Despite the impact of social media use on women’s self-perception, research has less frequently explored social media’s impact on behavioral intentions. Further, most of the research in this area has taken into account social comparison as a mediating variable, despite the extent of our social comparison being closely related to sexual competition, which is infrequently considered. This study explored the relationships between women’s Instagram use, Instagram image exposure, cosmetics behavior and attitudes, sexual strategies, and a hypothetical cosmetics purchasing decision task in order to determine the impact of sexual strategies and social media use on cosmetics-related consumer intentions. Two hundred twenty women (Mage = 25) completed a series of measures to assess these variables, were shown cosmetics-related Instagram images (idealistic facial images, budget cosmetics, luxury cosmetics, or travel images), and then completed a hypothetical cosmetics purchasing task. Women exposed to luxury cosmetics images spent relatively more than the other groups on the luxury items in the cosmetics purchasing task. Regression further revealed that the predictors of hypothetical cosmetics purchases were real-life cosmetics behavior and attitudes, Instagram use, and intrasexual competitiveness. Thus, considering intrasexual competition is important for a complete understanding of the mechanisms by which Instagram use impacts women’s cosmetics purchasing behavior.