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The biology of BDSM: a systematic review
Elise Wuyts, Manuel Morrens
Abstract:
Introduction
BDSM is an abbreviation used to reference the concepts of bondage and discipline, dominance
and submission, sadism and masochism, enacted by power exchanges between consensual
partners. In recent years, attention has shifted from the idea of BDSM as a pathological and
tabooed niche practice towards viewing BDSM as a healthy form of intimacy.
Aim
This systematic review brings together all existing literature on the biology of BDSM and places
it in a broader biological context.
Method
A systematic search was conducted on Pubmed, Web of Science and PsycARTICLES, of which
ten articles are included and discussed in this systematic review.
Results
There is evidence for cortisol changes in submissives as a result of a BDSM interaction,
suggesting involvement of the physiological stress system. Endocannabinoid changes implicate
the pleasure and reward system. In dominants, this biologically measured pleasure seemed to
be dependent on power play rather than pain play. Testosterone and oxytocin are also implicated
in BDSM, though their role is less evident. Research into brain region activity patterns related
to BDSM interest suggests a role for the parietal operculum and ventral striatum in the context
of the pleasure and reward system, the primary and secondary somatosensory cortex in the
context of pain perception, empathy-related circuits such as the anterior insula (AI), anterior
midcingulate cortex (ACC) and sensorimotor cortex and the left frontal cortex in the context of
social and sexual interactions. Pain thresholds are shown to be higher in submissive individuals
and a BDSM interaction may cause pain thresholds to rise in submissives as well.
Conclusion
BDSM interactions are complex and influenced by several psychological, social and biological
processes. Though research is limited, there is emerging evidence for an interaction between
several biological systems involved in these types of interests and activities. This means there
is an important role for future research to replicate and supplement current results.
Keywords:
BDSM; sexuality; submissive; biological assessment; pain threshold; functional brain imaging
Introduction
BDSM is an acronym used to describe the concepts of bondage & discipline, dominance &
submission and sadism & masochism. It encompasses the psychological and physical roleplay
between two or more consenting partners, often involving a power exchange [1] between a
submissive party, (also referred to as “bottom” or “masochist”) and a dominant party (also
referred to as “top” or “sadist”). These interactions will often revolve around elements of pain
and power imbalance [2]. The BDSM practices referenced in this review all meet the
fundamental principle of safe, sane and consensual, which is a widely accepted cornerstone of
the BDSM community [3]. Coercive sexual sadism (i.e. sadistic practices with a non-consenting
partner) by its very definition is very different to consensual BDSM, even though certain
behaviour might seem similar on the surface [4]. Consequently, studies focusing on coercive
sexual sadism fall outside the scope of this review. For an overview of the current literature on
coercive sexual sadism, we refer to the systematic review of Mokros and colleagues [4].
In recent years, attention has shifted from the idea of BDSM as a pathological and tabooed
niche practice towards viewing BDSM as a healthy form of intimacy [5]. BDSM has shown to
be quite prevalent in society, with a large-scale survey study conducted by our group indicating
that 46.8% of the Flemish population had engaged in a BDSM-related activity at least once [6].
In the same study population, 7.8% identified as BDSM practitioners. Of these, 85.9% solely
practices at home, while 14.1% will also perform in a public setting. The practitioners identified
as follows: 28% as dominant, 36% as submissive, 27% as switch (i.e. persons who switch
between the dominant and submissive role) and 9% as other. Although more people are
becoming aware of what BDSM is and what it entails, much about the underlying psychological
and especially biological processes driving these interests and fantasies have yet to be revealed.
Are certain baseline biological processes related to an interest in BDSM? Do BDSM
interactions trigger biological changes that reinforce these interests? What changes might we
expect during a BDSM-themed interaction or “play” and how do these changes explain what
BDSM practitioners report?
We will begin by exploring several known aspects of the BDSM interaction and their biological
basis.
Pleasure and reward
Pleasure is an integral part of the BDSM interaction, and can be experienced in different ways.
Practitioners often refer to “sub-space” and “dom-space” as the euphoric state induced by a
BDSM interaction [7]. These subjective interpretations suggest an involvement of the pleasure
and reward system in the brain.
Experiencing pleasure is related to the activity of the reward system in the brain, with at its core
dopaminergic projections from the ventral tegmental area (VTA) to the nucleus accumbens
(NA), which are also mediated by opioid receptors [8]. Regulatory brain networks
implementing regions such as frontal cortical areas (orbitofrontal cortex, anterior cingulate
cortex,…) and limbic structures (hippocampus, amygdala), will regulate our behaviour and
result in a complex balance between reward-seeking and self-limiting behaviour [8].
Due to the limited methodologies allowing us to directly tap into these brain processes while
investigating rewarding behaviour, efforts have been made to identify peripheral biomarkers
that are more easily accessible while still being informative on processes involved in pleasure-
seeking behaviour. Beta-endorphin, an endogenous opioid neuropeptide, is such a peripheral
biomarker and has most often been put forward as the ‘pleasure hormone’ [9]. Opioid receptors
have been found in the abovementioned areas of brain (VTA and NA), suggesting that
endorphins will influence the pleasure and reward system in the brain. In this line, beta-
endorphin is one of the most studied as a peripheral biomarker in the context of pleasurable
activities such as physical exercise, sexual intercourse, eating, etc. [9].
