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On covering one's mouth (when yawning)

BMJ 2004; 328 doi: https://doi.org/10.1136/bmj.328.7445.963-a (Published 15 April 2004) Cite this as: BMJ 2004;328:963

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Yawning : comparative study of knowledge and beliefs,

Since Antiquity, yawning has held as little interest for
philosophers,
psychologists and physiologists, as it has for teachers, moralists and
physicians. And yet, few things are as common as yawning. Everyone yawns 5

to 10 times a day. Yawning is a recognized behaviour in almost all
vertebrates from birds to humans, one which starts in the womb and
continues until death. Although yawning often procures a sense of well-
being
for the yawner, attempting to mask this behaviour is standard practice.

Modern neuroscience is still looking for a complete explanation of
its
intimate mechanisms. But above all, its exact physiological purpose
remains a
subject of debate; some see yawning as a mechanism for stimulating
wakefulness [1], while others contest this view and instead link yawning
to the
effects of a homeostatic sleep factor accumulating throughout the waking
hours [2].

In this paper, we offer a broad-based cultural and medical overview
of
the related conceptions and myths through comparison of the popular and
medical views of Arabic, Western and Indian cultures. This will help us
support the idea that yawning should be covered during medical studies,
along with sleep and arousal disorders.

Beliefs
Arab countries

In 1923, Pierre Saintyves [3] surveyed cultural beliefs related to
the
meaning of yawning. According to Saintyves, Islam sees yawning as a sign
of
Satan entering the body, and sneezing as a sign of his leaving the body.
Assas-bou-Malek and others all date this opinion back to the Prophet:
“The
Prophet said that Satan endeavours to distract the faithful in prayer.
This is
Allah’s way of testing them. One way Satan distracts the faithful is by
dominating their thoughts, infiltrating their minds during prayer. Another

way is by making them yawn to divert attention away from their prayers.
The
Prophet told us that yawning is prompted by Satan and gave us the order to

avoid it whenever possible. When it becomes inevitable, we must close our
mouth with our hand.”

We recently came across this question on a website: “I am a 22-year-
old
devout practising Muslim with a problem I hope to overcome with Allah’s
help
and your advice. As soon as I begin my prayers, I start yawning
involuntarily.
And this continues even when I recite the Throne Verse. I really don’t
know
why I’m yawning dozens of times, over and over, during a single prayer. I
hope you can shed some light on my problem.”

Saintyves also writes: “According to Ibn Battal, attributing yawning
to Satan
means he wants us to yawn and takes pleasure in it; he enjoys this
disfiguring
behaviour because it makes men look ridiculous.” As to putting a hand over

the mouth, this gesture applies when the mouth is already open, as well as

when it is still closed, “because Satan enters…”. Instead of the hand, a
piece
of clothing or any other object may be used. The fear of Satan entering
the
body is linked to the fear of possession, which explains why this gesture
is
demanded of the faithful during prayer [4].

In India

In India, “bhuts” (spirits) are believed to prefer entering the body
through
the mouth. Yawning is therefore dangerous, because it entails two kinds of

risks: either bhuts will penetrate the body through the throat, or a part
of the
soul might escape. Since it would be very difficult to recapture, the
recommended practice is to put a hand in front of one’s mouth and say
“Marayan!” (Good God!), or crack one’s fingers to scare the bad spirit
away
[3].

In Europe

Around 590 AD, during the times of Pope Gregory the Great, a bubonic
plague epidemic raged through Europe, decimating the population and
inspiring numerous superstitions: “Yawning was fatal then, and the habit
of
signing the cross in front of the mouth originated during the times of the

plague. [...] There was a plague they called inguinal, because a bubo
appeared in the groins, causing men to die suddenly in the streets, in
their
houses, at play, during a meal. Their souls left their bodies when they
sneezed or yawned. This is why we said ‘God bless you’ to those who
sneezed. Those who yawned made the sign of the cross over their mouths”
[5].

