Since the turn of the millennium, the potential for patients’ knowledge to contribute to medical knowledge has been increasingly recognized by medical sociologists and anthropologists. Where previously such knowledge may have been written off as 'beliefs' and assumed to be inaccurate when it contradicted established medical science, it is increasingly recognized that patients—especially those with chronic conditions—can add a valuable perspective to the clinical knowledge of medical professionals. Sometimes this means working together to reassess treatment priorities, and at other times it may mean a patient-led movement to influence the direction of new research, based on patients’ experiences. Ushiyama takes the case of eczema (atopic dermatitis)—a chronic condition with a history of patient-led controversy over treatment methods - as a case study in how patient knowledge has come to affect change in medical practice. Comparing ethnographic fieldwork from Japan and the UK, she builds a complex picture of the differences in approach to treatment in light of attitudes to patients’ knowledge.