The interactions between botulinum-toxin-based facial treatments and embodied emotions

Abstract

Botulinum toxin (BTX) injections reduce muscle mobility and are commonly used to treat the appearance of glabellar frown lines. Research shows that this cosmetic treatment leads to a reduction in depression. This reduction is consistent with the theory of embodied emotions because patients have a reduced ability to frown and so receive less negative feedback associated with this action. The current research explored this effect and three further hypotheses for the effects of cosmetic BTX injections based on embodied emotions. It was hypothesised that treatment of crow's feet (or laughter lines) would reduce mood as patients' Duchenne smiles would be impaired. It was hypothesised that facial BTX treatments would impair emotional expression recognition because the ability to mimic emotions would be reduced. Finally, it was hypothesised that, as BTX treatments prevent facial expressions associated with sexual excitement, sexual function would be impaired after treatment. Twenty four BTX-treated and twelve matched participants (all female) were tested before and after treatment. Results found that BTX treatment of laughter lines was associated with increased depression scores. Further, BTX treatment was associated with reduced emotion recognition ability and sexual function. The current results add to our knowledge of the psychological effects of injections of powerful neurotoxins and broaden the scope of the embodiment of emotions.

Full text

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Scientific REPORTS | (2018) 8:14720 | DOI:10.1038/s41598-018-33119-1
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The interactions between
botulinum-toxin-based facial
treatments and embodied
emotions
Michael B. Lewis
Botulinum toxin (BTX) injections reduce muscle mobility and are commonly used to treat the
appearance of glabellar frown lines. Research shows that this cosmetic treatment leads to a reduction
in depression. This reduction is consistent with the theory of embodied emotions because patients have
a reduced ability to frown and so receive less negative feedback associated with this action. The current
research explored this eect and three further hypotheses for the eects of cosmetic BTX injections
based on embodied emotions. It was hypothesised that treatment of crow’s feet (or laughter lines)
would reduce mood as patients’ Duchenne smiles would be impaired. It was hypothesised that facial
BTX treatments would impair emotional expression recognition because the ability to mimic emotions
would be reduced. Finally, it was hypothesised that, as BTX treatments prevent facial expressions
associated with sexual excitement, sexual function would be impaired after treatment. Twenty four
BTX-treated and twelve matched participants (all female) were tested before and after treatment.
Results found that BTX treatment of laughter lines was associated with increased depression scores.
Further, BTX treatment was associated with reduced emotion recognition ability and sexual function.
The current results add to our knowledge of the psychological eects of injections of powerful
neurotoxins and broaden the scope of the embodiment of emotions.
e reduction of facial wrinkles using injections of botulinum toxin (BTX) has become a staple of the aesthetic
treatment industry. It is the most popular cosmetic procedure with 4.5 million treatments during 2016 in the
USA1. e pharmacological action of BTX is to reduce the mobility of the targeted facial muscles, which con-
sequentially reduces the appearance of facial lines2. ere is increasing evidence, however, that these treatments
aect the patients’ psychological responses as well as just their muscular actions and appearance of lines. Here, the
eects of cosmetic BTX treatments on these psychological responses are considered together with explanations
for these ndings based on the concept of embodied-emotions. Further hypotheses, in three areas of interest, are
derived from the theory of embodied emotions and these are tested in a group of BTX-treated patients and com-
parison patients. e rst area of interest is the eect of BTX treatments on the muscles used to express positive
and negative emotions and how these may have negative and positive eects on mood respectively. e second
area of interest is how BTX treatments may prevent facial mimicry and whether this might impair emotion recog-
nition. e nal area of interest considers the role that facial expressions play during sexual excitement and how
BTX treatments might reduce these expressions and hence potentially sexual satisfaction.
e most studied psychological eect of BTX treatments has been the change of mood that results from the
treatment of frown lines. It was originally observed that patients treated for glabellar lines with BTX appeared to
be happier3. is observation could have been in appearance only as these patients had a reduced ability to frown
even if they were unhappy; however, it has since been shown that this eect on mood goes beyond just the appear-
ance. Finzi & Wasserman4 demonstrated that the treatment of frown lines reduced signicantly the symptoms of
patients with depression and Lewis & Bowler5 demonstrated that there is a general improvement in mood follow-
ing BTX treatment for frown lines compared to a comparison group who had received other cosmetic treatments.
