IntroductionTobacco-related content is prevalent on social media, yet many methods of measuring exposure are inadequate due to the personalized nature of online marketing. The purpose of this paper is to examine the association between exposure to pro-tobacco messages (both industry-sponsored and user-generated) and the use of tobacco products, as reported via ecological momentary assessment (EMA). MethodsYoung adults (n = 175) were instructed to record all sightings of marketing (both in-person and online) related to tobacco for 28 days. Tobacco product use and recall of message encounters were assessed daily using app-initiated EMA. ResultsParticipants who reported exposure to tobacco messages were significantly more likely to report using tobacco, adjusting for gender, age, race/ethnicity, baseline use of any tobacco product, and having friends who use tobacco and e-cigarettes (p <.001). For each industry-sponsored message viewed, the odds of using tobacco or e-cigarettes in a given day increased by a factor of 1.77 (95 % CI = 1.41, 2.23). For each user-generated message viewed, the odds of using tobacco or e-cigarettes in a given day increased by a factor of 1.52 (95 % CI = 1.27, 1.83). DiscussionTo our knowledge, this is the first study to specifically examine the association between exposure to user-generated messages and daily tobacco use. The findings suggests that there is a unique element to user-generated messages that distinguishes them from both traditional marketing and from simple peer influence.