Even exposure to the ill-defined term “fake news” and claims about its prevalence can be harmful. In an experimental study among respondents from Mechanical Turk, Van Duyn, and Collier (2019) find that when people are exposed to tweets containing the term “fake news,” they become less able to discern real from fraudulent news stories. Similarly, Clayton et al. (2019) find that participants from Mechanical Turk who are exposed to a general warning about the prevalence of misleading information on social media then tend to rate headlines from both legitimate and untrustworthy news sources as less accurate, suggesting that the warning causes an indiscriminate form of skepticism.
That is from Brendah Nyhan’s good new JEP survey article on how misperceptions come about and persist.