Since these studies, there have been a number of randomised control trials (RCTs) demonstrating the robust eect
that BTX treatment of frown lines has on depression6–11.
School of Psychology, Cardi University, Cardi, CF10 3AT, UK. Correspondence and requests for materials should
be addressed to M.B.L. (email: LewisMB@Cardi.ac.uk)
Received: 2 May 2018
Accepted: 4 September 2018
Published: xx xx xxxx
OPEN
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e common explanation for the eect that BTX has on mood derives from the facial feedback hypothe-
sis12. is theory suggests that forming a facial expression strengthens the internal feeling of that expression.
Demonstrations of this eect include that smiling causes a cartoon to seem funnier13. Although there has been a
challenge to this original nding14, there have been many replications of the principle and a meta-analysis shows
a robust facial-feedback eect15. A range of emotions have also been shown to be aected by feedback from
facial expressions: wrinkling one’s nose makes one more disgusted16 and frowning leads to pictures being more
negatively evaluated17. Emotional feedback is not restricted to facial actions and explorations of the eects that
moving one’s body, as well as one’s face, has on emotions has led to the idea of embodied emotion18,19. Embodied
emotion provides a possible explanation for the eect BTX treatments have on mood: patients who have received
treatment for corrugator and procerus muscles (muscle groups targeted in frown line treatments) would be una-
ble to frown and so would not receive the negative aective feedback that is the embodied emotion associated
with frowning. e explanation is that the lack of feedback of negative aect leads to the positive eect that BTX
treatments have been shown to have on mood.
Embodied emotions and the facial feedback hypothesis were developed under the prevailing view of the basic
emotion theory that suggests that emotional expressions are the outward signals of inner feelings20. However,
more recent work suggests that facial expressions are tools for social inuence and the links between emotions
and facial expressions may not be as direct as previously thought21,22. e alternative behavioral ecology view
of facial displays suggests that frowning may not always indicate sadness or anger but might instead be used
to recruit protection or elicit submission. On this view, emotions do not always feedforward to facial displays.
Embodied emotions and facial feedback can be seen as being potentially consistent with both views of emotional
expressions because regardless of whether a frown is originated from a feeling of sadness or an attempt to recruit
protection, the theory of embodied emotion predicts that frowning increases sadness. So while there may or may
not be feedforward of emotions to expression, there is evidence, as stated above, that expressions feedback to
emotions.
It could be argued that an alternative explanation for the BTX eect on mood based on social interactions.
e BTX treatment prevents frowning and so the person is less likely to frown at the people around them. Due to
the social mimicry of emotional expressions, this means that fewer people will frown back at the person, which
could have an overall positive eect on mood. While this alternative explanation is possible, evidence against it
comes from the demonstration that BTX treatments aect the activation of the amygdala during a facial mimicry
exercise23 and so even outside of a social context, BTX is aecting the processing of emotions.
Until now, cosmetic BTX treatments have been shown to have largely positive eects on a person’s mood.
Here, the possibility is explored that these treatments may also have negative eects as directly predicted from the
ideas of embodied emotions.
Laughter Lines
Frown lines are not the only facial lines that are commonly treated using cosmetic BTX injections. Lines radiating
from the corners of the eyes are oen targeted through injections into the orbicularis oculi muscles24. ese lines
are known as crow’s feet or laughter lines and research reported here explores whether pharmacological paralysis
of the muscles producing these laughter lines has any eect on mood.
The orbicularis oculi muscles play an important role in smiling as demonstrated by research into the
Duchenne smile25. A Duchenne smile (or true smile) is one that involves both the mouth and the eyes: the zygo-
maticus major and the orbicularis oculi muscles are contracted. is can be contrasted with a false smile, which
only employs the zygomaticus major and is sometimes referred to as a Pan Am smile or a Botox smile26. Research
shows that a smile expression using the eye muscles is seen as being warmer and more sincere than one that uses
only the mouth muscles27. Soussigan28 demonstrated that the facial feedback eect from smiling is stronger when
the orbicularis oculi muscles are contracted. e potential importance of Duchenne smiles have also been shown
in two studies of photographs in yearbooks. ese studies showed that people who showed a Duchenne smile in
their yearbook divorced less29 and lived longer30 than those that only smiled only with their mouths. Exactly why
these relationships exist is unclear but these studies show that people who tend to smile with their eyes have more
positive life outcomes.
