Guided by the health risk communication literature and the social identity model of deindividualization effects, this study examines whether and how concurrent exposure to health news articles and congruent/incongruent comments posted by anonymous others may affect news viewers' personal risk perception, societal risk perception, and intention to communicate about health risk issues. Two controlled experiments were conducted in Vietnam concerning two controversial health risk issues, including ear picking and child corporal punishment. Results showed a significant interaction effect between comments and perceived similarity on personal risk perception and societal risk perception, such that comments influenced both types of risk perception when viewers perceived that anonymous commenters were ingroup members. Results also indicated the joint effect of comments and perceived similarity on participants' intention to communicate, mediated by their personal risk perception and societal risk perception. Theoretical and practical implications were discussed.