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The Smell Report

The Smell ReportAn overview of facts and findingsKate FoxDirectorSocial Issues Research CentreThe human sense of smellAlthough the human sense of Smell is feeble compared to that ofmany animals, it is still very acute. We can recognise thousandsof different smells, and we are able to detect odours even ininfinitesimal smelling function is carried out by two small odour-detecting patches - made up of about five or six millionyellowish cells - high up in the nasal comparison, a rabbit has 100 million of these olfactoryreceptors, and a dog 220 million. Humans are nonethelesscapable of detecting certain substances in dilutions of less thanone part in several billion parts of air.

The Smell Report An overview of facts and findings Kate Fox Director Social Issues Research Centre

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Transcription of The Smell Report

1 The Smell ReportAn overview of facts and findingsKate FoxDirectorSocial Issues Research CentreThe human sense of smellAlthough the human sense of Smell is feeble compared to that ofmany animals, it is still very acute. We can recognise thousandsof different smells, and we are able to detect odours even ininfinitesimal smelling function is carried out by two small odour-detecting patches - made up of about five or six millionyellowish cells - high up in the nasal comparison, a rabbit has 100 million of these olfactoryreceptors, and a dog 220 million. Humans are nonethelesscapable of detecting certain substances in dilutions of less thanone part in several billion parts of air.

2 We may not be able tomatch the olfactory feats of bloodhounds, but we can, forexample, track a trail of invisible human footprints across cleanblotting human nose is in fact the main organ of taste as well assmell. The so-called taste-buds on our tongues can onlydistinguish four qualities - sweet, sour, bitter and salt -all other tastes are detected by the olfactory receptors high up in ournasal passagesVariationsOur smelling ability increases to reach a plateau at about the ageof eight, and declines in old age. Some researchers claim that oursmell-sensitivity begins to deteriorate long before old age,perhaps even from the early 20s. One experiment claims toindicate a decline in sensitivity to specific odours from the age of15!

3 But other scientists Report that smelling ability depends onthe person s state of mental and physical health, with some veryhealthy 80-year-olds having the same olfactory prowess as consistently out-perform men on all tests of smellingability (seeSex differences, below).1 Schizophrenics, depressives, migraine sufferers and very-low-weight anorexics often experience olfactory deficits ordysfunctions. One group of researchers claims that certainpsychiatric disorders are so closely linked to specific olfactorydeficits that Smell -tests should be part of diagnostic supplements have been shown to be successful in treatingsome Smell and taste smoking does not always affect scores on Smell -tests, itis widely believed to reduce recent study at the University of Pennsylvania suggests that,contrary to popular belief, blind people do not necessarily have akeener sense of Smell than sighted people.

4 In their experimentson blind and sighted people, the top performers on most testswere (sighted) employees of the Philadelphia Water Departmentwho had been trained to serve on the Department s water qualityevaluation panel. The researchers conclude thattrainingis thefactor most likely to enhance performance on Smell tests.(University of Pennsylvania researchers are probably fairlyclued-up on this subject - they designed the University ofPennsylvania Smell Identification Test (UPSIT) which is thestandard test used in almost all experiments.)The importance of training in the development of Smell -sensitivity is confirmed by many other studies. Indeed, this factorcan sometimes be a problem for researchers, as subjects inrepetitive experiments become increasingly skilled at detectingthe odours researchers have to be very careful about theodours they use in experiments, because a Smell is not always asmell.

5 Many odorous substances activate not only the olfactorysystem but also the somatosensory system -the nerve endings inour noses which are sensitive to temperature, pain etc. This iswhy anosmics - patients who have completely lost their senseof Smell - can still detect menthol, phenylethyl alcohol and manyother substances. In a study testing anosmics ability to perceiveodorous substances, it was found that many so-called odours arein fact affecting the pain- and temperature-sensitive nerve-endings, rather than the olfactory receptors. Out of 47 odorous 2substances, anosmics could detect 45. (Only two substancescould not be detected by the anosmic patients: these weredecanoic acid and vanillin, which affect only the olfactoryreceptors, and can thus safely be classified as pure odours.)

6 Some unpleasant smells do more than just annoy or disgust us,they actually cause us Smell -identification ability increases during childhood,even newborn infants are highly sensitive to some importantsmells: recent research shows that newborn babies locate theirmothers nipples by Smell . In experiments, one breast of eachparticipating mother was washed immediately after the birth. Thenewborn baby was then placed between the breasts. Of 30infants, 22 spontaneously selected the unwashed experiments have also shown that babies are responsive tovery faint differences in body odour, but it is believed thatinfants are highly sensitive only to specific smells, rather than awide range of terms of odourpreference, however, one significant studyshowed that 3-year-olds have essentially the same likes anddislikes as conducted in the early 70s and replicated in 1994revealed that children do not develop sensitivity to certain odoursuntil they reach puberty.

7 In these studies, 9-year-olds showed apronounced insensitivity to two musk odours, although theirability to detect other odours was the same as that ofpostpubescents and perception of Smell consists not only of the sensation of theodours themselves but of the experiences and emotionsassociated with these sensations. Smells can evoke strongemotional reactions. In surveys on reactions to odours, responsesshow that many of our olfactory likes and dislikes are basedpurely on emotional association of fragrance and emotion is not an invention ofpoets or perfume-makers. Our olfactory receptors are directlyconnected to the limbic system, the most ancient and primitivepart of the brain, which is thought to be the seat of sensations are relayed to the cortex, where cognitive recognition occurs, onlyafterthe deepest parts of our brains havebeen stimulated.

8 Thus, by the time we correctly name a particularscent as, for example, vanilla , the scent has already activatedthe limbic system, triggering more deep-seated there is convincing evidence that pleasant fragrancescan improve our mood and sense of well-being, some of thesefindings should be viewed with caution. Recent studies haveshown that ourexpectationsabout an odour, rather than anydirect effects of exposure to it, may sometimes be responsible forthe mood and health benefits reported. In one experiment,researchers found that justtellingsubjects that a pleasant orunpleasant odour was being administered, which they might notbe able to Smell , altered their self-reports of mood and well-being.

9 The mere mention of a positive odour reduced reports ofsymptoms related to poor health and increased reports of positivemood!More reliable results have been obtained, however, fromexperiments using placebos (odourless sprays). These studieshave demonstrated that although subjects do respond to someextent to odourless placebos which they think are fragrances, theeffect of the real thing is significantly greater. The thought of4pleasant fragrances may be enough to make us a bit morecheerful, but the actual Smell can have dramatic effects inimproving our mood and sense of olfactory sensitivity generally declines with age,pleasant fragrances have been found to have positive effects onmood in all age experiments involving stimulation of the left and right nostrilswith pleasant and unpleasant fragrances, researchers have founddifferences in olfactory cortical neurone activity in the left andright hemispheres of the brain which correlate with the pleasantness ratings of the odorants.

10 These studies are claimedto indicate that positive emotions are predominantly processed bythe left hemisphere of the brain, while negative emotions aremore often processed by the right hemisphere. (The pleasant odorant used in these experiments, as in many others, wasvanillin.)Perception effectsThe positive emotional effects of pleasant fragrances also affectour perceptions of other people. In experiments, subjects exposedto pleasant fragrances tend to give higher attractiveness ratings to people in photographs, although some recent studies haveshown that these effects are only significant where there is someambiguity in the pictures. If a person is clearly outstandinglybeautiful, or extremely ugly, fragrance does not affect ourjudgement.


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