Given the importance of the orbicularis oculi muscles in smiling, it would be expected that reducing their
mobility by using BTX injections will have psychological consequences. e theory of embodied emotion pre-
dicts that reducing a person’s ability to make a Duchenne smile would reduce the facial feedback they receive
from a smile. A possible consequence is that a person’s mood will be lower if they have received a BTX treatment
that reduces the mobility of their orbicularis oculi muscles. e BTX treatment of crow’s feet does exactly that.
One aim of the current study was to explore the eect of BTX treatment of crow’s feet on mood scores before
and aer treatment. Participants were recruited that either received BTX for just their frown lines or received
BTX for both frown lines and crow’s feet – it is unusual to nd people who have had crow’s feet treated but not
frown lines. e hypothesis was that those people who had received BTX treatment for crow’s feet would score
higher on a measure of depression aer treatment than those who received a dierent treatment.
Emotion Recognition
Embodied emotion has been shown to aect the recognition of emotional expressions in others and this is
explained through the eect of mimicry. Evidence for this is that the recognition of the emotions in other people
is improved with facial mimicry31. Indeed, preventing mimicry of emotional expressions leads to poorer emotion
recognition32, whereas encouraging expression mimicry can increase emotion recognition accuracy33. It would
be expected, therefore, that treatments that reduce the ability to mimic facial expressions of others would lead to
reduced accuracy in determining the emotions portrayed in the facial expressions of others.
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Research already exists that explores the eects of BTX injections on emotion processing. For example, the
time it takes to read an emotional text is lengthened following facial BTX injections34. Also, the size of the emo-
tional response to video clips is reduced for BTX treated participants compared with controls35. is indicates
a reduction in felt emotion, which is conrmed by lower activation in the amygdala when BTX-treated people
attempt to mimic an angry expression23. Baumeister, Papa & Foroni36 tested people who had been treated with
BTX for frown lines and matched controls. ey found that, compared to controls, BTX treated participants rated
slightly emotional sentences as being less emotional. Similarly they found that happy and sad faces were rated
as less happy and less sad respectively by the BTX treated group. Finally, happy and sad faces were categorised
as such more slowly aer the BTX treatment. ese studies, together, suggest that there is reduced emotional
responding following BTX treatment.
is previous research demonstrates that the strength of an emotional evaluation is reduced or slowed fol-
lowing BTX treatments. What is potentially more interesting is whether there is also a reduction in the accuracy
with which emotional expressions are recognised. BTX injections for cosmetics reasons lead to a reduction in
the ability to mimic certain facial expressions. erefore, as mimicry is important for emotional expression rec-
ognition, one would expect to nd that people who have had cosmetic BTX treatments to be poorer at emotion
recognition tasks. Previous research has found that BTX treatment does reduce the ability to determine emotions
when expressed in just the eyes37 using e Reading the Mind in the Eyes task (RMET)38.
The current research builds on this previous research in two ways. First, participants were tested
before and after treatments using a prospective design to isolate individual differences. Second, a full-face
emotion-recognition task was included, as well as the RMET, in order to assess more natural viewing. is second
task was the facial expression recognition (FER) test39 which consists of the Ekman faces40 blended with neutral
faces to vary the diculty of the task, which is to judge the emotion being shown on the face. It was hypothesized
that those who received BTX treatments would show a decit in emotion recognition tasks following treatment
and further this detriment would be greater than that observed in a comparison group who received a cosmetic
treatment that did not involve BTX.
Sexual Pleasure
e current research also explored whether embodied emotion or facial feedback have a role to play in sexual
intercourse and successful orgasm. Orgasmic dysfunction has a prevalence rate of between 16–25% for women41
and is related to sexual satisfaction. Indeed, the female orgasm has received considerable research interest since
the late twentieth century42. e role of facial expressions during intercourse is considered here and whether
treatments that reduce facial expressions of emotion can impact upon the quality or ease of achieving orgasm.
Only a few studies have looked at facial expressions during sexual intercourse but what research there is sug-
gests that there are consistent involuntary facial actions associated with orgasm. Famously, Master and Johnson43
studied behaviour during 10,000 sexual interactions. One of their many observations was the common occur-
rence of frowns seen during the plateau phase (that is the sexual excitement prior to orgasm). e presence of
frowning during sexual excitement was further conrmed by researchers44 who coded video clips of people’s faces
during masturbation using the Facial Action Coding system45. e largest dierences in expressions between the
plateau stage and either the initial baseline or the resolution stages were for the presence of jaw drop (AU26) and
frowning (AU4). Popular culture has coined the term the ‘O face’ to refer to this expression46.