Recent studies suggest, however, that blood-based assessments of beta-endorphin might not
fully reflect brain processes, including changes in the brain reward system, because these large
molecules will not directly pass the blood-brain barrier (BBB) [10]. In light of this, attention
has shifted towards the lipid-based endocannabinoids, specifically 2-arachidonoylglycerol (2-
AG) and anandamide (AEA), which can pass the BBB [11]. Research implicates the role of
endocannabinoids in addiction [12, 13] but also in the reward system, depression and pain
control [14].
Sexuality
While sexual activity isn’t necessarily a part of the BDSM interaction, a play is more often than
not conducted within an erotic context [1]. In this line, a survey of Fetlife participants conducted
by our group in 2017 (n=364) indicated that 87% of the respondents experience BDSM as being
erotic and that 70% combined BDSM with sex at least regularly (unpublished data). This is
corroborated by an interview-based study in which practitioners elaborate upon the sexual
nature of their BDSM experiences [15].
Sexual motivation is closely linked to the pleasure and reward system, and the sexual pleasure
cycle depends on dopaminergic neurons of the reward system and the interacting opioid-
endocannabinoid system [16]. A recent functional magnetic resonance imaging (fMRI) study
showed that sexual cues activate the reward system in the brain in both men and women [17].
Beta-endorphin and dopamine are both linked to male sexual arousal [18]. Equally,
endocannabinoids are also known to influence sexual motivation [19] whereas another study
found the endocannabinoid 2-AG to significantly increase after orgasm [20].
The hypothalamus, and more specifically the paraventricular nucleus, has been implicated in
sexual activity and orgasm [21], most likely through the secretion of oxytocin and vasopressin
[22]. Both of these hormones have been linked to sexuality, though their interaction pathway is
not yet fully understood [23]. Nonetheless, oxytocin has been shown to increase VTA activation
in women as a result of sexual stimuli [24].
Sexual hormones, namely testosterone and oestrogens, are also implicated in sexual arousal by
ensuring cerebral integration between autonomic and somatic sexual systems [16]. Testosterone
plays an important part in the male sexual functioning. It modulates almost all the components
of sexual behaviour, and sexual behaviour will in turn influence testosterone concentrations
[25]. While baseline levels of testosterone are not correlated with the intensity of sexual arousal,
extremely low levels have been clearly linked to decreased sexual interest in both women and
men [26]. There is also growing evidence that testosterone therapy can be effective in increasing
sexual desire in men with sexual dysfunction and low testosterone levels as well as
postmenopausal women with low sexual desire [27, 28]. In women, the level of oestradiol also
seems to be positively correlated with sexual motivation [29].
As such, the dopaminergic driven reward system appears to play a crucial role in sexual pleasure
with several hormones such as oxytocin, vasopressin, oestrogens and testosterone to moderate
the interaction between relational connection, sexual motivation and reward.
Pain and stress
Pain is often an important part of BDSM interactions, as the dominant party will usually inflict
some type of painful stimulation upon the submissive [2]. To fully explore the aspect of pain
within a BDSM interaction, the (subjectively experienced) pain intensity needs be measured.
For example, pain perception can be conceptualised by means of visual analogue scales (VAS)
or verbal descriptor scales (VDS) [30].
An arguably more objective measurement is the pain threshold, as this gives us a quantifiable
measure that can be mapped as it fluctuates. Because of this, it is the preferred instrument in
pain research [31]. The pain threshold can be defined as “the amount of stimulus which will
just barely produce a painful sensation under given conditions” [32] as indicated by the subject.
This stimulus usually involves either pressure, temperature or exposure to erosive chemical
substances, and is often gradually up-titrated [31]. Pain thresholds are known to be influenced
by a variety of factors, including age, gender, personality traits and attachment styles [33-36].
While there is still a degree of subjectivity in measuring pain thresholds, they can give some
insight in factors influencing pain in general.
Pain (and fear of pain) will also elicit a stress reaction in the body, which is mediated by cortisol.
This hormone will react to both positive and negative stress and has been linked to BDSM
interactions on several occasions [37, 38], upon which will be elaborated below. Measuring
cortisol levels can therefore tell us more about the stress response of the body to mental or
physical discomfort.
Power dynamics
Power imbalance is a key element in the BDSM interaction, which usually includes a dominant
and submissive party or variations thereof [1]. This is reminiscent of general societal hierarchy
and status-relevant behaviour, which can be broadly divided into dominance (through induction
of fear) and prestige (through admiration and respect) [39]. Social dominance especially has
been shown to have a strong biological basis, with aggression as a common manifestation [40].
For instance the sexual hormone testosterone has been linked to both aggression [41] and social
dominance [42]. The relationship between testosterone and behaviour is complex, with no real
evidence for a correlation between baseline testosterone levels and trait aggression [41].
However, acute changes in testosterone levels in a competition context may explain differences
in aggressive reactions, both in men and women [43]. Interestingly, this correlation seems to be
mediated by trait dominance as well [44]. Recently, the importance of the stress hormone
cortisol in this dynamic has gained ground with the dual hormone hypothesis, which states that
testosterone mainly influences power dynamics when cortisol levels are low [45]. However, not
all studies have been able to replicate these results and more research will be needed to confirm
this hypothesis [41]. High levels of cortisol have also been correlated with social
submissiveness [42]. In line with this, facial dominance (i.e. the degree of dominance
interpreted from facial expression) in women has been associated with lower cortisol levels
[46].
