Romantic partner embraces reduce cortisol release after acute

stress induction in women but not in men

Gesa Berretz a, Chantal Cebula a, Blanca Maria Wortelmann a, Panagiota Papadopoulou a,

Oliver T. Wolf b, Sebastian Ocklenburg a, Julian Packheiser a*

a: Institute of Cognitive Neuroscience, Biopsychology, Faculty of Psychology, Ruhr

University Bochum, Germany

b: Institute of Cognitive Neuroscience, Cognitive Psychology, Faculty of Psychology, Ruhr

University Bochum, Germany

* Corresponding Author: Julian Packheiser

Address correspondence to: Julian Packheiser, Abteilung Biopsychologie, Institut für

Kognitive Neurowissenschaft, Fakultät für Psychologie, Ruhr-Universität Bochum,

Universitätsstraße 150, D-44780 Bochum, Germany. E-mail: [email protected]

ORCID ID Gesa Berretz: 0000-0002-3513-1946

ORCID ID Oliver T. Wolf: 0000-0002-9320-2124

ORCID ID Sebastian Ocklenburg: 0000-0001-5882-3200

ORCID ID Julian Packheiser: 0000-0001-9805-6755

1 Abstract

Stress is omnipresent in our everyday lives. It is therefore critical to identify potential stress- buffering behaviors that can help to prevent the negative effects of acute stress in daily life.

Massages, a form of social touch, are an effective buffer against both the endocrinological and sympathetic stress response in women. However, for other forms of social touch, potential stress-buffering effects have not been investigated in detail. Furthermore, the possible stress- buffering effects of social touch on men have not been investigated so far. The present study focused on embracing, one of the most common forms of social touch across many cultures.

We used a short-term embrace between romantic partners as a social touch intervention prior to the induction of acute stress via the Socially Evaluated Cold Pressor Test. Women who embraced their partner prior to being stressed showed a reduced cortisol response compared to a control group in which no embrace occurred. No stress-buffering effect could be observed in men. No differences between the embrace and control group were observed regarding sympathetic nervous system activation measured via blood pressure. These findings suggest that in females, short-term embraces prior to stressful social situations such as examinations or stress interviews can reduce the cortisol response in that situation

Keywords: social touch; oxytocin; hug; affective touch; stress buffer

2 Introduction

Embracing is one of the most prevalent forms of social touch in everyday life and across cultures (Forsell & Åström, 2012). They are used to greet others, convey and but can also be used in negative situations to console people who feel sad or depressed

(Ocklenburg et al., 2018). Embraces have been demonstrated to be influenced by the affective state of the embracing individuals (Packheiser et al., 2019; Packheiser, Schmitz, et al., 2020).

Furthermore, embracing your partner elicits stronger positive emotional responses both on the behavioral and neurophysiological level compared to embracing objects (Packheiser, Berretz, et al., 2020). The positive emotional effects of embracing might explain why it is linked to benefits on physical and mental health. For example, embracing has been shown to reduce blood pressure (Light, Grewen, & Amico, 2005), is associated with decreases in inflammation

(van Raalte & Floyd, 2020) and with increased subjective well-being (Ocklenburg et al.,

2021) and is linked to a reduced risk of infection and an accelerated recovery from viral diseases (Cohen, Janicki-Deverts, Turner, & Doyle, 2015). The latter study suggested that this health benefit might be due to the potential buffering effects of embraces on the stress response as this effect was especially dominant on days with interpersonal tension.

