ObjectivesSelf‐affirmation approaches for health behaviour demonstrate consistent small to medium effects on message acceptance, health intentions and behaviour change. There are several forms of self‐affirmation (e.g., values affirmations, implementation intentions), but few empirical comparisons to guide selection in empirical work. Further, there has been little emphasis on the putative mechanisms of self‐affirmation driving behaviour change. The current investigation compared a control and four self‐affirmation approaches: values, social, implementation intention, and perspective taking.MethodsParticipants were recruited through CloudResearch (N = 666) and reported baseline sun exposure and protection behaviour at Time 1. One week later (Time 2), returning participants (N = 535) were randomly assigned to condition, viewed a message conveying risks of sun exposure, and reported sun exposure and protection intentions for the next week. Follow‐up one week later (Time 3; N = 449) assessed past week sun exposure (i.e., number of days spent outside during peak hours), sun protection behaviour (e.g., sunscreen use), future sun exposure and protection intentions and engagement with resources conveying further health information (i.e., viewing infographics, following links to websites with more information). The association of putative mechanisms with self‐affirmation conditions and health outcomes was also examined.ResultsUnexpectedly, there were few differences between self‐affirmation conditions and the control on intentions, information seeking, or behaviour at follow‐up. At follow‐up, perspective circle participants reported fewer days spent outside, spent longer viewing infographics, and, along with social values participants, followed more weblinks seeking information than control participants. The putative mechanisms were unrelated to health outcomes.ConclusionsThe current investigation was a first step in comparing novel online self‐affirmation approaches and had largely null findings. Results suggest that the perspective circle performed best at promoting information seeking and, to some extent, behaviour change. Suggestions for future directions are discussed.