Vasopressin and oxytocin are likewise not only involved in sexual arousal, but also in
dominance and aggression [47, 48]. In males, vasopressin tends to stimulate aggression and
sexual motivation, while it has a more inhibitory effect in females [48]. Oxytocin is widely
regarded as a prosocial hormone, being implicated in empathy, pair bonding, maternal care,
though depending on context it may also elicit antisocial effects [47].
To summarize, the dynamic between testosterone and cortisol has been shown to play an
important role in social dominance, as has the dynamic between vasopressin and oxytocin.
These hormones are also implicated in sexual motivation and sexual behaviour.
Research objective
This systematic review will summarize all peer-reviewed literature surrounding the biology of
consensual BDSM in order to assess the current state of the art and suggest directions for future
research. Because literature on this topic is limited as of yet, it is important to then place these
results in a broader biological context.
Methodology
A systematic literature search was conducted by the authors using the following inclusion and
exclusion criteria:
1) Inclusion criteria
a. Human studies including BDSM participants
b. Using a definition of BDSM that fits in the safe, sane and consensual paradigm
c. At least one biomarker assessed in the study
2) Exclusion criteria
a. Case reports, opinion articles, comment letters and essays without original data
b. Animal studies
c. Studies with a forensic population or sadomasochism in a coercive setting
These criteria were driven by the generally accepted scientific hierarchy of evidence [49]. No
time-limitation was used in the search. A systematic search was done in August 2021 on three
databases: Pubmed, Web of Science and PsycARTICLES. The search stringwas comprised of
two parts. The first part includes all terminology referencing BDSM, while the second part
includes all relevant biomarkers related to brain activity and hormones involved in pain, stress,
sexuality and pleasure as described in the introduction. This resulted in the following:
1) BDSM, masochi*, sadism, sadomasochi*
2) biolog*, biomarker, serum, plasma, blood, hormones, corticosteroid, glucocorticoid,
cortisol, endorphin, endocannabinoid, AEA, 2-AG, testosterone, oxytocin, estrogen,
vasopressin, pain threshold, brain imaging, functional magnetic resonance imaging,
MRI, magnetoencephalography, MEG, electroencephalography, EEG, event-related
potential, ERP
This search strategy resulted in a total of 10 articles which could be included from Pubmed.
The two additional databases yielded no additional results. A summary of the included articles
can be found in table 1.
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Results
Research on peripheral hormones
Sagarin and colleagues were the first to investigate the impact of BDSM interactions on
peripheral cortisol and testosterone levels [37]. They found that cortisol rose significantly
during the scene (i.e. the BDSM interaction) for the submissive counterparts (n=7) but not for
the dominant participants (n=6). When the submissive subjects were female (n=6), a rise in
testosterone levels was also observed. When the couple had a positive feeling about the scene,
significant reductions in cortisol levels could be seen afterward, together with a reported
increase in relationship closeness. These results were less clear in couples reporting the play to
have been of poor quality. Because of the small sample sizes, however, statistical power
remains in question. Additionally, a control group was not included to compare the levels of
cortisol and testosterone.
A later study by Klement and colleagues [38] found similar increases in cortisol levels before
and during a non-sexual BDSM ritual called ‘Dance of Souls’ which includes temporary
weighted or hooked piercings while dancing to rhythmic drums. The participants (n=67) also
reported a subjective decrease in psychological stress.
Notably, Ambler and colleagues were unable to duplicate the cortisol and testosterone effects
in their study, which included 7 switch couples who were randomly assigned a top or bottom
role [50]. Since this is the only study that did not replicate the cortisol effects, it pays to examine
the differences in study design. Firstly, it must be noted that the study contains a very small
sample size, which brings statistical power into question. Secondly, the study chose to focus on
switches . A person identifying as a switch has a greater level of BDSM role fluidity, which
allows them to switch between roles [51]. This could mean that the biological changes
associated with either a dominant or submissive role are less pronounced, although this
hypothesis hasn’t been tested as of yet.
A more recent large-scale study, conducted in the Flemish BDSM community by our group,
found several relevant changes in hormone levels when comparing the blood results of 35
BDSM couples with those of 27 non-BDSM-interested control individuals [52]. It must be
mentioned that this is not an ideal comparison, since the relationship between the dominant and
submissive party may be a confounding factor that is not accounted for in the non-dyadic
control group. Blood samples were taken at three points in time: firstly right before play,
secondly right after play and thirdly fifteen to thirty minutes after play to account for aftercare
(i.e. the period of time after play for intimate contact and reflection). ELISA analyses assessed
the plasma concentrations of beta-endorphin, endocannabinoids (AEA, 2-AG), cortisol,
testosterone, oestrogen, vasopressin and oxytocin in each of the subjects. Results showed that
both endocannabinoids and cortisol levels significantly increased in submissives during the
BDSM interaction and that these increases were intercorrelated, which suggests that the
submissives indeed experienced the BDSM interaction as rewarding and pleasurable, and that
this experience was related to the stress levels invoked during play. The type of play seemed to
impact hormones related to reward differently in submissives and dominants. Whereas
increases in endocannabinoids were mainly related to impact play (i.e. pain play) in
submissives, significant increases in endocannabinoid levels in dominants were only found in
those focusing on power play in their interaction. Oxytocin was found to be largely unchanged
in the total group. However, when looking into the dominant group, a significant difference
between men and women could be found, with female dominants having higher oxytocin levels
after the play, which was not found in their male peers (unpublished data). This seems to suggest
that BDSM interactions lead to more feelings of attachment and closeness in female dominants.