Stress is one of the leading factors associated with a variety of mental disorders such as , burn-out or disorders (Berretz, Wolf, Güntürkün, & Ocklenburg, 2020;

Iacovides, Fountoulakis, Kaprinis, & Kaprinis, 2003; Shin & Liberzon, 2010). While these disorders are generally linked to long-term stress exposure, acute stress has been, amongst other things, associated with increases in negative mood indicating the importance of regulating stress for subjective well-being as well (Bolger, DeLongis, Kessler, & Schilling,

1989). On the physiological level, the stress response comprises two separate but interconnected branches. The activation of the sympathetic nervous system leads to a fast release of adrenalin from the adrenal medulla as well as noradrenaline from postganglionic 3 neurons resulting in an increase of heart rate, blood pressure and breathing frequency (Ulrich-

Lai & Herman, 2009). This release is paralleled by the nucleus coeruleus leading to an increase of adrenalin and noradrenalin in the brain which is connected to the subjective of stress (Joëls & Baram, 2009). The other branch consists of the hypothalamic- pituitary-adrenocortical (HPA) axis. Here, secretion of corticotropine-releasing-hormone and arginine-vasopressin from the hypothalamic paraventricular nucleus cause the release of adrenocorticotropic hormone from the pituitary into the circulatory system. This leads to release of glucocorticoid hormones from the adrenal cortex. In humans, cortisol represents the main glucocorticoid and is therefore regarded as one of the major stress hormones (de Kloet,

Joëls, & Holsboer, 2005).

Major stressors that have been demonstrated to activate these two systems are pressure to perform, uncontrollability and social evaluation (Birkett, 2011; Mitchell, Greenbaum, Vogel,

Mawritz, & Keating, 2019). While confrontation with other people can elicit a stress reaction, the presence and the support of others, especially through social touch, can also act as a buffer towards the bodily stress response. For example, Heinrichs, Baumgartner, Kirschbaum, and

Ehlert (2003) exposed men to the Trier Social Stress Test (TSST), a stress induction paradigm exerting psychosocial stress (Kirschbaum, Pirke, & Hellhammer, 1993), and found that a preparation for the social evaluation of TSST with social support reduced the expression of cortisol. Furthermore, they also administered oxytocin which has been demonstrated to exert stress-attenuating effects (Smith & Wang, 2014) and is released especially through social touch (Tang et al., 2020). Heinrichs et al. (2003) found that social support plus oxytocin provided an even stronger buffering effect for the secretion of cortisol compared to social support by itself.

Prolonged social touch and the associated increased levels of oxytocin have been suggested to induce a shift from sympathetic to parasympathetic activation in animal studies (Uvnäs-

4 Moberg, 1998) and have been demonstrated to increase psychophysiological in women (Meier et al., 2020). Furthermore, embracing a human-shaped cushion during a phone conversation has been shown to reduce cortisol levels in women compared to a phone call without the embrace (Sumioka, Nakae, Kanai, & Ishiguro, 2013). However, these studies did not perform a stress intervention calling into question whether these effects apply to acute stress reactions of the body. To our knowledge, only a single study investigated the role of prolonged physical contact on the acute stress response. Ditzen et al. (2007) studied the effects of different types of couple interactions on cortisol and heart rate responses elicited via the TSST in women. In three experimental groups, they tested the effects of no interactions between romantic partners, verbal social support and physical social support in form of a 10- minute long shoulder massage on the sympathetic nervous system and the HPA axis. They found significant decreases of both heart rate and cortisol release exclusively in the physical support group suggesting that physical contact provides the most effective buffer against the bodily stress response.

In the present study, we investigated the role of physical contact by a more everyday applicable means, i.e. via a short embrace between partners as embraces have been indicated to be a viable stress buffer in stressful situations (Cohen et al., 2015). To this end, we invited romantic couples and randomly divided them into two groups. One group was asked to perform a mutual embrace before undergoing a joint stress induction procedure. The other group did not embrace each other, and the partners only provided social support during the joint testing procedure. Since previous studies only investigated the effects of physical contact on the stress response in women, we explicitly also investigated these effects in men. We hypothesized that the embracing group demonstrates a reduced cortisol and blood pressure response to the stressor in accordance with previous findings.

