This thesis is comprised of four studies that investigated context collision, the blurring between private and professional lives, for health professionals with personal Facebook profiles. The first and second studies explored the perspective of health professionals through online surveys. Seventy-two percent of veterinarians had a personal Facebook profile. Veterinarians with Facebook profiles were 2.91 times as likely to think it acceptable to post comments about work (24%) compared to those without. One in five veterinarians thought it acceptable to post comments about clinical cases. Seventy-seven percent of public health professionals (PHPs), had a personal Facebook profile. Although PHPs reported being unlikely to disclose personal information on Facebook, some thought it acceptable to: vent about the general public (15%) or post comments about those whose ideas challenge public health views (e.g., anti-vaccination proponents), (26%). Awareness of consequences was associated with lesser self-disclosure, while the need for popularity was associated with more self-disclosure, on Facebook. In the third study, a controlled field trial, “transparent” versus “ambiguous” workday frustration comments, posted to a mock health professional’s Facebook profile, resulted in lower credibility ratings from members of the Canadian public (p < 0.001). Credibility ratings were responsible for 82% of participant willingness to become a client of the mock physician or veterinarian profile owner, and 27% of participant willingness to accept advice from the mock PHP profile owner. In the final study, members of the general public and of various health professions (in separate focus groups) described and discussed impressions and impacts of workday frustration comments on Facebook, and of health professionals who post them. Both groups understood and empathized with workday frustration comments, and some viewed them as normal Facebook behaviour. However, impressions of health professional credibility (trustworthiness, caring and competence) were largely negatively impacted by the comments. This thesis provides evidence that will further inform e-professionalism guidelines. It describes positive and negative impacts to professionalism, credibility, and health relationships, resulting from the personal use of Facebook by health professionals, specifically with respect to workday comments.