No significant changes were found in levels of beta-endorphin, testosterone, oestrogen or
vasopressin.
Taken together, there is clear evidence for cortisol changes in submissives linked to a BDSM
interaction, which suggests involvement of the physiological stress system. As our study also
showed, endocannabinoid changes in submissives suggest that the pleasure and reward system
is likewise involved, mainly driven by pain play. In dominants, this biologically measured
pleasure seemed to be dependent on power play rather than pain play. The role of testosterone
and oxytocin is less evident and should ideally be explored in further research to see if the
above-mentioned results can be replicated.
Research on pain thresholds
The study conducted by our group described above [53] also collected pain threshold data
before and after interaction, using both a pressure and temperature stimulus. These findings
suggest that both the dominant and submissive group have an overall higher heat pain threshold
than the control group. These differences in the submissive group seemed to be driven by
minimalizing assumptions and cognitions about pain in general. Additionally, submissives
showed a trend towards a temporary additional increase in their heat pain threshold directly
after a BDSM interaction.
Defrin and colleagues [54] confirmed the presence of higher pressure pain thresholds in
masochistic individuals (n=17) compared to controls (n=17). This study would have also
benefited from the inclusion of other BDSM identities to compare pain thresholds and pain
cognitions. Pollok et al. also found that their masochistic group (n=10) consistently rated
painful sensations as more pleasant than the control group, indicating a different approach to
pain even outside the BDSM context [55].
These are controversial findings, since other literature suggests that a decreased pain sensitivity
is only present in submissives within the context of the BDSM interaction [1, 56]. This pain
threshold literature suggests, however, that submissives respond differently to painful stimuli
regardless of context as well.
Research on functional brain imaging
The biological aspects of BDSM can also be researched by looking at brain functioning.
Functional neuroimaging is a technology that allows us to see which parts of the brain are active
during specific mental functions (e.g. when looking at certain pictures, or when performing a
specific task). fMRI is such an imaging technique.
Kamping and colleagues researched the contextual modulation of pain in masochists (n=16)
compared to a control group (n=16), specifically employing fMRI [56]. They found that painful
stimuli were reported as substantially reduced in experienced intensity when paired with
masochistic images. The fMRI data suggests that this context-dependent pain modulation takes
place in the parietal operculum, a brain region that has been implicated in the detection of tactile
and sensorial input, including painful stimuli [57]. Moreover, tactile stimulation involving the
parietal operculum has also been associated to the activity of the ventral striatum, part of the
brain reward system [58]. An interesting addition to this study would have been to include other
BDSM identities such as dominants, to further investigate the importance of the BDSM context
on pain perception.
Stark and colleagues [59] likewise used the fMRI technique, only they were interested in the
emotional processing differences of different stimuli. An SM-interested group (n=12) and a
non-SM-interested group (n=12) were presented with visual stimuli of a neutral, disgusting,
erotic or sadomasochistic nature, while regions of interest concerning emotional processing
were measured by fMRI. While the non-SM group experienced the sadomasochistic pictures in
a similar way to the disgust-inducing pictures, the SM group reacted similarly to the
sadomasochistic images as they did to the erotic images, with an activation of the ventral
striatum. As mentioned above, this is implicated in the pleasure and reward system [58], which
is in turn implicated in both sexual arousal [16] and by means of peripheral hormones in BDSM
interactions as well [52]. Despite the interesting premise, the researchers don’t focus on the
neurobiology of BDSM but rather use the SM group as a means of differentiating between
erotic and disgust-inducing reactions in the brain. Because of this, the outcome of the study is
not necessarily focused on the biology of BDSM and the implications of their results are not
discussed as such.
Pollok and colleagues [55] conducted research regarding the difference in pain sensitivity
between masochistic individuals (n=10),patients with fibromyalgia (n=10) (a functional
disorder, i.e. a disorder with no detectable structural abnormalities , which is characterized by
generalised pain) and a control group (n=10). This study used magnetoencephalography
(MEG), another type of functional neuroimaging. They found that the process of sensory gating
(i.e. attenuation after repetitive tactile stimuli) is not activated in the masochistic group,
suggesting that these innocuous stimuli are not filtered out as irrelevant. The authors theorized
this decreased sensory gating may be due to a decreased cortical excitability in the primary
somatosensory cortex, perhaps explaining why painful sensations are considered less aversive
by masochists. Important to note is that, like other studies included here, the small sample size
complicates statistical analyses. An interesting addition to this study would have been to include
other BDSM identities such as dominants, to further investigate differences in pain sensitivity
for BDSM-interested individuals.
