Recent research has documented how single facial features can trigger person categorization. Questions remain, however, regarding the automaticity of the reported effects. Using a modified flanker paradigm, the current investigation explored the extent to which hair cues drive sex categorization when faces comprise task-irrelevant (i.e., unattended) stimuli. In three experiments, participants were required to classify target forenames by gender while ignoring irrelevant flanking faces with and without hair cues. When present, hair cues were either congruent or incongruent with prevailing cultural stereotypes. The results demonstrated the potency of category-specifying featural cues. First, flanker interference only emerged when critical hair cues were present (Experiment 1). Second, flankers with stereotype-incongruent hairstyles (e.g., men with long hair) facilitated access to information associated with the opposite sex (Experiment 2), even when the flankers were highly familiar celebrities (Experiment 3). The theoretical implications of these findings are considered. Copyright © 2009 John Wiley & Sons, Ltd.