<p>People who engage in non-suicidal self-injury (NSSI) report doing so largely to</p><p>manage overwhelming emotions. Prominent theories of NSSI argue that an amplified</p><p>emotional response system creates the context in which a person chooses to regulate their</p><p>emotions by engaging in NSSI. In line with these theories, people who engage in NSSI</p><p>consistently report greater global emotion reactivity and emotion dysregulation than do</p><p>controls. These global self-reports of emotional functioning also predict the onset and</p><p>cessation of NSSI, demonstrating their considerable utility in understanding the behaviour.</p><p>However, global self-reports provide an overall evaluation of one's average affective</p><p>experience and so are ill-suited to isolating precise alterations in emotional responding.</p><p>I first establish how best to assess NSSI (Study 1a and 1b). I then leverage</p><p>experimental affective science and individual differences methodologies to test whether NSSI</p><p>is characterised by a more reactive and intense emotional response to challenge, and/or</p><p>whether factors that help to create, modify, and later recall the emotional response are altered</p><p>in those who engage in NSSI compared with controls. Study 2 compared how young adults</p><p>with a past-year history of NSSI and controls subjectively and physiologically reacted to, and</p><p>recovered from, acute stress. Study 3 compared how young adults with a past-year history of</p><p>NSSI and controls subjectively reacted to both explicit and more ambiguous social exclusion.</p>