Luo and Zhang [60] have endeavoured to measure empathy in female submissives (n=32)
compared to controls (n=32) by means of electroencephalography (EEG) and measuring event-
related potentials (ERP). ERP are EEG changes that are time locked to sensory, motor or
cognitive events and can be seen as correlates of mental processes [61]. In their study, Luo et
al. asked participants to look at pictures of women exhibiting signs of fear or pain. They found
differential amplitudes in the fronto-central N1 and P2 and the central/parietal late LPP, which
suggests weakened empathy responses to other people’s suffering and diminished ability to
code the painful expressions as threatening messages in female submissives. This is in line with
comparable research, which showed that physicians also have weakened empathy responses,
presumably due to frequent exposure to people experiencing pain [62]. Remarkably, the survey
part of their study, which gauged empathy traits and empathic ability in general BDSM
practitioners versus controls, also found this decreased empathic ability in submissive women
but not in female dominants or male practitioners, either dominant or submissive. This might
suggest that being in the submissive role influences the empathic ability of women more than
it does men, or that the degree of empathy might steer an interest in submissive behaviour in
women. An interesting addition to this research would have been to include more general
BDSM practitioners in the EEG part of their study as well, to investigate differences in empathy
more profoundly.
Waismann and colleagues [63] equally employ EEG and ERP, differentiating between
responses to visual erotic stimuli in men with a paraphilic interest (n=28) and men without
(n=34). They defined paraphilic interest specifically as having a fetishistic or sadomasochistic
and recruited from community sources, not through medical channels. It is important to note
that they do not differentiate in BDSM identity or experience within the sadomasochistic group.
Both groups were shown slides of either an erotic, a sadomasochistic or a neutral nature. They
found a significant ERP difference in P600, where the paraphilic group had a higher P600
amplitude in response to the paraphilic and the neutral slides, especially in the left frontal cortex.
The non-paraphilic group had a higher P600 amplitude in response to the erotic slides,
specifically in the right parietal area. At other areas, both groups had a high P600 amplitude to
erotic slides. Since P600 is a late component of the ERP, the authors suggest that it is not merely
a sensory response, but a response of recognizing familiar stimuli. The strong response in the
left frontal cortex for the paraphilic group is explained by the authors because of the important
social implications of paraphilic activities, while the right parietal area is mostly involved in
visual association and pattern recognition. The authors go on to discuss the clinical implications
of measuring erotic preference, though it remains unclear why this would need to be objectified
in a clinical context.
Taken together, research into brain region activity patterns related to BDSM interest is
fragmented and very limited, but suggests a role for the parietal operculum [56] and ventral
striatum [59] in the context of the pleasure and reward system, the primary and secondary
somatosensory cortex [55] in the context of pain perception, empathy-related circuits such as
the anterior insula (AI), anterior midcingulate cortex (ACC) and sensorimotor cortex [60] and
the left frontal cortex [63] in the context of social and sexual interactions.
Discussion
Despite the limited research at our disposal, the ten studies included in this review demonstrate
that biological mechanisms underlie both aspects of a BDSM interaction as characteristics
related to BDSM interest. However, it should be noted that the biological processes associated
with BDSM interactions are not necessarily the same as those involved in the development of
BDSM interest.
The neurobiological differences suggest several traits specific to BDSM-interested individuals,
such as differences in pain perception, empathy circuits, pleasure and reward system and social
and sexual systems. However, in the scope of this discussion we will focus on the state changes
related to the BDSM interaction itself.
The hormonal differences found in several studies suggest subjective BDSM interplay to be
related to experiencing stress, pleasure and relational bonding, which may explain the
reinforcing nature of these interactions in BDSM practitioners. These biological processes may
also reflect a biopsychological predisposition for these interests, as corroborated by the fact that
BDSM interest frequently manifests at an early age, often before fifteen years of age, as seen
in a study by our group [2]. In this line, Ten Brink et al. have found that intensity of BDSM
interest was predicted by a secure attachment style amongst others [64].
In the following section, we will endeavour to integrate the state-dependent research done in a
BDSM context with research on the broader biological interaction between pleasure, pain,
power dynamics and sexuality.
Pleasure and pain
Biological processes involved in experiencing pleasure and pain seem to be strongly
interweaved. The endocannabinoid system is known to influence not only the experience of
pleasure and reward but also that of painful sensations [65]. As such, stressful activities have
often been associated with pleasurable effects. A few examples of this are extreme sports, roller
coaster riding, watching horror films, long-distance running and body modification. These
leisure activities could be likened to BDSM, in the sense that the generally unpleasant aspect
of pain or stress is interpreted as pleasurable and desirable in those specific contexts.
Interestingly, research by our group has shown that BDSM practitioners report higher levels of
sensation seeking (thrill seeking, experience seeking and distraction seeking) [66], which is also
seen in individuals seeking out earlier mentioned activities such as extreme sports [67]. The
same links have been found in liking spicy flavours, where it is hypothesized that some people
eat increasingly spicy food in the context of thrill-seeking behaviour, because of the endorphin
release [68]. Spicy food has also been known to increase pain thresholds [69].
The runner’s high, for instance, is a subjective euphoric state induced by long-distance running
and is an example of a physically stressful situation with a pleasurable effect. Cortisol increases
are seen after high-intensity exercise, suggesting a stress-response from the body [70].