Studies of non-human primates have also found consistent patterns of facial expressions during sexual excite-
ment. Stump-tailed macaque demonstrate contraction of the corrugator (or frown) muscles during sexual activ-
ity47,48. While this nding is suggestive of there being a potential universality to this facial expression, recent
research has found some slight cultural variations in the facial expressions produced during sexual pleasure49.
ere are several reasons for the facial expressions associated with orgasm. First, it could be that the facial
expressions improve coital communication providing feedback to the sexual partner. is is consistent with the
behavioural ecology view of emotional expression22. is communication may act as a reward to the partner
or just improve timing and cooperation – either way; this would act to enhance pair bonding. Alternatively,
applying embodied emotion to the experience of sexual excitement suggests that the act of frowning is not just a
response to sexual excitement but may also support and enhance it. at is, the O face is not just a result of sexual
excitement, but it is part of the experience of sexual excitement without which the experience will be reduced. A
consequence of this latter explanation is that inhibiting the facial expression of arousal, either through volition
or pharmacologically, would reduce the experience of that arousal. e hypothesis tested here, therefore, is that
participants’ reports of sexual pleasure will be reduced following BTX injections that prevent the frowning that is
associated with sexual excitement.
In order to test the eect of BTX cosmetic treatment on sexual pleasure, the quality of participants’ sexual
experience was measured using the Female Sexual Function Index (FSFI)50. is measure consists of 19 questions
that relate to the six domains of sexual function: desire, arousal, lubrication, orgasm, satisfaction and pain. While
the hypothesis suggests that BTX treatment will have a detrimental eect on sexual function as a whole, it was
also predicted that the domain of orgasm would be aected most by BTX treatments.
Experiment
The current experiment compared participants who received BTX cosmetic treatment with those who had
received cosmetic treatments that do not aect facial mobility. As people self-selected their treatment, this would
be better called a quasi-experiment rather than an experiment. Comparisons were also made between partici-
pants who received BTX treatment for frown lines only and those that combined that treatment with BTX treat-
ment for crow’s feet and so there were three groups of participants. e design was naturalistic with participants
being recruited who were undergoing self-selected cosmetic treatment but participants were tested prior to the
cosmetic treatment and following their treatment to compare each participant with their own baseline measures.
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Although there were no gender-based selection criteria, all participants were female. e quasi-experiment
explored the participants’ mood, their ability to recognise emotional expressions accurately and it included a
measure of sexual function.
Results
Participant Categorisation. Twenty four of the thirty six participants (all female) reported receiving BTX
injections between the rst testing session and the second testing session. ese injections were to the corrugator
and procerus muscles to treat glabellar frown lines. Of these participants, 11 also had further injections into their
orbicularis oculi muscles to treat crow’s feet. e comparison group were 12 female participants who had no BTX
injections but did receive facial peels, dermal llers, laser treatment or dermal needling between the rst session
and the second session. Table1 provides demographic details of the three groups of participants and details of the
timing of the two sessions. e ages of the participants were not signicantly dierent between the three groups,
F(2, 33) = 1.804, p = 0.180. All participants were asked to complete all parts of the procedure on two occasions.
Two participants (both in the BTX frown line only condition) choose not to complete the FSFI questionnaire in
either session.
Mood Questionnaire. e scores on the Hospital Anxiety and Depression Scale (HADS)51 questionnaire
show that there was a decrease in negative mood following treatment for the participants who received the BTX
treatment for frown lines only whereas a similar decrease was not seen for the non-BTX group nor the BTX frown
lines and crow’s feet group (Fig.1). A two-way ANOVA with factors of treatment type and session found a signi-
cant interaction, F(2, 33) = 8.564, p = 0.001, η2 = 0.318. Using planned comparisons, it was revealed that there was
a signicant improvement in mood (lower HADS scores) for participants who had received BTX treatments for
frown lines only, t(12) = 3.285, p = 0.007, d = 1.897, whereas the HADS score were higher, albeit non-signicantly,
for the participants who had received BTX treatment for crow’s feet as well, t(10) = 0.339, p = 0.742, d = 0.214,
and for those who were in the non-BTX group, t(11) = 1.201, p = 0.255, d = 0.724.
