More and more brands are utilizing online word-of-mouth recommendations to promote their products and using product ingredients more widely in marketing communications. However, no research has explored how recommendation terms (ingredient vs. function) for functional products affects consumers' attitudes. Through one pilot study and four experiments, it was found that consumers hold the lay belief that “ingredient = professional.” For functional products, consumers' purchase intentions and product evaluations are higher when ingredient (vs. function) are labelled, with perceived trustworthiness playing a mediating role. In addition, the domain knowledge of the information sender moderates the focal effect. Theoretically, this research contributes to the literature on both lay beliefs and word-of-mouth marketing by proposing a new lay belief, and by exploring the effect of recommendation terms on consumers' attitudes. Practically, this research can guide marketers in the appropriate use of product ingredient for word-of-mouth marketing.