5 Methods

Participants

A total of 76 participants with an average age of 22.30 years (standard deviation: 2.24; range:

19 to 32 years) were included in the final sample. 36 participants were male and 40 were female. Participants were invited as romantic couples and therefore always came in pairs. A post -hoc power analysis was conducted using g*Power 3.1.9.7 (Faul, Erdfelder, Lang, &

Buchner, 2007). The sample size was sufficient to achieve 86% power to find a group difference between the two experimental groups in a mixed model based on the effects observed by Ditzen et al. (2007). They found a medium-sized effect between the physical contact group and the social support group as well as the group without any interactions (d =

0.57). All participants included in the final sample had no history of mental or neurodevelopmental disorders, were non-smokers and had no prior experience with the experimental paradigm. Furthermore, the body mass index was between 18.5 and 27. The study was approved by the local ethics committee at the faculty of psychology at Ruhr

University Bochum. All participants gave written informed consent and were treated in accordance with the declaration of Helsinki.

Experimental procedure All experiments were conducted between 1pm to 6pm to control for effects of the circadian rhythm on cortisol. To prevent the contamination of saliva samples, the participants were explicitly asked not to eat or drink anything apart from drinking water for one hour before the procedure. Couples arrived jointly and were then divided randomly into one of two experimental groups. In the control condition, couples underwent a stress induction procedure

6 (see below for detail) together. In the embrace condition, participants went through the identical procedure but also embraced each other once during the experiment.

After being picked up by the experimenter and being seated in the experimental room, participants in both groups first provided informed written consent. After filling out demographic questionnaires, a baseline saliva sample as well as systolic and diastolic blood pressure were taken. Furthermore, participants filled out the Positive and Negative

Scale (PANAS, (Watson, Clark, & Tellegen, 1988). Following baseline measurement, the experimenter either left the room immediately to allow for the stress induction to commence

(control condition) or instructed the participants to embrace once they left the room and until they re-entered the room (embrace condition). The experimenter then left and waited for exactly 20s after which they re-entered the room to signal the end of the embrace. As in the control group, the experimenter then left and the stress induction procedure began.

In both groups, a previously unknown experimenter (randomly chosen to be female or male) entered the room dressed in a lab coat. This experimenter was briefed to act neutral and distanced to the participants both during the instructions and during the stress procedure itself.

The participants were then informed about the stress procedure, namely the Socially

Evaluated Cold Pressor Test (SECPT) which has been evaluated for group testing scenarios

(Minkley, Schröder, Wolf, & Kirchner, 2014). The SECPT requires participants to place their hand with spread fingers in an ice-cold water bath (0 - 4ºC) for a maximum of three minutes upon which the experimenter ended the procedure. Participants were instructed that they could remove their hand if the procedure could no longer be endured at any time. During the

SECPT, participants were furthermore filmed by a camera to which they were asked to constantly hold eye contact. They were also asked not to talk during the procedure. Any violations of these instructions were continuously remarked by the experimenter. After one minute of the SECPT start, the blood pressure was taken again, regardless of whether the

7 procedure was aborted or not. After the procedure had ended, another saliva sample was immediately taken and the participants filled out another PANAS questionnaire as well as subjective stress questionnaires about the SECPT. Here, the participants had to indicate on a scale from 0 – 100 how difficult, painful, stressful and unpleasant the SECPT procedure had been. The experimenter for the SECPT then left the room and the original experimenter came back.

Following the SECPT, the couples were separated from each other to fill out the Relationship

Assessment Scale (RAS) in an unbiased manner (Hendrick, Dicke, & Hendrick, 1998). The

RAS is a 7-item questionnaire that assesses the relationship quality on a 5-point Likert scale.

Furthermore, both 15 minutes and 25 minutes after the conclusion of the SECPT, another saliva sample, blood pressure and affective ratings using the PANAS questionnaire were taken from the participants.