Similarly, increases in both endorphins and endocannabinoids have also been found in long-
distance running, suggesting a pleasurable feeling that is subjectively reported by runners as
well [11, 71]. These hormonal changes are very similar to those found in our group of BDSM
practitioners, which also demonstrated an association between the cortisol and endocannabinoid
levels [52].
Not only physical but also psychological stress seems to have these effects as watching horror
films has been associated with both stress and pleasure [72]. A study researching the effect of
violent films on a cohort of young women found increases in cortisol and beta-endorphins,
suggesting the involvement of both the stress and pleasure system [73]. So, as with high-
intensity sports or watching horror films, the experience of BDSM interactions as a physical
and/or psychological stressful event equally seems to lead to increases in endocannabinoids,
consequentially resulting in feelings of reward and a euphoric state after the interaction, which
may well be associated to the mental state referred to as ‘sub-space’ or ‘dom-space’.
Body modification, i.e. tattooing, piercing or scarification, is another example of an activity
clearly associated with pain, and yet actively sought out by some people. A study by
Yamamotovo and colleagues suggests that thermal pain thresholds are strongly influenced by
the context in which the modification is done [74]. Remarkably, Kamping and colleagues came
to the same conclusion when looking at pain perception in masochistic individuals [56]. To
what extent this difference in pain perception is caused by the BDSM context remains to be
seen, since other studies have found this difference regardless of context as mentioned above
[53-55].
Sexuality and pain
Sexual arousal is known to influence pain, with orgasm decreasing pain sensitivity [75] and
sexual activity increasing the pain threshold [21]. Interestingly, oxytocin, typically increased
during intimacy and orgasm, is also known to be secreted in stressful situations and is
sometimes considered as “stress-coping molecule” [23]. Close contact sports could also have
an effect on social bonding, as seen in a study by Rassovsky et al. where oxytocin increased as
a result of certain types of martial arts [76]. Though Sagarin and colleagues didn’t measure
oxytocin specifically, they did find a link between decreases in cortisol and increases in
relationship closeness as a result of a positive play, which implicates this prosocial hormone
[37]. Our study has not found a significant oxytocin change in submissive participants, so the
significance of this hormone remains unclear. It would be an interesting avenue in further
BDSM research to study the link between a BDSM interaction, relationship closeness and
oxytocin.
Pleasure and power
Social dominance has been known to stimulate the reward system [77] and similarly, social
defeat can induce anhedonia, which also suggests an interaction between power play,
dominance and the reward system [78]. These effects may be culturally influenced, however,
as shown in a study by Freeman et al. [79], where a dominance-reinforcing culture shows links
between dominant behaviour and activation of the reward system, and a subordinate-reinforcing
culture shows links between subordinate behaviour and activation of the reward system. Our
study confirmed this link between endocannabinoid increase and power play in dominants [52],
suggesting a state change as a result of dominant behaviour. Further research could also look at
any differences regardless of context, such as trait dominance.
Sexuality and power
As seen in the introduction, several hormones implicated in sexuality also play an important
role in social power structures [25, 26, 41, 42]. . Sexual arousal as a result of dominance or
submission has even been suggested as a mating strategy, resulting in increased reproductive
success [80]. It is hypothesised that this increased success is a result of on the one hand a need
for a partner with a high status (e.g. dominant) and on the other hand a low-ranking partner that
is less prone to infidelity [81].
The fact that hormones such as testosterone, oxytocin and vasopressin are involved in both
sexual behaviour and social hierarchy, strengthens this hypothesis. For instance, one study has
found that oxytocin plays an important role in empathic responses to a sadistic context [82]. In
our study, an increase in oxytocin was found specifically in female dominants (unpublished
data), suggesting a difference in intimacy or attachment between female and male dominants
when it comes to BDSM interactions. Sex differences in oxytocin are known [83], though not
understood enough to explain these differences. The oxytonergic system would be an
interesting avenue of future BDSM research, given its implications in these different biological
processes.
Comparisons to coercive sadism:
When discussing BDSM as a safe, sane and consensual practice, it is important to differentiate
it from pathological behaviour such as coercive sadism, as mentioned in the introduction.
Victims of coercive sadistic practices have not given consent and do not have control, in
contrast to submissives in a consensual BDSM interaction [4]. Likewise, dominants in a
consensual BDSM relationship are a very separate group from coercive sadists. Recent
literature applying cluster analyses on a range of sexual fantasies and behaviours confirms this
difference between BDSM interest and coercive sexual behaviour [84].
As with research on the biology of BDSM, biological processes behind coercive sadism have
not been fully explored, and most literature will look more broadly at the biology of sexual
offending in general, or paraphilic disorders in general. We will discuss these results briefly
and compare them to what is known about BDSM.
A very recent study on peripheral hormones in coercive sadists has shown that testosterone
levels increased when looking at videos of people in emotional distress [85]. This effect was
positively correlated to the subjects’ scores on the Severe Sexual Sadism Scale. The two BDSM
studies that measured testosterone levels in dominants did not find a similar increase [37, 52].
