Influencer advertising on Instagram effectively brings products to the attention of young, engaged audiences. Though brands often select Instagram influencers with green expertise for eco-friendly product endorsements, this study argues that generic lifestyle influencers are also suitable endorsers, expanding the reach to wider, more diverse young audiences. Advertising outcomes of a lifestyle influencer’s sponsored Instagram post were compared in three online scenario-based experiments using a 2 (eco-friendly vs. regular lifestyle product) × 2 (small vs. large influencer) between-subjects design. Building on schema incongruity theory, the first two experiments among female Instagram users between 18 and 25 years old confirmed our hypothesis that posts in which female lifestyle influencers promote eco-friendly (vs. regular) lifestyle products evoke more curiosity, which positively affects ad attitude and purchase intention. Conditional indirect effects consistently suggest that the relationship between product type and both ad attitude and purchase intention is only mediated through curiosity for large (vs. small) lifestyle influencers. The findings did not replicate in a third study featuring a male lifestyle influencer among male Instagram users between 18 and 34 years old. Hence, the proposed effects manifested only in the specific demographic of female emerging adults. Potential explanations and implications of these results are discussed.