A vast amount of health information has been published online, yet users often report difficulties in locating information in this particular domain. Based on our prior research, we consider four categories of online health information seekers who demonstrate mixed information needs. Although their searching needs are often well satisfied by entering keywords into search engines, their need to explore information is not so well supported, thus affecting their user experience and satisfaction. In this paper, we propose design principles for supporting the exploration of online health information. We present the rationale and the design process of a web app - Better Health Explorer - which is a proof-of-concept app tailored to health information exploration. This work contributes to the design of online health information systems as well as exploratory systems in general.