Journal Number 89
December 2003

EDITORIAL

The Science of Scents 3
Sensuous Smells, Amorous Aromas, And The Odours Of Ardour

By Ian St George

Look up "fragrance" on the net and you have to wade through a mire of sexually-explicit or
-implicit websites touting aromatherapy body oils, sex attractants, love potions, pheromones
and fragrant candles. There are some big industries based on fragrance out there. And its all
about pheromones, folks.

Pheromones

Pheromones are volatile substances that act as sexual attractants for insects, and there is no
doubt that some orchids use them to attract pollinators. The first pheromone discovered was
from silkworm moths. A tiny amount of it made male moths beat their wings madly in a "flutter
dance". The chemically pure pheromone is called "bombykol" for the silkworm moth, Bombyx
mori from which it was extracted. It signalled, "come to me!" from great distances. If a single
female moth were to release all the bombykol in her sac in a single spray, all at once, she could
theoretically attract a trillion males in an instant.

Many mammals have an additional scent organ to perceive smells designed to alter their behaviour or physiology. It is known as the vomeronasal organ (VNO). It consists of two small pits with tiny openings in their centres about a tenth of a millimetre wide.

Dogs can distinguish between the smell of T-shirts worn by non-identical twins (they couldn't tell the difference between identical twins because they smell identical). Dogs, bees and horses can smell fear in humans. Other animals use olfaction to identify their young. Studies of the nursing behavior of mother-pup pairs of Mexican free-tailed bats showed that mother bats returned to areas where they had nursed previously; it appears scent cues are used to remember these places.

But although the human embryo develops a VNO, it then atrophies in adults. Like the appendix or the nictitating membrane of the third eyelid, our VNO has been thought to be vestigial, something we can do without. But now a group of American researchers claims to have discovered the VNO in humans, raising the possibility that we may be responding to pheromones too.

A Utah research group examined subjects who virtually all had VNO pits - about lcm up the nostril; they respond to quite different chemicals from those we can smell. And there seem to be clear gender differences - men's VNOs respond vigorously to steroids from the skin of a female and vice versa.

Not everyone is convinced: the Utah group raised $12 million to exploit the discovery, and is already selling "his and hers" pheromone perfumes. Nobody has been able to replicate their work. But if we are not affected by pheromones, why do we produce them? The fluid from our sweat glands mixes with fatty material from sebaceous and apocrine glands, both found around hair follicles, and bacteria act on the mix leaving pheromones as leftovers.

In puberty we grow hair in just those zones that fill with blood when we become excited, so they
heat up. The warmer they get, the more easily the bacterial leftovers evaporate. "Dancing close
and slow brings (most) men up against the apocrine and sebaceous supplies in her hair while
she can nestle in to those in his armpit. Think twice before applying that deodorant". Bleccchh.

But is that our VNO? or is it just ordinary olfaction? Scents do serve a recognition function.
We all have our own unique smell and can recognise and be recognised by our smell. Children
can distinguish between the smell of their siblings and other children of the same age. Babies
recognise their own mothers' smells and mothers recognise their own babies' smells.

Women can detect minute differences in male immunotype by smell. Immunity is conferred by
HLA genes in humans, and these also determine our individual smell. We prefer the smell of
people who have different HLA genes from our own, and that provides our offspring with an
evolutionary advantage - more different HLA genes would give them a greater degree of immunity. We tend to be repelled by people whose immunotype is similar to our own. Perhaps we choose our mates on the basis of smell.

Fragrance and Mood

Emotion can be communicated by smell. Women can discriminate between armpit swabs taken
from people watching happy or sad films, and they can detect the small of fear in the armpit
secretions of people who watched terrifying films. Men were less good at this. So sweat contains
a chemical signal which communicates the emotion. Furthermore armpit swabs taken from donor women at a certain phase in their menstrual cycle and wiped on the upper lip of recipient women can advance or retard menstruation in the recipients depending on the phase of the donor.

We seem to secrete compounds that can relay information about our mood to another person.
If we know what these compounds are can they be used to alter mood?

We know mood can be altered by smells that recall events in our lives - the scent of new hay rouses memories of the golden weather of childhood, and I am happy. If we smell (or taste something) before a negative experience, that smell (or taste) is linked to that experience. Could we put that effect to advantage? if smell were to be associated with a positive, healing treatment then could the smell itself substitute for the treatment once the link has been reinforced?

