Existing research often interprets the limited impact of candidate gender on vote choice as evidence of minimal gender bias in politics. However, this overlooks the dual role of candidate gender, as both a heuristic for substantive representation and a trigger for sexism in voter decision-making. These competing mechanisms can diminish the effects of each other, obscuring the true influence of gender bias in electoral behavior. Using conjoint experiments in South Korea, a context where gender issues are highly politicized and sexism remains widespread, we examine how candidate gender affects voter evaluations in low- and high-information environments. Our findings reveal that in low-information settings, candidate gender serves as a cue for substantive representation, leading to co-sex voting among women, while simultaneously activating hostile sexism among male voters, reducing support for female candidates. In high-information settings, explicit candidate policy positions diminish the reliance on gender cues but do not eliminate gender bias. Instead, sexism manifests through opposition to gender-equity policies rather than direct discrimination against female candidates. These results suggest that information environments shape the expression of gender bias, rather than eliminating it, offering a more nuanced understanding of the conditions under which candidate gender influences electoral preferences.