Emojis have become popular in online marketing communications. Marketers use emojis to humanize brand voice and elicit an emotional response from target audiences. However, little is known about how emojis are perceived and what kind of reactions they evoke. Therefore, this study aims to verify whether exposure to emojis leads to an increased intention to purchase and whether the use of emojis impacts campaign effectiveness in a real-life environment. In a theory build-up process, we draw upon the Dual Coding Theory and emotional contagion concept and develop seven hypotheses. We performed two data collection studies to test the hypothesized relations. The first study is based on a questionnaire (N=318), while the second is based on experimental design in a real-life business environment. Surprisingly, we found that using emojis had a negative effect on purchase intention, while the effect was positive when mediated by positive affect. Emojis increased the effectiveness of marketing campaigns for hedonic products and strongly impacted the return on advertising spent. The findings of this study have both theoretical and practical implications in the observed domains, particularly about the type of products emojis are most effective in promoting, gender differences, and real-life consumer behavior. This is the first study to use an experimental design in a real-life scenario to capture the role of emojis on campaign effectiveness and decipher the differences between genders and their perceptions of emojis. Theoretical and practical implications together with future prospects are discussed.