The overall HADS score could be split according to a depression element and an anxiety element. A
three-way ANOVA including the measure as a factor (depression versus anxiety) found a non-significant
Comparison
Group. Non-
BTX BTX frown
lines only
BTX frown
lines and
crow’s feet
N 12 13 11
Average Age 38.8 43.9 45.6
(Range) 28–54 32–65 31–55
Ethnicity:
White 11 13 11
Mixed 1
Average time between rst session
and treatment. 8.1 days 9.5 days 6.3 days
Average time between treatment
and second session. 36.8 days 40.2 days 41.8 days
Table 1. Demographic details for the 36 participants. ese are split according to what BTX treatments they
received.
Figure 1. Baseline and post treatment average scores on the HADS mood questionnaire. Participants are
categorised according to what type of BTX treatment they received. Error bars show 95% condence intervals.
Signicance values show the simple comparisons before and aer treatment.
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treatment-by-session-by-measure interaction, F(2, 33) = 0.017, p = 0.986, η2 = 0.001. Alternatively two separate
analyses of the two measures found signicant interactions between session and treatment type for both anxiety,
F(2, 33) = 5.393, p = 0.009, η2 = 0.246, and depression, F(2, 33) = 4.980, p = 0.013, η2 = 0.232.
Reading the Mind in the Eyes test. The responses to the test of emotion recognition based on eye
regions only for the 36 images were converted into a single measure of accuracy in terms of proportion correct.
Figure2 shows the overall performance on this test before and aer treatment for the two BTX treated groups
and non-BTX treated groups. A two-way ANOVA with factors of treatment type and session found an interaction
that approached signicance, F(2, 33) = 3.78, p = 0.050, η2 = 0.116. is interaction was signicant, however, if
the two BTX conditions were contrasted against the non-BTX condition, F(1, 34) = 4.578, p = 0.040, η2 = 0.095.
Using planned comparisons, it was revealed that there was a signicant drop in performance following BTX
frown line treatment, t(12) = 2.277, p = 0.042, d = 1.314, and following BTX frown line and crow’s feet treatment,
t(10) = 2.399, p = 0.037, d = 1.517, but not following non-BTX treatments, t(11) = 0.810, p = 0.435, d = 0.488.
Facial Emotion Recognition test. e FER test was analysed to obtain a measure of overall accuracy of
emotion identication regardless of the strength of the emotion being expressed. Figure3 shows the performance
on this test for the participants before and aer treatment. e accuracy measure increased aer treatment for
non-BTX treated participants but decreased for BTX-treated participants. A two-way ANOVA with factors of
treatment type and session found a signicant interaction, F(2, 33) = 4.375, p = 0.021, η2 = 0.210. Using planned
comparisons, it was revealed that there was was a signicant rise in performance for non-BTX treated partici-
pants, t(11) = 2.321, p = 0.040, d = 1.400, whereas the fall in performance was not signicant for the BTX frown
line treated participants, t(12) = 0.820, p = 0.420, d = 0.473, but was signicant the BTX frown line and crow’s feet
treated participants, t(10) = 2.543, p = 0.029, d = 1.608.
Female Sexual Function Index. Figure4 shows the pre-treatment and post-treatment scores on the
orgasm component of the FSFI for the two BTX-treated groups and non-BTX-treated group. e BTX-treated
groups show a drop in the overall orgasm satisfaction score aer treatment regardless of whether the crow’s feet
were treated or not – a drop that was not apparent in the non-BTX group. An ANOVA was carried out with fac-
tors of session (baseline or post-treatment) and treatment type on the orgasm satisfaction score. e interaction
Figure 2. Baseline and post treatment average performance on the Reading the Mind in the Eyes test.
Participants are categorised according to what type of BTX treatment they received. Error bars show 95%
condence intervals. Signicance values show the simple comparisons before and aer treatment.
Figure 3. Baseline and post treatment average performance on the Facial Expression Recognition (FER) test.
Participants are categorised according to what type of BTX treatment they received. Error bars show 95%
condence intervals. Signicance values show the simple comparisons before and aer treatment.
