What is ‘normal’ health? The way health scientists answered this question changed in the twentieth century, as they relied more heavily on social categories to measure health. These categories, sometimes termed reference- classes, rely on parameters such as age/weight/height/sex/gender/race/class. They still guide how providers distribute care and decide who deviates from ‘normal’ enough to count as disabled. Genetic research provides crucial theoretical scaffolding that legitimates their use. This project will demonstrate how proof of inheritance was established in genetic disability research and how proof of injury/illness was demonstrated in compensation cases. It investigates which categories were used to establish disability causation and interrogates biases inherent to the understanding of ‘biological’ versus ‘social’ determinants of health. This project therefore moves beyond considering disability as normative, to question the extent to which the categories used to define it are normative. Considering disabled experiences and the use of categories in compensation moderation demonstrates the longer-term consequences of categorisation choices and shows how data has been used to obscure health inequalities related to society and the environment. My innovative interdisciplinary approach will reveal how both disability and eugenics relate to a history of categorizing inequality through obscuring the relationship between the environment and the individual. We think of categories like height, weight, and sex as integral to health assessment. My project examines how such categories were made integral over the twentieth century through genetic science, and how they worked to construe disability as either biological or social. My approach combines insights from disability history and history of science to examine the historical processes that constructed these categories. This is important because how these categories were constructed influenced subsequent provision for the disabled. When Categories Constrain Care uncovers the hidden damage categories used in healthcare can cause and reveals the socio-historical forces that have shaped how these categories were used. Making disability visible in the categorisation processes central to science will destabilise the personal health paradigm and invigorate our understanding of how the environment and the individual interact, addressing the needs of the first generation to have grown up aware that they carry recessive (disabling) genes.