Figure 1. A) In the embrace condition, participants filled out questionnaires and provided a baseline measurement for cortisol, blood pressure and affective state prior to the experimental onset. After this was concluded, a 20s embrace in the absence of the experimenter took place. Following the embrace, the couples were subjected to the SECPT in a group setting with another measurement cycle. 15 and 25 minutes after the SECPT was concluded, another measurement was conducted. B) Same as in A), but the partners did not embrace prior to the SECPT.

Cortisol measurements 8 Saliva was collected polypropylene micro salivettes (Sarstedt, Nürmbrecht, Germany). After the end of the experimental session, the samples were stored at -20 ºC until further analysis.

Cortisol was assessed in an in-house laboratory of the Genetic Psychology department at Ruhr

University Bochum by using a cortisol enzyme-linked immunosorbent assay (Cortisol Saliva

ELISA, IBL, Hamburg, Germany). The intra‐ assay coefficients of variance (CV) were below

5% and interassay CVs were below 15%.

Cardiovascular measurements Blood pressure was taken on the left arm using an M700 Intelli IT blood pressure monitor

(OMRON, Kyoto, Japan). The left arm was used as the participants were instructed to submerge their right hand under water. The cuff was situated approximately 2 cm above the elbow bend. Participants were asked to rest their arm on the table and remain silent during the measurement to ensure valid results.

Statistical analyses Statistical evaluation was performed using R version 4.1.0. Relationship satisfaction was compared between both groups using independent samples t-tests. Cortisol data was log- transformed prior to further analysis. Data that was obtained at multiple measurement time points (cortisol, blood pressure, affective state) was baseline-corrected by subtracting the baseline measurements from the measurement during the SECPT as well as 15 and 25 minutes post SECPT. We then ran a linear mixed model analysis using the lme4 and lmerTest package (Bates, Mächler, Bolker, & Walker, 2014; Kuznetsova, Brockhoff, & Christensen,

2017) as these models can include subjects as a random factor in addition to fixed effects allowing for better generalization to the underlying population (Barr, Levy, Scheepers, &

Tily, 2013). The model was run with cortisol, systolic blood pressure, diastolic blood pressure as well as positive and negative affective state as dependent variables and measurement time point (levels: SECPT, 15min post SECPT, 25min post SECPT), condition (levels: control,

9 embracing) and sex (levels: male, female) as independent variables. For cortisol, we also included the use of oral contraceptives (OCs) as a covariate (levels: female OCs, female no

OCs, males no OCs) due to its known effect of cortisol. Post-hoc tests were performed using the emmeans function to correct for multiple comparisons (Bonferroni method) and estimate the effect size of significant differences. Data that was only obtained during the SECPT, i.e. difficulty, painfulness, stressfulness and unpleasantness of the SECPT as well as the duration of the hand in the water were evaluated using a linear model with each of these parameters as dependent variable and group and sex as independent variables.

10 Results Relationship satisfaction Relationship satisfaction in the overall sample was high with a mean RAS score of 30.88 (SD

= ± 3.99, maximum score = 35). The two experimental groups showed no difference in relationship satisfaction (t(73) = 0.54, p = .593). There was furthermore no difference in relationship satisfaction between females and males (t(73) = 0.16, p = .872).

Cortisol For changes in cortisol over time, we observed a three-way interaction between condition, sex and the measurement time point at 25 min post SECPT (β = 0.56 [0.03 – 1.08], SE = 0.27, t =

2.04, p = .043). Bonferroni corrected post hoc tests revealed significantly less cortisol in the embracing compared to the control condition at the 25 min post SECPT measurement for females only (t = 2.26, p = .026, d = 1.09 [0.13 – 2.05], see figure 2). Furthermore, there was a significant difference between males and females in the embracing condition at the 25 min post SECPT measurement (t = 3.10, p = .006, d = 3.37 [1.18 – 5.56]).

11 Figure 2. Changes in cortisol concentration relative to baseline for females (left) and males (right) during the SECPT and 15 minutes as well as 25 minutes post SECPT for the embrace and control condition. Error bars represent the 95% interval. Group differences between the conditions are marked. ** = p < .01.

