Social media like Facebook are harshly criticized for the propagation of health misinformation. Yet, little research has provided in-depth analysis of real-world data to measure the scale of the phenomenon. This article examines an emblematic case of online health misinformation: the Facebook page Santé + Mag, which generates five times more interactions than the combination of the five best-established French media outlets. Based on the literature on cultural evolution, we hypothesized that its huge success can hardly be explained by the misleading nature of its content (H1) but rather by its diffusion of posts containing cognitive attractors that tap into evolved cognitive preferences, such as information related to sexuality, social relations, threat, disgust or negative emotions (H2-6). Drawing from media studies findings, suggesting that Facebook is primarily used to connect with friends and family, we hypothesized that the popularity of Santé + Mag could be driven by Internet users’ desire to strengthen their relationships by sharing phatic posts (i.e. statements with no practical information aiming at engaging or maintaining social interactions such as “hello”) (H7).To test these hypotheses, we examined 500 posts, along with their 6.5 million interactions and tracked the presence of misleading health contents, psychological attractors, and phatic posts. Our analyses showed that most posts were related to social relations, that only a quarter consisted of health misinformation, and that despite their emphasis on threat, they were negative predictors of interactions. Phatic posts, composed of short sentences such as “Sister I love you”, were the strongest predictor of interactions, followed by posts with a positive emotional valence. Sexual contents negatively predicted interactions and other cognitive attractors such as disgust, threat or negative emotional valence did not predict interactions. These results strengthen the idea that Facebook is first and foremost a social network used by people to foster their social relations, not to spread online misinformation. We encourage researchers working on disinformation to conduct finer-grained analysis of online contents and to adopt interdisciplinary approach to study the phatic dimension of communication, together with positive contents, to better understand the cultural evolution dynamics of social media.