A neuroimaging study compared sadistic sexual offenders with non-sadistic sexual offenders
and a control group [86]. They found increased activity in the left amygdala for the sadistic
group as a response to images depicting inflicted pain, as well as a greater connectivity between
the left amygdala and the right anterior insula. The sadistic group also consistently rated pain
severity higher than the non-sadistic groups, which was positively correlated with anterior
insula activity. The authors argue that involvement of the amygdala links the pain-pictures to
sexual arousal in sadists, and that the anterior insula signifies that rather than callousness
towards pain, sadists draw from a subjective emotional experience when they evaluate pain
severity. To our knowledge, no comparative studies exist that measure the brain activity
patterns of BDSM participants when looking at non-sadomasochistic, pain-depicting images.
However, Erickson and Sagarin did demonstrate that BDSM sadists demonstrate prosocial
sadism (e.g. where consent is explicit) and not everyday sadism [87].
More generally, research on sexual offending finds abnormalities in frontal, temporal and
limbic regions [88-90]. This suggests the presence of more bottom-up driven behaviour in
coercive sadists, associated with cognitive impairment, reductions in impulse controland
emotional regulation problems that are thus far not seen in BDSM participants [1].
Additional research on dominant behaviour within the BDSM context may help with illustrating
further differences between consensual sexual dominance or sadism on one hand and coercive
sadism on the other.
Limitations
There are several limitations to this review that need to be addressed.
Firstly, the lack of consensus regarding the definition of BDSM poses some challenges. This
results for instance in a difference of terminology used in the included studies. Some studies
will reference the submissive party as “bottoms”, others as “masochists” or “submissives”. The
same is true for the dominant party. Another difficulty in this heterogeneous terminology is the
sexual component. While BDSM is often linked with sexual activity, not all BDSM
practitioners agree with this [91]. The role of sexuality remains a topic of discussion in the
scientific community [1].
Another important bias to address is the WEIRD bias. This states that most studies still focus
on western, educated, industrialized, rich, and democratic societies [92]. When we review the
ten studies included in this review, we must conclude that this is the case for all but two (see
table 1). This has of course potential implications for the generalizability of the study results.
International studies are needed to assess what cultural and societal differences may arise.
What must also be mentioned is the distinct lack of studies in this particular field, which means
that most of the results have not as of yet been replicated in other research. This means that it
is difficult to draw conclusions on both trait and state findings, and that causal implications
cannot be made. Small sample sizes also diminish the statistical power of the results.
Clinical implications
As our understanding of the biology of BDSM grows, so does the opportunity to help in the
destigmatization of BDSM in general. Historically, it has been pathologized by its inclusion in
for instance the Diagnostic and Statistical Manuel of Mental Disorders (DSM) and the
International Classification of Diseases (ICD). Though there has been some progress, it is still
included in the 5th edition (DSM-5) today as “sexual sadism”, “sexual masochism” and
“fetishism” [93]. On a more promising note, those diagnoses have been eliminated from the
most recent 11th edition of the ICD, replaced instead by “coercive sexual sadism disorder” [94].
By normalizing the biological processes that underlie BDSM activities, we hope to strengthen
the argument that it does not belong in the psychiatric or forensic field and needs to be firmly
distinguished from paraphilias as described in the DSM or ICD.
Conclusion
BDSM refers to a broad set of behavioural, relational and sexual interactions and is influenced
by several psychological, social and biological processes. Because it is not easily defined and
encompasses many aspects of pain, pleasure, sexuality and power structures, the biological
mechanisms associated with BDSM will be equally broad.
As for the important aspect of pain within the BDSM interaction, Dunkley and colleagues have
made an integrative model of how pain may be processed as pleasurable in the context of BDSM
[95]. This model draws on the existing psychological processes known to be involved in BDSM,
such as the altered states of consciousness (e.g. “sub-space”), sexual arousal, social bonding,
the importance of control and volition, etc. They use these to theorize on the process of
experiencing pain as a welcome sensation. The model also encompasses several biological
factors which are discussed in this review as well. They implicate the importance of the pleasure
and reward system to modulate painful sensations through dopamine and endocannabinoids, as
well as sexual arousal through oxytocin. Lastly, they also link cortisol increases to the
involvement of the stress system.
We have endeavoured to summarize the known biological processes in a model, by drawing on
these different aspects, as well power structures (see figure 2). The pain and power dynamics
which are so often present in a BDSM interaction will translate biologically in the activation of
several hormones such as cortisol, testosterone and vasopressin. Of these hormones, cortisol
has been most strongly implicated in BDSM interactions, with several studies finding evidence
for a physical stress reaction in the body during a BDSM play. Testosterone is likewise
implicated in female submissives [37], though this has yet to be replicated. Meanwhile,
experience of pleasure and sexuality, regulated by different hormones such as
endocannabinoids, beta-endorphin, oxytocin and sex hormones, will colour and direct the
BDSM experience and influence the experience of pain and power dynamics as well. Of these,
the endocannabinoids have been found to change because of a BDSM interaction [52],
suggesting a clear involvement of the pleasure and reward system. Oxytocin was implicated in
female dominants in the same study, though this has not been investigated further by other
research. Future scientific research will help to shed further light on these biological processes
and hopefully contribute to reducing the stigma that BDSM practitioners still endure in our
society.
