Given the many health applications that require users’ sensitive information, this thesis examineswhich interface design elements affect users’ trust. This study examines how coercive data collection practices, opt-out mechanisms and data input screen design influence initial trust formationand willingness to share sensitive health information. Drawing on trust theory from literature combined with research on dark patterns and deceptive design, this research uses a mixed-methodscomparative prototype evaluation design involving qualitative interviews and think-aloud protocolswith health app users (N=18, ages 18-40, Sweden-based) and two functional web-based prototypesrepresenting coercive and autonomy-supportive onboarding designs. The study focuses on understanding how design choices such as mandatory versus optional fields, opt-in versus opt-out consentmechanisms, and the visual presentation of data collection screens impact users’ perception oftrustworthiness in health applications. Findings indicate that mandatory fields and coercive designelements significantly reduce trust and increase negative emotional responses, while autonomysupportive designs elicited higher trust scores, greater positive effect, and a paradoxical increasein voluntary data disclosure. Findings from this research aim to provide evidence-based designrecommendations for health app developers seeking to build trust while collecting necessary userdata, and to inform regulatory discussions about ethical design practices in digital health.