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between treatment type and session was signicant with scores dropping more following BTX treatments than
non-BTX treatments, F(2, 31) = 3.650, p = 0.038, η2 = 0.191. Using planned comparisons, it was revealed that
there was no signicant change for the non-BTX participants, t(11) = 0.638, p = 0.536, d = 0.385, but there
was a signicant drop in FSFI following treatment for BTX-treated frown-line only participants, t(10) = 3.012,
p = 0.013, d = 1.905, and an near signicant drop following treatment for BTX-treated frown-line-and-crow’s-feet
participants, t(10) = 2.508, p = 0.067, d = 1.596. e full FSFI dataset (with all six subscales) is available for anal-
ysis at https://osf.io/qx4pa/.
Discussion
Botulinum toxin is a powerful neurotoxin. Its eects on targeted muscle groups are eective for a wide range of
medical conditions and it has rapidly become a popular cosmetic treatment product1. e current study demon-
strates that the use of BTX for its cosmetic eects can have wide reaching psychological eects as well. e results
inform us of these potential psychological eects but it also tells us more about the embodiment of emotions18.
e results reported here demonstrate that BTX treatment for glabellar frown lines leads to an improved mood
in cosmetic patients, which supports for previous ndings5. Unlike earlier research, the mood-improving eect
of BTX was found here within participants (rather than between participants) using a baseline/post-treatment
design. is conrms that the participants’ mood was changing aer treatment rather than just happier peo-
ple being more inclined to select BTX treatments. is is also supported by the RCT that have been carried
out recently on its eectiveness as a treatment for depression6–11. e current nding is also consistent with the
embodied-emotion based idea that interrupting the ability to frown reduces negative aect.
e current research explored mood further by looking at the eect that BTX treatment of crow’s feet has on
mood. is treatment involves injections into the orbicularis oculi muscles and leads to a reduction in facial lines
that are sometimes called laughter lines. Based on embodied emotion18, it was predicted that treating the laughter
lines would lead to a lowering of a person’s mood. It happened that all of the participants who were BTX treated
for crow’s feet were also BTX treated for frown lines. As such, in order to isolate any eect of treating crow’s feet, it
makes sense to contrast those people who received BTX for frown lines only with those people who received the
treatment for both frown lines and crow’s feet. e results of this comparison showed that the eect of having had
a treatment for crow’s feet was to increase depression and anxiety scores relative to those who had only received
the frown lines treatment.
e theory explaining why treating crow’s feet lowers mood is the same as that explaining why treatment
of glabellar frown lines improves mood. Treatment of crow’s feet using BTX injections in the orbicularis oculi
muscles leads to a lack of mobility in those muscles and the inability to smile using the eye muscles, that is, make
a Duchenne smile. e strength of the facial feedback that a person would get when smiling would therefore be
reduced relative to an untreated person and hence they feel less happy even when smiling. e current results
show that the size of the negative eect of treating the crow’s feet appears to be similar in size to the positive eect
of treating the frown lines and so for people having both treatments there is no net drop in mood. is nding
demonstrates the potential for negative consequences of interfering with the embodiment of emotions. It is also
an important consideration for anyone who is tempted to have only their laughter lines treated with BTX as this
may lead to an increase in depression scores.
e second hypothesis tested was that a loss of mobility in the face as a result of BTX injections would be
related to a loss in emotional-expression recognition ability, testing the concept that facial mimicry is impor-
tant in emotional expression decoding. is eect had been shown previously but in an experiment that only
assessed emotion recognition from the eye region37 and so it remained unclear as to whether whole face emotion
recognition would be similarly aected. Two separate measures of emotion recognition were employed in the
current quasi-experiment. e RMET conrmed the previous nding that emotion recognition from the eyes was
aected by BTX injections. is research was extended by the nding that emotion recognition from the whole
face was similarly aected by BTX injections as observed in the FER task.
e current ndings from the FER and RMET are taken as evidence that the BTX treatment is interfering with
the emotion-recognition pathways. e assumed pathway in question is the process of mimicking the expression
being judged in order to better feel the emotion being expressed31. By preventing or reducing this mimicking
Figure 4. Baseline and post treatment scores on the orgasm subscales of the Female Sexual Function Index
(FSFI) categorised according to what type of BTX treatment they received. Error bars show 95% condence
intervals. Signicance values show the simple comparisons before and aer treatment.
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process, the BTX treatment is reducing the accuracy with which facial expressions of emotion are recognised. e
consequence of this eect is that people who have undergone BTX cosmetic treatment may be less able to interact
eectively in social settings that might require interpretation of subtle facial cues.