It is possible that the love of perfumes in the royal European courts
in
the 17th and 18th centuries had its origins in the necessity to conceal
poor
body hygiene. Placing one’s hand in front of the mouth during yawning was
helpful in hiding appalling oral conditions and reducing the expiration of

nauseating odours. In a 2004 editorial for the British Medical Journal, G
Dunea [6] was surprised to see medical students yawning frequently as they

waited for their lecturer; moreover, 67.5% of the time they did not cover
their
mouths with their hands. He suggested this allowed students to avoid
bacterial contamination of their palms, ironically adding that it is
undoubtedly
better to let others marvel at your tonsils than to risk injuring your
elbow!
In medicine

In his treatise on wind, De flatibus liber, Hippocrates [7] noted
that “the
continual yawning of apoplectics proves that air is the cause of
apoplexies”,
thereby confirming his theory that “wind is the cause of all diseases”. In

1739, Hermann Boerhaave, in his Praelectiones academicae [8], explains
that
“yawning and pandiculation favour the equitable distribution of spiritus
in all
the muscles and unblock the vessels of which sleep or rest may have slowed

the functions”, and that their action fights “against the excessive pre-
eminence of the flexor muscles and returns everything to its place”. In
his
1755 book De perspiratione insensibili, Johan de Gorter [9] was the first
to
describe yawning as accelerating blood flow, supposedly to improve the
oxygenation of the brain, in response to cerebral anaemia. Well into the
20th
century, there were regular references to this notion, even though it had
never been demonstrated. Even someone as knowledgeable and inquisitive as
JM Charcot repeated this maxim without any critical analysis in his Leçons
du
Mardi à la Salpêtrière in 1888. The inaccuracy of this hypothesis was
formally
shown by Provine, Tate and Geldmacher in 1987 [10]. They had their
subjects
inhale air with higher than normal levels of CO2 (3-5% vs. <0.5%). In
response, the subjects’ breathing rates increased, but they did not yawn.
Likewise, when the subjects inhaled pure oxygen, there was no inhibition
of
spontaneous yawning at normal rates. Hence yawning is not a physiological

reflex to improve cerebral oxygenation.

Phylogenesis, ontogenesis, ethology

The existence of yawning in reptiles confirms the primitive
phylogenetic
origins of this behaviour. Its survival without any notable evolutionary
variations is an indication of its functional importance, as confirmed by
its
early ontogenetic manifestation. It coincides with the first type of sleep

involving hypotonia, which evolves towards REM sleep between weeks 12 and
15 of pregnancy [11]. Ethology supports the idea that almost vertebrates
yawn, whether heterotherms or homeotherms, whether herbivores,
frugivores, insectivores or carnivores, whether they inhabit water, land
or air.
Probably giraffes, whales and dolphins do not yawn; the physiology of
their
sleep is not completely understood. It seems that they be lacking of
durable
REM sleep and their sleep occurs in one by one hemisphere.

Physiology

Living organisms, particularly vertebrates, exhibit varied behaviours

which are essential to their survival and characterised by cyclical
recurrence.
This is the case for the three behaviours fundamental to life and its
transmission: alertness (ability to survive predators while still needing
to
sleep to maintain brain homeostasis), feeding (energy capture) and
sexuality
(perpetuating life). Yawning and pandiculation are morphologically
identical
and apparently associated with each transitional state of the infradian,
circadian and ultradian rhythms which characterise them. Rather than the
result of a passive adaptation to environmental conditions, an animal’s
behavioural transitions are dictated by internal stimuli characteristic of

homeostatic adaptations, generated in particular by the hypothalamus
(suprachiasmatic nuclei, paraventricular nuclei). These internal
biological
clocks permit a precise balancing act between metabolic needs (satiety),
survival of the species (copulation) and environmental conditions (tonic
adaptation to weight and movement). Yawning and pandiculation are
associated with transitions between wakefulness and sleep, occurring at
the
onset of hunger or satiety and with the ebb and flow of emotional states
secondary to living in hierarchical social groups [12].

Yawning and pandiculation exteriorise the activity of the motor
centres of
the brainstem (V, VII, IX, X, XI, XII) and of the spinal cord, under the
control of
the hypothalamic paraventricular nucleus (PVN). The PVN is a point of
integration between central and peripheral autonomic systems. Amongst
other things, it plays a role in metabolic balance (osmolarity, energy),
blood
pressure and heart rate, and sexuality. Yawning and pandiculation can be
triggered by injections (apomorphine, hypocretins, etc.) or inhibited
after
electrical lesion in the parvocellular zone of the PVN [13]. A group of
oxytocin
neurons situated in this zone and projecting to the hippocampus, the
brainstem (locus ceruleus) and the spinal cord control yawning and
erection.
The stimulation of these neurons by dopamine or its agonists, such as
excitatory amino acids (NMDA) and oxytocin itself, triggers yawning and
erection, whereas GABA and opioids have an inhibitory effect [14].

Current knowledge and beliefs about yawning

It is interesting to contrast current views of yawning held by
physicians in
France and India, and then compare them to beliefs amongst the general
French or Indian public. We compared the data gathered in 1998 in France,
partially published in a journal read by French family physicians [15],
and
those of the present study in India.

