Providing direct health and social care services for people who exhibit behaviours that challenge can be a highly stressful occupation. Existing literature has suggested that there is a need to develop further theoretical understanding of how work related stress can be reduced in professions that consist of providing care for people who exhibit behaviours that challenge. The aim for this study was to use a Classic Grounded Theory approach to develop a theoretical framework to illustrate a common issue that could influence work related stress levels experienced when managing behaviours that challenge in health and social care settings. A series of focus groups and 1:1 semi-structured interviews were conducted to explore the articulated experiences of 47 health/social care professionals who provide care for people who exhibit behaviours that challenge. This led to the development of Therapeutic Engagement Stress Theory (TEST), which illustrates that the perceived capacity to therapeutically engage with people who exhibit behaviours that challenge is an issue that can influence the levels of stress experienced by health/social care professionals. TEST provides a framework that could be applied to identify specific factors that inhibit staff to successfully deliver caring interventions for people who exhibit behaviours that challenge, and also inform bespoke support mechanisms to reduce stress in health/social care professionals.