While the effect was unlikely moderated by the use of OCs as the covariate did not reach significance in the model (β = -0.25 [-0.58 – 0.09], SE = 0.18, t = 1.37, p = .174), we nonetheless conducted an exploratory analysis to identify whether the use of OCs could have had an effect on the efficacy of the embrace in buffering the cortisol response. This was done as there was a slight but non-significant imbalance between the use of OCs in both groups.

Overall, 26 women took OCs in our study compared to 14 freely cycling women. 11 or 58% of women in the control condition took OCs and 15 or 71% of women in the embracing condition (χ² = 0.80, p = .370). Instead of sex, we used the use of OCs (levels: yes, no) as an independent variable in this model. We found a significant three-way interaction between the

25 min post SECPT measurement, condition and the use of OCs (β = -0.97 [-1.69 – 0.25], SE

12 = 0.38, t = 2.53, p = .026). Bonferroni corrected post hoc test revealed that there was a significantly reduced cortisol response in the embracing compared to the control condition at the 25 min post SECPT measurements (t = 3.63, p < .001, d = 2.71 [1.18 – 4.25], see figure

3).

Figure 3. Changes in cortisol concentration relative to baseline for females using OCs (left) and free cycling females (right) during the SECPT and 15 minutes as well as 25 minutes post SECPT for the embrace and control condition. Error bars represent the 95% confidence interval. Group differences between the conditions are marked. *** =p < .001.

Blood pressure For diastolic blood pressure, we found a significant main effect of measurement time point at both the 15 min (β = -14.36 [-17.46 – -11.25], SE = 1.61, t = 9.06, p < .001) and 25 min post

SECPT measurement (β = -14.92 [-18.03– -11.82], SE = 1.59, t = 9.42, p < .001). Bonferroni corrected post hoc test revealed a significant decrease in diastolic blood pressure following

13 the SECPT both at the 15 min (t = 9.06, p < .001, d = 1.47 [1.12 – 1.82]) and 25 min post

SECPT measurement (t = 9.42, p < .001, d = 1.53 [1.18 – 1.88], see figure 4).

Figure 4. Changes in diastolic blood pressure relative to baseline for females (left) and males (right) during the SECPT and 15 minutes as well as 25 minutes post SECPT for the embrace and control condition. Error bars represent the 95% confidence interval.

For systolic blood pressure, we found comparable results as there was also a significant main effect of measurement time point at both the 15 min (β = -18.03 [-21.66 – -14.95], SE = 1.71, t = 10.69, p < .001) and 25 min post SECPT measurement (β = -19.85 [-23.21– -16.50], SE =

1.71, t = 9.42, p < .001). As for diastolic blood pressure, Bonferroni corrected post-hoc test revealed a significant decrease in systolic blood pressure following the SECPT both at the 15 min (t = 10.69, p < .001, d = 1.73 [1.37 – 2.09]) and 25 min post SECPT measurement (t =

9.42, p < .001, d = 1.88 [1.52 – 2.25], see figure 5).

14 Figure 5. Changes in systolic blood pressure relative to baseline for females (left) and males (right) during the SECPT and 15 minutes as well as 25 minutes post SECPT for the embrace and control condition. Error bars represent the 95% confidence interval.

Affective state For positive affective state, there was a significant main effect of measurement time point at the 25 min post SECPT measurement (β = -0.26 [-0.39 – -0.13], SE = 0.07, t = 3.91, p

< .001). Bonferroni-corrected post-hoc tests revealed a significant decrease in positive affect following the SECPT at the 25 min post SECPT measurement (t = 3.91, p < .001, d = 0.63

[0.31 – 0.96], see figure 6).

15 Figure 6. Changes in positive affect relative to baseline for females (left) and males (right) during the SECPT and 15 minutes as well as 25 minutes post SECPT for the embrace and control condition. Error bars represent the 95% confidence interval.

