinephrine) is concentrated) and the raphe nucleus (serotonin) (Godfrey-Hardinge 1993 personal communication). It is suggested that sedative aromas such as Origanum majorana [sweet marjoram], Lavandula angustifolia [lavender], Chamaemelum nobile [Roman chamomile], Matricaria recutita [German chamomile] and Citrus aurantium (flos) [neroli] cause stimulation of the raphe nucleus, which then releases the neurochemical serotonin, whereas stimulating aromas such as Rosmarinus officinalis [rosemary], Citrus limon (per.) [lemon], Ocimum basilicum [basil] and Mentha x piperita [peppermint] will affect the locus ceruleus, which then releases noradrenaline.

The use of essential oil aromas in aromatherapy treatments is not too far removed from intranasal drug delivery in common use today, e.g. steroid inhalers for allergies, peptides and anaesthetics (Chen, Su & Chang 1989). Lavender, which has been used in the treatment of insomnia (Hardy, Kirk-Smith & Stretch 1995), consists largely of oxygenated terpenes, which interact with cell membranes to suppress cell action potentials (Teuscher et al. 1990) and might account for a sedative effect. Animal tests using 42 essential oils and their components showed linalyl acetate and linalool from lavender oil to have the most sedative consequences (Buchbauer et al. 1993): a serum level in line with intravenous injection was produced, possibly owing to ready absorption by nasal and lung mucosa (Buchbauer et al. 1991). The use of an essential oil for such a purpose has advantages, as lavender oil

• does not have unwanted side effects

• can be used to vary long-term treatment, giving relief from powerful drugs and their side effects

• masks malodours usually present in psychogeriatric wards.

Warren et al. (1987) patented the use of a stress-reducing fragrance which included nutmeg oil. Subjects were stressed, and with nutmeg oil present systolic blood pressure was reduced and subjects rated themselves as being calmer and less anxious. Nutmeg oil contains the phenolic ethers myristicin and elemicin, which convert to the hallucinogens TMA (trimethoxyamphetamine) and MMDA (methoxymethylene-dioxyamphetamine).

In their paper on the use of fragrances and essential oils as medicaments, Buchbauer and Jirovetz (1994) drew the conclusion that interaction between fragrance molecules and receptors in the central nervous system (in combination with reflectoric effects) is responsible for the sedation caused by the inhalation of fragrances or essential oils.

Many odorants stimulate not only the olfactory system via the first cranial nerve but also the trigeminal system via the fifth cranial nerve, which enervates the nasal mucosa. The trigeminal system is part of the body’s somatosensory system and mediates sensations such as itching, burning or warmth and cooling: potent trigeminal stimulants such as ammonia and menthol have been used as smelling salts to arouse those who have fainted (Heuberger 2010).

Aromas affect emotions

Aromas are important in everyday life, though notoriously difficult to describe. We are surrounded by aromas, some natural but many synthetic. There are many natural aromatic messages, e.g. babies are able to recognize their own mother by her individual odour; also, synchronous menstruation occurs in groups of women living in close proximity, e.g. nuns.

Fragrances are added to almost everything from floor polishes to foods in order to

These aromas are inflicted on us regardless of our wishes and feelings – like background music – and the short- and long-term effects on people are not always known, since the emotions produced can be strong and unforgettable. The psychosomatic effect of smell is experienced by most people: for example the unfamiliar mixture of odours encountered in hospitals can produce a feeling of dread, accompanied by physical manifestations such as sweating, nausea and fainting (in visitors as well as patients), and the memory of the smell of some school meals can affect the appetite throughout life.

Essential oils consist of natural molecules and at the very least are to be welcomed as a means of introducing a natural product into the synthetic hospital environment. The use of carefully selected essential oils makes good sense both therapeutically and financially, for they are simple and inexpensive to use and no costly equipment is required. (see Table 7.2)

Table 7.2 Effects on the emotions mentioned by various authors. The figures indicate the number of times each is mentioned

The emotional and content qualities of autobiographical memories evoked by three memory-cue items (campfire, fresh-cut grass and popcorn) were presented in an olfactory, visual and auditory form by Herz (2004). The results showed that memories recalled by odours showed significantly more emotional and evocative content than those recalled by the visual or auditory forms. Herz argued that the data presented in his paper contributed to the growing body of evidence indicating a privileged relationship between olfaction and emotion during recollection.

