12 October 2019 | New Scientist | 45off in sweat, breath, urine and faeces.
Even without medical training, we find
an individual’s sweat more intense and less
pleasant when they are ill, says Mats Olsson
at the Karolinska Institute in Sweden.
His experiments reveal that, via sweat, we
subconsciously detect when someone else’s
immune system is ramped up in response to
an infection, and our own leaps into action.
Being repulsed by particular body odours
can help us avoid other dangers too. “Kin
recognition serves two main purposes: one
is bonding, the other is incest avoidance,”
says Croy. That would explain the finding
that parents come to dislike the smell of
their opposite-sex children when they reach
puberty. The scent of aggression may put us
on alert too. Bettina Pause at Heinrich Heine
University Dusseldorf, Germany, has found a
distinctive response in the sensory processing
part of women’s brains when they sniff sweat
from aggressive men, something she believes
evolved to help women avoid violence.Sickly smell
An obvious reason why, unlike other
mammals, we work hard to wash away our
smells is that we understand the link between
poor personal hygiene and disease – we know
that washing can increase our chances of
survival. In fact, anthropologists argue that
our changing attitudes towards personal
hygiene coincided with the rise of urbanisation
around the industrial revolution, says Asifa
Majid at the University of York, UK.
Natsch points out that there is a much
longer history of personal hygiene in East Asia,
which might help explain the curious fact that
many Asian people have naturally odourless
armpits. Thanks to a one-off genetic mutation
of the ABCC11 gene, 95 per cent of ethnic
Chinese people and some 70 per cent of East
Asians don’t produce chemical precursors
of armpit odours. We don’t know when the
mutation happened, says Natsch, but an
aversion to BO would have helped it succeed.
All this goes some way to explaining our
distaste for bodily odours. However, there
are plenty of scents that we love – and not just
from those irresistible babies. In the right
circumstances, we appreciate even the most
pungent human odours. We are less disgusted
by the nasty odours of our nearest and dearest –
the so-called source effect, for example. And we
positively enjoy the smell of someone we are
sexually attracted to when dancing with them.
Sometimes context doesn’t even matter, says
Ferdenzi, recalling that, after her first study,anxiety in the body odours of others. Recently,
researchers from Sobel’s lab analysed
skydivers’ sweat during their first jump and
found it contained 29 volatile compounds
not present before. Similarly, using sweat
from cage fighters, Havlíček and his colleagues
discovered that people can identify winners
and losers, suggesting that smell helps us
recognise dominance.
Sobel’s team has also found that sniffing
tears resulting from negative emotions
lowers testosterone in men, possibly through
a volatile chemical called hexadecanal, which
modulates aggression in mammals. Some
work has even shown that smelling someone
else’s anxiety can promote empathy.
Less research has been done on whether
body odour conveys positive emotions, but it
has been shown that the scent of a loved one
can reduce stress. Ferdenzi believes that the
smell of positive emotions, even in strangers,
may help explain why happiness is contagious.
In not-yet-published work, her team has shown
that the smell of happy people produces feel-
good physiological responses in others.
Clearly BO evolved over millennia to
be a subtle and multifaceted channel of
communication, but the fact remains that
it often grosses us out. Why? One reason is
obvious: certain bodily odours are intended
to repel. This is true of smells connected
with disease. We can’t all be super-sniffers
like Joy Milne, the woman who can detect
the scent of Parkinson’s disease, but anyone
can learn to recognise a range of illnesses
including diabetes, pneumonia, cholera and
certain cancers from specific smells given
A host of online products
claim to offer sexual allure in
a bottle. They tend to contain
steroids found in armpit odours,
including androstadienone
and estratetraenol, suggested
as the first human pheromones
in 1991.
They are no such thing, says
Tristram Wyatt at the University
of Oxford. Pheromones trigger
specific behaviour when
smelled, but as yet there is
no robust evidence for any
particular ones with a role
in human sexual attraction.
“They were plucked out
of thin air,” says Wyatt, then
patented by a fragrance company
to add to perfumes. Many papers
have been published since,
but the research is like an echo
chamber. “There’s no more
evidence now than there was
then,” he says.LOVE POTION
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