In one study insulin was injected into healthy men daily for four days and their blood glucose was measured (it fell). At the same time, they were exposed to a smell. On the fifth day they were just given the smell - and their blood glucose fell.

Perfume makers claim certain smells are of themselves relaxing (i.e. independent of relaxing
associations in people's memories). This can be tested with an electro-encephalogram (EEG).
One of the brain-waves measured by EEG is called the "alpha-wave". Increased alpha-wave activity is a sign of relaxation. Aromatherapy companies market perfumes with claims that they do relax you.

Does aromatherapy work? Researchers working with Prof Tim Jacob in Cardiff analysed the effect
of two essential oils, ylang ylang and rosemary, on alpha-waves. The protocol was to pre-relax the subjects, record the EEG for 2 mins and then apply the odour to a face mask, wait 3 mins and then record another 2 mins. The mask was then removed, 3 mins allowed for equilibration and a further 2 mins of control activity was recorded.

While there were clear trends (rosemary depresses alpha-activity while ylang ylang enhances it)
the results were not perfect. In aromatherapy rosemary is used as a stimulant and ylang ylang is
a soothing, relaxing aroma. The researchers concluded that ylang ylang and rosemary have measurable effects on brainwave activity, and in the direction anticipated from their reputed properties.

Scientific research has more often reported no effect for aromas on mood. The effects are most likely to be the result of memory conditioning an association. The mood effects probably also parallel the hedonicity of the odour (pleasant odours give rise to pleasant mood states while unpleasant odours give rise to unpleasant moods). Well yeah, but that assumes odours are inherently pleasant - ie they don't depend on memory associations.

The Extraction and Measurement of Fragrance

Swiss scent specialists at Givaudan are involved in perfumes by Calvin Klein, Cartier and even Michael Jordan. They recently assisted a California Academy of Sciences scientist Kim Steiner, who analysed the aromas of orchids with the help of equipment and expertise from Givaudan (it's good to hear of industry supporting science).

To collect a scent to study, Steiner would invert a glass dome over one or more flowers and pump the scent-infused air though a chemical "trap" that captured fragrances (Fig.1).

The pump had to run for several hours to obtain enough scent for a chemical analysis. He would then send the traps to his collaborators in the research labs of Givaudan.

After extracting the scents from the traps, they would inject them into a gas chromatograph-mass spectrometer that can identify the amounts and kinds of chemicals that make up a fragrance.

Givaudan uses these data to inspire new designer perfumes or candle scents. Steiner uses them
to understand how floral scents evolve among closely-related species that share a specialized
pollination system. He has been studying oil-producing orchids in the subtribe Coryciinae ,
which have pungent, soapy-smelling flowers, mostly pollinated by a single species of solitary oil-collecting bee.

New technology is appearing, bypassing the old chemical traps (usually volatile-absorbing solvent fats), and thus reducing the amount of fragrance needed for extraction, and thus the time taken: in one report solid-phase microextraction (SPME) and capillary gas chromatography-mass spectrometry (GC-MS) were developed for the identification of volatile compounds in consumer products. SPME minimizes sample preparation and concentrates volatile compounds in a solvent-free manner.

Volatile flavour and fragrance compounds were extracted by SPME from the headspace (the air above the liquid) of vials containing shampoos, chewing gums, and perfumes, and analysed by GC-MS. Headspace SPME was shown to be more sensitive than conventional headspace analysis of similar samples performed with an airtight syringe. Analysis times were less than 30 min, allowing multiple analyses to be performed in a typical laboratory class period.

Do you know? Astronauts tend to lose their sense of smell. This is thought to result from
congestion in the nose resulting from increased capillary pressure as the heart no longer has
to work against gravity. As a consequence the sinuses tend to fill up with fluid, giving rise to stuffiness similar to a head cold.

Acknowledgements
Material for this essay was gleaned from the following websites:
1. www.cf.ac.uk/biosi/staff/jacob/teaching/sensory/olfact1.html
2. www.schoolscience.co.uk/content/5/chemistry/smells/smellsch3pg1.html
3. www.dhushara.com/book/genes/mhc.htm
4. www.calacademy.org/science_now/where_in_the_world.html
5. www.hhmi.org/senses/d230.html