-- INSERT FIGURE 2 ABOUT HERE --
Table 1: included studies on biology of BDSM
Study
Population
Methodology
Results
Waismann et
al. (2003)
UK
Paraphilic
(fetishistic and
sadomasochistic)
men (n=28; mean
age 36)
versus non-
paraphilic
heterosexual men
(n=34; mean age
29)
ERP measured by means
of EEG as population was
presented with visual
stimuli of erotic,
sadomasochistic or neutral
slides
In the paraphilic group
strong P600 responses in
the left frontal cortex to
the paraphilic stimuli. In
the control group strong
P600 responses in the
right parietal area to the
erotic slides.
Stark et al.
(2005)
Germany
Group with
sadomasochistic
interest (n=12; 6
female; mean age
28) versus group
without
sadomasochistic
interest (n=12; 6
female; mean age
28)
fMRI to measure regions
of interest concerned with
emotional processing as
population was presented
with visual stimuli of a
neutral, disgust-inducing,
erotic or sadomasochistic
nature
The sadomasochistic
group had equal positive
reactions to the erotic and
the sadomasochistic
pictures, which activated
mainly the ventral
striatum, implicated in the
pleasure and reward
system
Sagarin et al.
(2009)
USA
Sadomasochistic
practitioners
(n=13; 6 female;
mean age 45)
Salivary samples were
taken before and after a
BDSM interaction to
measure cortisol and
testosterone levels; two
relationship closeness
measures were taken
Increase of cortisol in
bottoms; increase in
testosterone in female
bottoms; decrease of
cortisol and increase of
relationship closeness
later on if positive feeling
about the scene
Pollok et al.
(2010)
Masochistic
individuals (n=10:
MEG data were measured
while administering a
No sensory gating in
masochists after repetitive
Germany
5 female; mean
age 39) versus
fibromyalgia
patients (n=10; 9
female; mean age
54) versus
controls matched
in age and gender
conditioning stimulus
followed by a tactile test
stimulus; MRI images
were taken to corroborate
MEG data; pain thresholds
were measured before and
after stimulus
tactile stimuli; higher pain
thresholds for masochists
versus controls;
involvement of
somatosensory cortex in
pain thresholds
Defrin et al.
(2015)
Israel
Masochistic
individuals (n=17;
7 female; mean
age 28) versus
control group
(n=17; 8 female;
mean age 28)
Pain thresholds, pain
cognitions
Higher pressure pain
thresholds in masochists
Kamping et
al. (2016)
Germany
Masochistic
individuals (n=16;
8 female; mean
age 42) versus
control group
(n=16; 12 female;
mean age 40)
fMRI to measure regions
of interest concerning pain
perception and modulation
as population was
presented with visual
stimuli of a masochistic,
neutral, positive or
negative nature while also
pairing a painful laser
stimulus; pain perception
measured by visual
analogue scale
Reduced pain perception
of masochists in BDSM
context; involvement of
parietal operculum in pain
modulation
Klement et
al. (2017)
USA
Extreme ritual
“Dance of Souls”
participants
(n=67; 33 female;
mean age 49)
Salivary samples were
taken before and after the
“Dance of Souls” to
measure cortisol levels
Increase of cortisol in
participants undergoing
the ritual
Luo et al.
(2018)
China
Masochistic
women (n=32;
mean age 21)
versus non-
masochistic
women (n=32;
mean age 21)
ERP measured by means
of EEG as population was
presented with images of
female faces with either a
neutral or painful
expression in either a
general or BDSM-related
context
Weakened empathic
responses to fear or pain
by masochists;
involvement of AI, ACC
and sensorimotor cortex
Wuyts et al.
(2020)
Belgium
Dominant BDSM
practitioners
(n=34; 9 female;
mean age 44)
versus submissive
BDSM
practitioners
(n=33; 24 female;
mean age 38)
versus controls
(n=24; 11 female;
mean age 34)
Blood samples were taken
before, right after, and
15min after a BDSM
interaction to measure
levels of cortisol, beta-
endorphin,
endocannabinoids,
testosterone, oestrogen,
oxytocin by means of
ELISA
Associated increase of
both cortisol and
endocannabinoids;
increase of oxytocin in
female dominants
compared to male
counterparts
Wuyts et al.
(2021)
Belgium
Dominant BDSM
practitioners
(n=34; 9 female;
mean age 44)
versus submissive
BDSM
practitioners
(n=33; 24 female;
mean age 38)
versus controls
(n=24; 11 female;
mean age 34)
Pain thresholds were
measured by means of a
pressure and temperature
stimulus before, right
after, and 15min after a
BDSM interaction; pain
cognitions were measured
by means of the PCS and
FPQ
Higher heat pain
thresholds in BDSM
participants; increase of
heat pain threshold in
submissives
ERP = event related potentials ; EEG = electroencephalography ; fMRI = functional magnetic
resonance imaging ; MEG = magnetoencephalography ; MRI = magnetic resonance imaging ;
AI = anterior insula ; ACC = anterior midcingulate cortex ; ELISA = enzyme linked
immunosorbent assays ; PCS = pain catastrophizing scale ; FPQ = fear of pain questionnaire
Figure 1: Preferred reporting items for systematic review and meta-analysis protocols
(PRISMA) flowchart
Figure 2: biology of BDSM
DA = dopamine; 2-AG = 2-arachidonoylglycerol; AEA = anandamide; HPA-axis =
hypothalamic-pituitary-adrenal axis
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