In all parts of the world, and regardless of the level of medical
knowledge, yawning is associated with the idea of tiredness, boredom, lack
of
sleep or non-restorative sleep. Due to their capacity to decode emotions
expressed by behaviour and facial expressions, humans add an additional
non-verbal meaning to the physiological role of yawning. In any culture, a

yawning person sends the signal that he or she is bored and expresses lack

of interest. Western culture associates an unfavourable connotation, a
lack of
respect, with this behaviour.

In France, women and men are considered to yawn equally often,
whereas in India, a larger proportion of the people questioned thought men

yawned more often than women, which is incorrect [16].

Curiously, 30% of the laypeople questioned in India doubted the
existence of yawning in animals. The French, known for their close
companionship with dogs and cats, did not have doubts about whether their
pets yawned, but rarely knew that birds and fish yawn as well. Oddly, many
of
them thought that their yawning could trigger yawning in their dogs. On
the
contrary, yawning induced by echokinesis has only been found in great apes

and humans, and appears to be species-specific. Modern neurophysiology
explains this phenomenon as activity in the right parietal-temporal
cortex,
comparable to that observed during empathy [17]. Echokinesis thus seems
impossible between canines and hominids. As such, anthropomorphism can
be seen in this popular French belief [18].

The French reported appreciating the brief pleasure associated with a

successful yawn. It is quite common for them to complain about
unsatisfactory yawning when they don’t experience the short period of
relaxation that follows, like a moment of ecstasy. Relaxation and yoga
techniques are well suited to bringing about this state of harmony [19].
Strangely, 28% of the Indian laypeople questioned did not experience this
sensation of well-being. 39% of them felt better after yawning, versus
only
19% of the physicians questioned. On the contrary, 43% of the physicians
reported they didn’t like to yawn, versus 19% of the laypeople questioned.

This paradox may be explained by the fact that the proportion reversed
itself
when participants were asked whether yawning could signal illness.

Regardless of the continent, only a small proportion of the general
public
believe medicine has the therapeutic means to reduce the frequency and
number of yawns, compared to a larger percentage of physicians (4% versus
27%). Studies have shown that coffee reduces the number of yawns, as do
neuroleptics, baclofen (GABAergic) and opioids.

Amongst both physicians and non-physicians, irrespective of culture,
it
is well known that women yawn more during pregnancy. This is explained by
progesterone’s modulation of D3 dopamine receptors in the PVN [20].
Indians also believe that breastfeeding women yawn more. This tendency is
clearly explained by the crucial role of oxytocin in triggering a yawn,
but the
French tend not to notice it, perhaps because French mothers have
regrettably
lost interest in breastfeeding [21].

Regardless of culture, the general public prefer chewing something
(ancestral practice advocated by Indian folk medicine) to try to avoid
exteriorising a yawn, whereas physicians prefer clenching their teeth.
Everyone knows that stretching or pandiculation favours yawning rather
than
preventing it.

In France, amongst physicians as well as laypeople, the notion that
yawning improves the supply of oxygen to the brain is widespread despite
its
inaccuracy, indicative of a belief without critical foundations, rather
than
validated scientific knowledge.

In France as in India, physicians still know little about yawning.
The most
conducive times for this behaviour – upon waking, before sleep and when
hungry – are known. Likewise, the association of yawning with vasovagal
events or hypoglycemia is relevant. Very few Indian or French
practitioners
evoke stimulation to explain the physiological role of yawning. There is
little
knowledge of iatrogenic causes, even though they most frequently explain
excessive yawning, linked to serotonergic antidepressants [22]. There is
little
awareness of fetal yawning, which can be observed with ultrasound, despite

the negative implications of its absence (delayed functional maturation in
the
brainstem, for example). Little is known about pathological yawning even
though it is frequent during migraines, and in sleep apnoea, temporal lobe

epilepsy, stroke, pituitary disorders, and in hyperactivity/attention
deficit
disorder.

Whether French or Indian, 100% of the physicians questioned said
yawning was never discussed during their medical studies. During this 8-
year
training period, less than 5 hours are devoted to sleep in France, and
only 2.5
hours in India, even though we spend a third of our lives sleeping.
Yawning,
a daily behaviour at every age, is not even considered!

The fact we know so little about this daily activity, which like any
physiological behaviour has its own pathology, and the fact this ignorance
is
equally as common amongst physicians and laypeople can only be met with
surprise. Moving away from folk knowledge, akin to believing in magic, and

towards scientific understanding might require integrating the study of
yawning into medical training.

References

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understanding of
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Competing interests:
None declared

Competing interests: No competing interests

03 February 2008
olivier walusinski
family physician in france
28160 Brou