This study examines the nature of peer-to-peer interactions in public online comment spaces. From a theoretical perspective of boundary-work and expertise, the comments posted in response to three health sciences news articles from a national newspaper are explored to determine whether both scientific and personal expertise are recognized and taken up in discussion. Posts were analysed for both explicit claims to expertise and implicit claims embedded in discourse. The analysis suggests that while both scientific and personal expertise are proffered by commenters, it is scientific expertise that is privileged. Those expressing scientific expertise receive greater recognition of the value of their posts. Contributors seeking to share personal expertise are found to engage in scientisation to position themselves as worthwhile experts. Findings suggest that despite the possibilities afforded by online comments for a broader vision of what peer-to-peer interaction means, this possibility is not realized.