For negative affective state, there was a significant main effect of measurement time point at the 15 min measurement (β = -0.31 [-0.58 – -0.05], SE = 0.13, t = 2.36, p = .020) and 25 min post SECPT measurement (β = -0.37 [-0.63 – -0.11], SE = 0.13, t = 2.78, p = .006). However,

Bonferroni-corrected posthoc tests revealed a significant decrease in negative affect only at the 25 min post SECPT measurement compared to the SECPT itself (t = 2.78, p = .018, d =

0.45 [0.13 – 0.77], see figure 7).

16 Figure 7. Changes in negative affect relative to baseline for females (left) and males (right) during the SECPT and 15 minutes as well as 25 minutes post SECPT for the embrace and control condition. Error bars represent the 95% confidence interval.

Subjective SECPT ratings and SECPT duration We neither found any main effects of condition or sex, nor any interaction for the difficulty, painfulness, stressfulness or unpleasantness ratings of the SECPT. The same was true for the time that the participants spent in the ice-cold water. Descriptive values for these measures can be found in table 1.

Table 1. Descriptive values (mean value and standard error) of the SECPT ratings and the duration of the SECPT broken down by condition and sex.

Difficulty Painfulness Stressfulness Unpleasantness Duration in s Embrace 69.0 ± 6.4 55.1 ± 6.9 44.3 ± 5.7 73.8 ± 5.3 148 ± 11 female Embrace 62.8 ± 6.9 45.6 ± 7.5 41.7 ± 6.2 62.8 ± 5.7 166 ± 12 male Control 70.5 ± 6.7 61.6 ± 7.3 54.7 ± 6.0 74.7 ± 5.5 144 ± 11 female Control 51.1 ± 6.9 54.4 ± 7.5 44.4 ± 6.2 67.8 ± 5.7 170 ± 12 male Discussion 17 In the present study, we investigated the efficacy of a short-term embrace with a 20s duration on the physiological stress response. To this end, we invited romantic couples and subjected them to the SECPT in a joint testing environment. One group was additionally instructed to embrace each other prior to the stress procedure. We hypothesized that both responses from the sympathetic nervous system as well as from the HPA axis would be decreased through the application of social touch. We could partly confirm our hypothesis as there was a significantly reduced cortisol response in the embracing group compared to the control group.

This effect was however selective to female participants and could not be observed in males.

Blood pressure as a marker of sympathetic nervous system activity was not modulated by the embrace.

A noteworthy finding of our study is the pronounced sex difference in the influence of the embrace on cortisol changes due to the SECPT. Previous studies who investigated the role of physical contact and social touch on cortisol release exclusively studied women (Ditzen et al.,

2007; Sumioka et al., 2013) and it was therefore unclear if these results generalize to men as well. We found no evidence that men benefitted from a short-term embrace as a potential stress buffer and our results indicated that this effect is specific to women. This effect was not mediated by differences in relationship quality as there were no difference in relationship satisfaction between females and males. A conceivable explanation for this sex difference could relate to varying levels of oxytocin release between males and females following the embrace. Oxytocin is hypothesized to inhibit the synthesis of adrenocorticotropic hormone in the pituitary gland as it resembles vasopressin in its molecular structure (Gimpl & Fahrenholz,

2001). Rising oxytocin levels are associated with decreases in vasopressin ultimately resulting in decreased cortisol secretion in the human body (Gimpl & Fahrenholz, 2001). While we did not measure oxytocin in the present study, a meta-analytic study on sex differences in affective touch has demonstrated that women perceive affective touch as significantly more

18 pleasant compared to men (Russo, Ottaviani, & Spitoni, 2020). Moreover, oxytocin has been demonstrated to be directly correlated with the perceived pleasantness of gentle touch

(Portnova, Proskurnina, Sokolova, Skorokhodov, & Varlamov, 2020). Therefore, the mutual embrace might have elicited higher levels of perceived pleasantness and thus higher levels of oxytocin release in women compared to men which could explain the observed difference.