Another question is whether people who have more BTX treatment show a greater detriment in
emotional-expression recognition than those who have less BTX treatments. From the evidence collected here,
both the FER test and the RMET show a larger detriment in emotional expression processing following treatment
for crow’s feet and frown lines than for just frown lines. Care must be taken when interpreting this potential
eect as it is possible it may be inuenced by the dierent baseline abilities in the FER test. While the dierences
between the two BTX conditions in each task are non-signicant, their combined eect is suggestive of the eect
that people with frown lines and crow’s feet treated with BTX show a larger detriment in emotional-expression
recognition than those who only have their frown lines treated. Fully evaluating this dierence will require fur-
ther research dedicated to answering this question, in particular assessing the total number of units of BTX
received as well as the number of locations treated.
e nal and most novel hypothesis that was tested concerned the expression of pleasure during sexual excite-
ment. Previous research has shown that the muscle groups oen targeted in cosmetic BTX treatments are the
same ones that are associated with sexual excitement and orgasm44. Reduction of mobility of these muscles may
therefore interfere with the expression and feedback of excitement during sexual activity. e current research
provides support for this hypothesis in that participants reported that, following BTX treatment, there was a
decrease in sexual function: in particular, orgasms were harder to achieve and were less satisfying.
e current study suggests that reducing the ability to make the facial expressions associated with sexual
pleasure leads to a reduction in the reported feeling of pleasure associated with it. is nding demonstrates the
importance of facial expressions during sexual intercourse. e results suggest that the facial expressions do not
occur simply to communicate pleasure to a partner but they are an integral part of the feeling of pleasure and are
important in the process of achieving orgasm. is demonstrates an important role for facial feedback within
sexual intercourse and it is potentially a previously unimagined signicant negative impact from cosmetic BTX
treatments.
e current research only used self-report measures for analysing the eect of BTX treatments on sexual
function. Given that the facial expressions during intercourse may have more than one role, future research
should look at the wider eects that the treatment may have. In particular, it has been hypothesised that the
female orgasm is part of pair-bonding52 and so communication of the orgasm through facial expressions will be
an important aspect of emotional closeness. As such, future studies should look at the experience and satisfaction
of the sexual partner of the person who has received the BTX treatment to investigate whether the loss of the
communication element of the O face leads to a reduction in either their satisfaction or their emotional closeness.
A limitation of all parts of the current study is that the participants self-selected for the treatments that they
received. is means that the ndings do not reach the gold standard of a RCT. e justication for the current
methodology is that it would not have been ethically acceptable to carry out this study as a RCT to test the current
hypotheses because these propose that the BTX-treatments have negative eects, albeit in very specic domains.
It would not be ethical to randomly give a proportion of the participants a treatment that may make them sad,
make it dicult for them in social settings or reduce their sexual satisfaction. It is ethical, however, to study
people as they do this to themselves anyway in their attempts to look younger. In spite of this limitation, the fact
that the participants were tested before and aer treatment and the treatments were compared with other similar
treatments means that the research is superior to some earlier demonstrations of the psychological eects of BTX
treatments.
A further limitation of the study was the lack of any male participants, which therefore limits any conclusions
to a female population. ere are no strong reasons why mood or emotion recognition might be dierentially
aected by BTX treatments in men than in women and so one might expect the eects to generalise to males
but this remains unknown. As currently over 90% of cosmetic BTX treatments are administered to women1, it
remains useful to gain an insight into how these treatments are aecting just this group. e ndings regarding
orgasm are particularly dicult to generalise from female to male as orgasms are dierent between the two
sexes52. However, the corrugator muscle has been shown to be involved in the male orgasm as much as the female
orgasm44 and so one would predict that the BTX-treatment eect would occur for males as well as females.
In conclusion, the current research used a prospective baseline/retest design with participants undergoing
cosmetic treatments in order to assess the psychological eects of BTX treatments. e ndings represent a sig-
nicant addition to our knowledge concerning the impact of BTX cosmetic treatments. Equally, the ndings
make a signicant contribution to the theory of embodied emotions demonstrating its importance in a previously
untested domain of life. Specically, it is demonstrated that targeted injections of BTX into facial muscles can
aect a person’s mood in both positive and negative directions by treating either frown lines or laughter lines
respectively. Further, a person’s social interactions can be negatively aected by these injections both generally, in
terms of emotion recognition, and specically in terms of sexual pleasure. Although this is a relatively small scale
study, and further larger scale research is required, the sizes of these eects suggest that these powerful neurotox-
ins can have equally powerful psychological eects and consideration of these psychological eects is import for
both practitioners and patients in the cosmetic treatment industry.
