Rationale

Safety behaviour represents a core feature of various mental disorders1 2 and is defined as ‘actions taken to prevent, avoid or escape a feared outcome’.3 In the narrower sense, this includes behaviours such as taking sedatives, not going to certain places without another person or always carrying a bottle of water. Furthermore, it comprises avoidance behaviours and checking behaviour (CB), which manifests in different ways depending on the respective disorder. The earliest descriptions of the latter can be found regarding obsessive–compulsive disorders (OCD).4 5

In OCD, CB is the most common compulsion6 and manifests, for example, as controlling the absence of potential sources of danger in one’s surroundings (eg, stove turned off to prevent fire, windows or doors locked to prevent burglary) or repetitive requests for reassurance from others.7 8 Closely related to this, CB in generalised anxiety disorder (GAD) is also described,9–11 but mainly in terms of interpersonal checking (ie, seeking reassurance from others, eg, before making decisions, when engaging in activities or asking a loved one if he or she is upset).8 12 While in OCD and GAD, checking primarily refers to objects, environment, relationships and achievement, in other disorders, the main focus of CB is one’s own body. Disorders with body-related CB include eating disorders (EDs),13 body dysmorphic disorder (BDD)14 and illness anxiety disorder (IAD).15 In EDs, that is, anorexia nervosa, bulimia nervosa and binge-eating disorder, CB expresses itself as inspecting one’s own body in terms of its weight or shape, and manifests in behaviours such as repeated weighing, measuring the circumference of body parts, inspecting one’s body or individual body parts in the mirror, seeking reassurance about one’s appearance and comparing it to others.13 16 CB in BDD is described as inspecting one’s perceived defect by looking at it in the mirror or other reflective surfaces (eg, shop windows, car mirrors) in a ritualistic way, taking photos, comparing it with other people (in real life, media, photos of oneself in the past), checking its size or contour by touching it with one’s fingers, and asking others for reassurance (eg, whether the perceived flaw has become worse or is adequately camouflaged).17–19 Whereas, checking in EDs and BDD refers to figure, weight or appearance, checking in IAD focuses on health. It manifests as repeatedly inspecting one’s body for signs of illness (eg, breast self-examination, lymph node palpation) or seeking reassurance from others about health and signs of a severe illness (eg, family, friends, healthcare physicians or alternative sources such as medical textbooks).15 20

Although CB refers to different domains (eg, weight, illness, safety of the environment) in all five disorders, cognitive-behavioural theories regarding the mechanism of action of checking are very alike7 21–24. Three central theoretical postulates are formulated in each case. First, it is proposed that CB is used primarily in order to gain relief from unpleasant emotional states.22 25 Relatedly, the second theoretical postulate states that CB is thought to have a negative affect-reducing function in the short term.17 For example in OCD, it is postulated by Rachman7 that people repeatedly check for safety in situations where they feel unsure about the absence of harm in order to gain relief from their indisposition, uncertainty and anxiety.7 In EDs, it is hypothesised that body checking reduces negative affect which is triggered, for example, by dysfunctional body-related information processing.22 For BDD, it is postulated that there is distress caused by physical appearance, which becomes very strong, for example, in social situations. CB, according to the theory, serves to reduce these unpleasant emotions (eg, fear, disgust, anger, shame) caused by appearance.23 By providing immediate short-term relief from unpleasant feelings, the third theoretical assumption is based on a learning theory mechanism.23 It is postulated that CB as a behaviour is negatively reinforced (ie, produces the absence of a negative consequence), therefore increasing the likelihood that it will be performed more frequently in the future,22 as patients experience CB to be helpful and necessary in the short run. In contrast, theories postulate that repeated use of CB reinforces anxiety and psychopathology in the long term turning into a self-perpetuating mechanism.24 For example, it is discussed that CB can foster distorted perception and evaluation of one’s body in EDs.16 22 For BDD, it is postulated that CB increases selective attention in the long term and may intensify the dysfunctional beliefs about the supposed flaw(s), thus contributing to the maintenance of the disorder.17 19

In sum, although CB looks phenomenologically different depending on the respective disorder, aetiological models across disorders outline checking as an important behaviour, which provides immediate relief from negative states in the short term, therefore reinforcing itself and leading to a self-perpetuating mechanism, and hence contributing to the maintenance of the pathology in the long term. Although the mechanism of action of CB has been postulated in numerous models of different disorders, empirical support for these assumptions is lacking. To date, several empirical studies have investigated the proposed mechanisms in each disorder, but a systematic overview of studies is yet to be undertaken. A systematic overview, however, is urgently needed, given that current cognitive-behavioural treatments for these disorders are based on the afore-mentioned theories and include ritual prevention (ie, not using CB to learn that situations can be handled without this safety behaviour) as one therapeutic technique aimed at reducing CB and consequently related disorder-specific symptoms. Usually, this is addressed in the context of exposure therapy (ie, confronting patients with fearful or even avoided situations without the use of safety behaviours, eg, in OCD, leaving the house without checking the stove and windows). Depending on whether or not the empirical evidence supports the proposed emotion regulating mechanism of checking in the cognitive-behavioural models, the focus of these interventions would need to be intensified or altered, respectively. For example, one might assume that CB does not or not only serve to reduce negative affect but also to gain certainty.26 Therefore, it might be worthwhile to address the excessive need for certainty more directly, for example, through cognitive interventions questioning the pursuit of certainty27 or promoting the willingness to experience fear and uncertainty.28 Furthermore, a better understanding of the mechanisms of action underlying CB may also have implications for the prevention of mental disorders (eg, if the proposed long-term negative effect of CB on psychopathology can be supported by empirical evidence, prevention programmes addressing the reduction of checking in healthy individuals or at-risk groups could be developed).

Objectives

As such, our systematic review intends to synthesise existing evidence for the three postulates regarding CB across the mental disorders OCD, GAD, EDs, BDD and IAD. The current study protocol outlines the methods of our investigation and is based on the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols (PRISMA-P) checklist (online additional file 1). The following research questions will be addressed: (1) Which (emotional) states are people in when engaging in CB? (2) What effect does CB have on emotional, cognitive and disorder-specific outcomes in the short term (ie, directly following CB)? (3) What effect does CB have on emotional, cognitive and disorder-specific outcomes in the long term (ie, after a repeated number of checking episodes)?