Interestingly, an exploratory analysis between women using OCs and free-cycling women demonstrated that the cortisol buffering effect was only present in the latter group. While a blunted cortisol response is in accordance with the literature for the OC group (Kirschbaum,

Pirke, & Hellhammer, 1995), we did not expect a complete absence of an endocrinological response in this group as OC women also generally demonstrate an increase in cortisol levels in response to acute stress (Liu et al., 2017). Since there was no cortisol increase in either of the two experimental groups, we cannot draw any conclusion about the efficacy of the embrace unfortunately.

Our results have potential implications for everyday life situations since increases in glucocorticoids have been shown to impair memory retrieval and executive functioning

(McCormick, Lewis, Somley, & Kahan, 2007; Shields, Bonner, & Moons, 2015; Shields,

Sazma, & Yonelinas, 2016; Wolf, 2017). Memory traces that have not yet been fully consolidated and are therefore primarily -dependent show impaired retrieval under higher cortisol levels, especially if they have a negative (Merz, Hagedorn, &

Wolf, 2019). However, there is also evidence that non-hippocampus-dependent memories cannot be retrieved as effectively after exposure to acute stress (Atsak et al., 2016; Guenzel,

Wolf, & Schwabe, 2013). Since everyday situations like an upcoming examination are associated with a pronounced cortisol increase (Ringeisen, Lichtenfeld, Becker, & Minkley,

2019), it is important to consider potential buffers against the negative effects of cortisol secretion on memory retrieval. In contrast to long massages as performed for example in

19 Ditzen et al. (2007), a short-term embrace could be considered highly feasible method in everyday life to buffer against these effects based on the findings of our study.

In contrast to our hypotheses, we did not observe any changes in sympathetic nervous system activity indicated by the absence of group difference in blood pressure, regardless of sex.

Both in the studies of Meier et al. (2020) and Ditzen et al. (2007) prolonged exposure to social touch resulted in reduced sympathetic nervous system activity indicated by decreased heart rates or increased high-frequency heart rate variability. While it could be speculated that the effect of social touch on sympathetic activity might be selective for changes in heart rate, results from animal studies have shown that arterial pressure is also reduced by the injection of oxytocin (Petersson, Alster, Lundeberg, & Uvnäs-Moberg, 1996; Petty, Lang, Unger, &

Ganten, 1985). A more likely explanation why we could not observe changes in blood pressure could relate to the time course of our experiment. The SECPT in our experiment took place immediately after the embrace. The very quick succession of the SECPT might have prevented the buffering effects of oxytocin to take effect as the blood concentration could have been too low at this point in time. Another possible explanation could relate to the associated with the SECPT that strongly engages the sympathetic nervous system and is thus difficult to reduce.

Our study is subject to a few limitations that need to be acknowledged. First, while our sample size was generally adequate to observed between-subject effects, the comparison between the experimental conditions in free-cycling women contained only a rather small number of participants ultimately. Thus, it cannot be excluded that the observed effects here could be overestimated due to the small sample. We are however convinced that the reported effects are not false positives due to them being in concordance with the literature and the effect being very strong (d = 2.71). It was unfortunately not foreseen that no effect could be measured in women using OCs. Future studies should perform similar experiments and

20 specifically focus on free-cycling women to consolidate our findings. Another limitation was the lack of an oxytocin measure which could have informed us about changes in oxytocin levels across the study, especially during the SECPT. It should be noted however that peripheral oxytocin levels have been called into question whether they provide accurate measurements for oxytocin levels in the brain where the HPA axis is regulated (McCullough,

Churchland, & Mendez, 2013).

In conclusion, we found a cortisol-buffering effect of embraces between romantic partners following a stress induction procedure. The effect was however specific to free-cycling women and did not occur in men. This finding could have implications for stress reduction in everyday situations that often induce stress like exams or job interviews.

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