Online communication channels provide people with a vast amount of information from different sources. Health influencers on social media are one of the sources that people use to gain health information and support regarding health-related issues; they are people with different backgrounds and expertise that social media users follow and perceive to be experts in that field. This qualitative case study employs content analysis to analyze videos of three health influencers and explore the kind of expertise that each case communicates to their followers. Videos are analyzed based on an analytical framework that looks into Syntactic, thematic and rhetorical structures to explore how they frame their messages in order to be perceived as experts. The study detected three different kinds of expertise who have different styles in communicating their expertise and in framing their messages: the informative awareness expert, the self-referential expert and the practitioner expert. Further details on the different and common framing styles each expert used is discussed in this thesis. Analyzing expertise online provided an insight on health influencers characteristics and their strategies to perform their expertise. It also suggests the kind of health information seekers who could be interested in this kind of expertise. The research results provide insights on regulating the potential effects of health influencers online.