Searching for health information online has become increasingly common, yet few studies have examined potential negative emotional effects of online health information search. We present results from an experiment manipulating the presentation of search results for common symptoms, which shows that the frequency and placement of serious illness mentions within results can influence perceptions of symptom severity and susceptibility of having the serious illness, respectively. The increase in severity and susceptibility can then lead to higher levels of negative emotional outcomes experienced-including feeling overwhelmed and frightened. Interestingly, health literacy can help reduce perceived symptom severity, and high online health experience actually increases the likelihood that individuals use a frequency-based heuristic. Technological implications and directions for future research are discussed.