Conditioning, pairing

Classic conditioning using a visual or an auditory stimulus requires many pairings, but in the case of olfaction sometimes only one pairing is needed, e.g. conditioning the body’s production of natural killer (NK) cells, fever and cytotoxic T-lymphocytes (CTL) to camphor (see below). The connection between the olfactory and immune systems is important for species survival (Hiramoto et al. 1993). Taste and odour pair easily with illness, which is useful in some cases, but an odour may become associated with an unwanted state or an illness. Aversive conditioning using an odour has been used to control overeating and resulted in a significant loss of weight compared with a control group (Foreyt & Kennedy 1971).

Examples of pairing are:

A neutral odour can be paired with an emotional state in a single session, so that it will evoke the same emotional state in different circumstances later. This effect is quite strong and it is not even necessary for the aroma to be perceived either during the pairing or when evoking the state; this is likely to be due to olfaction’s relative lack of representation in the neocortex (Kirk-Smith, Van Toller & Dodd 1983). King (1988) has similarly paired a ‘sea fragrance’ with relaxation training, measuring the effects of fragrance alone with forehead EMG (electromyography). Rose and Behm (1994) found that inhalation of the vapour from an extract of black pepper served to reduce the withdrawal symptoms experienced on cessation of tobacco smoking; essential oils containing citral are also said to have this effect.

Sedative/stimulant influence of odours

It has long been known that aromas have an effect on the psyche; incense was used first as a calming agent to induce a state of contentment (Lee & Lee 1992) and there are many examples: in ancient Greece, the physician Galen recommended the use of aromatic herbs against hysterical convulsions; burning bay leaves were inhaled by the Oracle at Delphi to induce a trance-like state to enable communication with the gods. Later, aromatic woods were burned to drive out ‘evil spirits’.

Almost a century ago a series of experiments on rats provided confirmation of the anecdotal sedative effects of some oils: when relaxing oils were dispersed in the air the rats took longer to perform tasks (Macht & Ting 1921): oils used included lavender, rose and valerian (common names only given). This method is effective because of the large area in the lungs available for the absorption of airborne oils into the bloodstream (Jirovetz et al. 1992).

Gatti and Cayola looked at the action of essences on the nervous system (1923a), the therapeutic effects of essential oils (1923b) and the use of valerian oil as a cure for nervous complaints (1929). They noted that the physical effects of the sedative/stimulant action of the oils were achieved more quickly by inhalation than by ingestion, and that opposite reactions could be obtained depending on whether the dose was small or large.

Since these early days more experiments have been carried out and knowledge of the psychotherapeutic effects of essential oils has grown, but nevertheless more research is needed; aromatherapy works, but it is necessary to find out how. Some interesting studies illustrating calming, stimulating and other effects are given below.

Many patients undergoing magnetic resonance imaging (MRI) body scans find them distressing and claustrophobic; this expensive procedure can be aborted by a stressed patient pressing the panic button, wasting both time and money. At the Memorial Sloan-Kettering Hospital in New York, a fragrance (constituents unknown) is used to calm patients receiving whole-body scans. Redd et al. (1994) administered bursts of heliotropine (a vanilla-like scent) to patients undergoing this procedure which reduced recalled anxiety by 63% in those who liked the smell. The calming brought about was thought to be attributable to the pleasing effect of the aroma, as pleasant conditions make stress more bearable.

According to Dember and Warm (New Scientist 1991), people do much better in a task that requires sustained attention if they receive regular puffs of an aroma. The test of concentration involved staring for 40 minutes at a pattern on a computer screen and hitting a key whenever the pattern changed very slightly. People generally did well to begin with, but performance eventually fell off and the fragrance effect was likened to a mild dose of caffeine. Peppermint was found to be stimulating and lily of the valley relaxing.

