A Failure of Aromatherapy?
Exposure to Odor Worsens the Perception of Pain
G Neil Martin, MA, PhD, FRSAThis article describes what happened when 60 healthy men and women experienced experimentally-induced pain during exposure to either a pleasant odor (lemon), an unpleasant odor (machine oil) or no odor. Participants reported the degree of pain they experienced at five minute intervals for 15 minutes. Individuals exposed to both odors reported significantly greater pain than did the participants in the control condition at five minutes. At 15 minutes, individuals exposed to the unpleasant odor experienced greater pain than did the control group. The results suggest that exposure to odor is not beneficial to those seeking pain relief. Rather, its perception is associated with greater pain than is no odor.
Although over £20 million was spent on over-the-counter aromatherapy products in 1998  and 75% of respondents in one study considered it effective , little evidence exists that the administration of odor (usually an essential oil) can alleviate the symptoms of mental or physical ill-health .
Odor can exert significant effects on mood and cognition [4-6], but well-controlled empirical studies of the effect of odor on ill-health show a mixed, but generally negative pattern of results . One study reported no direct analgaesic effect of inhaling the odors of lavender and rosemary , another found an ameliorating effect of odor only in women , and others have found no statistically significant effect on patients’ ill-health .
To examine whether odor can affect or modulate the experience of aversive experiences, the current study tested the strongest form of the aromatherapeutic hypothesis: the suggestion that exposure to a pleasant odor can alleviate pain. We required men and women to endure experimentally-induced pain for a maximum of 15 minutes, in the presence of either a pleasant or unpleasant odor or no odor. We reasoned that if a pleasant odor is effective in alleviating pain, participants should report a lower degree of pain than those in the control and unpleasant conditions.
The study also tested two theories of attention and pain. The distraction hypothesis argues that any perceived sensory, environmental stimulus is sufficient to reduce experienced pain because the stimulus is drawing attention away from the pain and the source of pain thus reducing the cognitive resources available to focus on the pain [11,12]. The emotional distractor hypothesis argues that in order for a stimulus to distract a person from his or her pain, it must first be perceived as pleasant; an unpleasant stimulus detected during the experience of pain will lead to an increase in the perception of pain [13,14]. If the distraction hypothesis is correct, exposure to any odor will lead to a reduction in the perception of pain. If the emotional distractor hypothesis is correct, then exposure to the pleasant odor will lead to a reduction in perceived pain whereas exposure to unpleasant odor will lead to an increase in perceived pain when compared with the other two conditions.
Study ResultsThirty healthy men and 30 healthy women (average age= 23 years), free of respiratory infection and with normal ability to detect odors, were randomly assigned to three conditions: pleasant odor, unpleasant odor, no odor, with equal numbers of men and women in each condition. The odors were supplied by Aroma Co. and were diffused using an AromaCube™. In the pleasant condition, lemon odor was diffused 20 minutes before the experiment began. In the unpleasant odor condition, the same procedure was adopted with machine oil. Control participants received no odor.
The participants were seated at a desk in a comfortable, well-lit, minimally decorated room and placed their non-dominant arm in a bucket of uncirculated water and ice for up to 15 minutes (the cold-pressor test). They rated the degree of pain they felt at 5-minute intervals. The researcher was present in the adjacent room and could monitor participants at all time. Participants placed a mark along an 11-centimeter line which corresponded to how they felt at that moment (1=no pain at all; 11= unbearable pain). All participants reported various degrees of pain during the experiment, all undertook the experiment for 15 minutes and none expressed a wish to abandon the study. Before and after the cold-pressor test, participants rated the room on various dimensions (relaxing, pleasant-smelling, warmth, comfort) on a 11cm-line scale.
The study found these effects:
In terms of current theories of pain and attention, the result is intriguing because all distractors—pleasant and unpleasant—were associated with increases in self-reported pain in the early stages of pain perception. One explanation for this finding might be that, although the pleasant odor was regarded positively, it may have been too alerting. Lemon scent is pleasant but refreshing—as those of others  have demonstrated—and might, therefore, have heightened participants’ vigilance. This alertness, in turn, may have made the participants more aware of the pain they were experiencing by directing sensation and perception to these aversive stimuli. Alternatively, it is possible that the mere presence of conspicuous and distinctive stimuli drew attention to the participants’ experience of pain, rather than distracting them from it, in the same way that an intrusive noise might. The increased pain in response to exposure to machine oil might be viewed as supporting the emotional distractor hypothesis and is consistent with studies showing that aversive distractors are associated with increases in pain perception , but this explanation is confounded by the general increase in pain experienced by those inhaling odor.
The current study extends previous findings by showing that the number of aversive distractors that can enhance pain perception can include unpleasant odors. Importantly, we have demonstrated that exposure to pleasant and unpleasant ambient odor can increase pain perception, possibly by drawing attention to the experience of pain in its early stages. The current study employed odors described as pleasant and unpleasant. Future study might usefully compare whether a pleasant-relaxing and a pleasant-alerting odor has differential effects on pain perception. This would help determine whether all pleasant scents can increase pain perception or whether the odor must be characterised by some property that enhances vigilance.
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Dr. Martin is Principal Lecturer in Psychology and chairs the Psychology Research Team at the Middlesex University School of Health and Social Sciences in London, England.
This article was posted on April 7, 2006.