Method
Power calculation. Previous research has demonstrated that the eects of BTX, where present, can be large
in size. An eect size of d = 1.410 has been found for depression5 whereas an eect size of d = 0.760 has been
found for emotional expression recognition37. ese estimates are based on between-participant analyses where
no baseline was taken. e power of the current study was enhanced by using a within-participant design testing
people before and aer receiving cosmetic treatment. In this kind of design the eect size on depression has been
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Scientific REPORTS | (2018) 8:14720 | DOI:10.1038/s41598-018-33119-1
shown to go up to d = 2.3211 and on emotion processing to be at d = 1.2236. Given this previous research, it was
calculated that at least ten participants per group would provide sucient power (α = 0.05, β = 0.80) to test the
emotion recognition hypothesis and fewer still to test the depression hypothesis. A power calculation was not
possible for the sexual function hypothesis and so this part of the research must be considered exploratory.
Participants. irty six participants were recruited through social media, newspaper adverts, snowballing
and local cosmetic clinics. All participants were female although the study was open to both males and females.
ese participants were planning on having some form of cosmetic treatment within the next month. is
quasi-experiment was naturalistic in design with the participants selecting their own treatment. An exclusion cri-
terion was having had a BTX cosmetic procedure within the last 12 months. Participants were tested once before
their chosen cosmetic treatment and once at least a month aer their treatment.
Procedure. Participants took part in two identical testing sessions. e rst of these sessions was at least 12
months since their last BTX cosmetic treatment and between 1 day and 1 month prior to undergoing a cosmetic
treatment. e second of these sessions took place between 4 weeks and 8 weeks aer treatment. e sessions
began with a questionnaire about the cosmetic treatments that had been received or that they were planning to
have. e remainder of the procedure consisted of a series of tests to assess mood, emotional expression recogni-
tion and sexual function.
e study was reviewed and approved for ethics by the Cardi University, School of Psychology Research
Ethics Committee and adhered to the ethical guidelines of the British Psychological Society. Informed consent
was obtained from all participants. e data collected are available for inspection at https://osf.io/qx4pa/.
Mood questionnaire. Participants completed the Hospital Anxiety and Depression Scale (HADS)51. is consists
of 14 questions with four alternative answers each. e answers of these questions were combined to provide a
single value depicting the level of mood (higher values showing lower mood).
Reading the Mind in the Eyes test. is test was developed as a measure of emotion expression processing to be
used with adults with autism38. Participants saw a series of 36 faces cropped such that only the eye region was
visible. e participants’ task for each image was to select from a list of four possible emotions which emotion
was the correct one being portrayed by the face. Participants could study the face for as long as they liked and the
next trial began once a selection had been made. e task started with a practice item that was not included in
the analysis.
Facial Emotion Recognition test. Six of the Ekman faces were used showing the emotions of happiness, sadness,
surprise, fear, anger and disgust. ese were morphed with the neutral version of the face to generate 4 levels of
intensity of each expression: 100%, 75%, 50% and 25%39. e participants saw each of the 144 faces individually
and responded as to which emotion was being presented (happiness, sadness, surprise, fear, anger, disgust or
neutral). Participants could study each face for as long as they liked and the next trial began once a selection had
been made.
Female Sexual Function Index. Participants completed the FSFI50. is consists of 19 questions about various
aspects of sexual experience from desire to satisfaction. Answers were scored from 1 to 5 (lower numbers indi-
cating lower sexual function) or they could record 0 if there had been no sexual activity. From these questions, an
overall measure of sexual function was calculated.
Design. e design was a baseline/retest evaluation of naturally observed cosmetic treatments. At retest,
participants were categorised into one of three groups depending on the cosmetic treatment they had received
between baseline and retesting (BTX frown lines only, BTX frown lines and crow’s feet or non-BTX). e main
dependent variables were the changes in performance from baseline to retest on the questionnaires (HADS and
FSFI) and emotion recognition tests (RMET and FER).
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Author Contributions
M.B.L. designed and carried out the experiments and was wholly responsible for preparation of the manuscript.
Additional Information
Competing Interests: e author declares no competing interests.
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