This study explored perceptions of micro social media influencer (SMI) authenticity, an emerging area of research. Micro SMIs create intimate connections with their followers, which makes them attractive to brands. However, how followers, rather than brands, perceive SMI authenticity is an emerging research area. To address this research gap, 6508 comments on micro fashion SMIs’ posts were downloaded and analysed utilising thematic analysis. The results found that followers used the micro fashion SMI’s appearance, including their clothing choices, to establish their authenticity in their content and posts. This was the same for sponsored and non-sponsored posts. Thus, regardless of whether the micro fashion SMI was being paid for their content or not, followers appeared to perceive their authenticity in the same way. The results contribute to understandings of the authenticity of micro SMIs’ and have practical implications for micro fashion SMIs and the brands that may wish to employ them.