A traditional use of peppermint oil in aromatherapy was confirmed by Parasuraman (1991) when it was shown that peppermint aroma enhanced the sensory pathway for visual detection, allowing more control over attention; also rosemary (39% 1,8-cineole) was shown to be refreshing and to improve locomotor activity in mice (Buchbauer 1988).

The aroma of jasmine has been shown to stimulate mental function (Sugano 1989) and to shorten pentobarbital-induced sleeping time in mice (Kikuchi et al. 1989); cis- and trans-phytol were considered the stimulant-like compounds in a solvent-extracted oil. The sedative influence of lavender and the excitatory effect of jasmine in humans were confirmed by (Karamat et al. 1992). Sugano (1989) also showed that inhalation of lavender and the compound α-pinene had a sedative effect.

Aromas, memory and mood

Aromas can be employed easily and safely by using diffusers in rooms and cars, placing on tissues etc., and used in these simple ways they can improve sleep quality, change mood positively, alleviate stress and improve alertness. Aromas are able to remind people of past experiences, even from childhood, and when experienced during a learning process can aid recall of the information – this is sometimes known as ‘context-dependent learning’. Much of this has been known anecdotally for some time, but there are now numerous studies showing that aromas do affect human conditions. In 1989, Rottman found that the aroma of jasmine in a room improved performance in problem-solving tests, and Schab (1990) found that the presence of an ambient aroma during a learning process brought about 50% better recall than when no aroma was present; Smith, Standing and Deman (1992) had a similar result. The effects of Rosmarinus officinalis [rosemary] and Lavandula angustifolia [lavender] were tested on 140 subjects divided into three groups, one being a control group. Either the lavender or the rosemary was diffused into a test cubicle prior to the test:

The effects of aromatherapy on relaxation, alertness, mood, anxiety and EEG (electroencephalogram) were investigated in 40 subjects using lavender (unspecified) or rosemary (unspecified) essential oil diluted 10% in grapeseed oil and inhaled from a cotton swab. The rosemary group had increased alertness (decreased frontal α and β power) and were faster but not more accurate in mathematical computations. The lavender group performed the mathematics more quickly and more accurately, and the EEG recordings showed a stronger β power, suggesting increased drowsiness; both groups felt more relaxed, and it was concluded that aromas do affect psychological and physiological states (Diego et al. 1998).

Skamoto et al. (2005) investigated the effect of exposure to lavender aroma during rest periods at work. The workers carrying out a computer task requiring concentration (60 minutes’ work interspersed with 30 minutes’ rest) were divided into three groups:

The afternoon sessions when concentration was lowest showed a positive effect for lavender over the control and jasmine groups. This finding is interesting because although lavender is usually thought of as having a sedative effect (perhaps the lavender allowed for a more efficient rest period), it is known that it is amphoteric and can also have an arousing effect.

Moss et al. (2003) concluded that the aroma of essential oils produced objective effects on cognitive performance and subjective effects on mood: Zoladz and Raudenbush (2005) showed that cinnamon and peppermint aromas improved subjects’ ability to pay attention, their recognition and working memory, visuomotor response speed, mood and energy. In a study to assess whether peppermint could increase the alertness of clerical workers in an office environment, typing accuracy, speed, increased performance and ability to alphabetize improved significantly (Barker et al. 2003).

Another study showed that aromas can influence the way people think and behave (Baron 1990). Subjects were put in a room that was intermittently fragranced with air freshener; under these conditions they set themselves higher goals, were more inclined to negotiate in a friendly manner and were able to resolve conflicts more successfully.

A study was carried out by Raudenbush, Corley and Eppich (2001) to determine whether physical tasks would be enhanced by the inhalation of peppermint aroma; athletes performed four tasks:

Participants performed the protocol twice under different odour conditions, first with a peppermint-odorized adhesive strip under the nose, and second with an odourless adhesive strip. The peppermint aroma resulted in increases in running speed, hand grip strength and number of push-ups, but had no effect on the skill-related basketball free-throw shots.

In a different study athletes performed a 15-minute treadmill stress test and at 3-minute intervals 50 mL of beverage (water with peppermint aroma added, unadulterated water, or a commercial sports drink) were consumed: in the control condition no beverage was consumed. Both the peppermint drink and the sports drink led to greater ratings of personal performance and increased mood (Schuler, Rawson & Raudenbush 2004).

Matricaria recutita [German chamomile] oil has been used to study the effects of olfaction on mood and imaging. When subjects were asked to visualize positive or negative phrases following exposure to either chamomile oil vapour or placebo, the oil significantly increased the time it took for images to be produced, suggesting either that enhanced neural processing was taking place or that the oil was sedative; it also shifted mood rating in a positive direction (Roberts & Williams 1992).

Psychophysiological effect of aroma

There can be no doubt that changes in physiological and psychological parameters can be caused by essential oil inhalation, and Miyazaki et al. (1991) reported that changes in mood due to inhalation could be measured using the light reflex of the pupil; they also found that orange oil (unspecified) increased the activity of the parasympathetic nervous system. Using encephalography (EEG) and psychological scoring to examine the effects of inhalation of various oils, it was found that bitter orange oil increased sleeping time significantly under conditions of mental stress. In psychophysiological studies of fragrance by Sugano and Sato (1991) it was concluded that lavender, orange and rose would elevate work efficiency and counter the effects of a stressful life; chamomile, jasmine and musk increased β-band microvibrations, suggesting mental stimulation.

These studies demonstrated that psychological and physiological parameters can be changed by the inhalation of essential oils, but the oils used in most of the tests cited in this section were not properly identified. Lavender was found to be unpleasant in some tests (Klemm et al. 1992, Lorig & Roberts 1990) but pleasant in others (Torii et al. 1988); there are similar findings with jasmine. It is hard to imagine that Lavandula angustifolia could consistently be rated as unpleasant, whereas it is entirely possible that L. latifolia or L. stoechas (among others) could merit this description: the ester content of lavenders grown in different regions can vary from 8% to 50%, altering the aroma considerably; jasmine oil is not distilled and contains traces of chemical solvent. It is astonishing that time and money can be spent in research without ascertaining what materials are being tested and studied, but this has happened, which tends to detract from the value of the whole exercise.

Klemm et al. (1992) studied the physiological responses of 16 young women to aromas from seven essential oils (birch tar, galbanum, heliotropine, jasmine, lavender, lemon and peppermint) assessed by EEG recordings from 19 locations on their scalps. Subjective responses to the odours differed, but the most consistently arousing and strong odours included galbanum, lavender, lemon and peppermint. The most pleasant were lemon and peppermint, whereas birch tar, galbanum and lavender were consistently unpleasant. All aromas affected the EEG in at least some subjects, and all subjects responded to some.

It is not clear from studies carried out whether or not personal like or dislike of the odour has a real bearing on the effects of essential oil inhalation. Bulgarian rose, lavender and geranium oils were tested on 48 medical students by spraying a 1% solution into the room; there was an increase in concentration, attention span, work rhythm and a shortening of reflex times; these effects were independent of personal like/dislike of the aroma (Tasev, Toleva & Balabanova 1969). On the other hand, the study by Marchand and Arsenault (2002) came to the conclusion that if the aroma was found to be pleasant then mood perception was significantly increased, whereas unpleasant aromas significantly reduced mood perception. Practical experience shows that essential oils work in an aromatherapy treatment even if the aroma is not liked, although the client tends to be more relaxed and more ready to accept treatment with a positive outlook if the aroma is perceived as pleasant.

Summary

Great advances have been made in our knowledge of the interactions of the mind, emotions and nervous and immune systems, and there is growing recognition of their combined impact on general health. Essential oils have an effect on everyone and have an important role to play in bringing about a state of relaxation, thereby favouring healing – aromas are effective even during sleep or unawareness of their presence. Everyone is capable of deriving benefit from aromatherapy.