Indoor tanning (IT) increases the risks of skin cancer, but evidence on how to design health education messaging targeting IT among young adult women remains limited. This study investigated the effects of theory-guided gain-, loss-, and balanced-framed IT prevention messages. Young adult women ages 18–30 who indoor tan (n = 552, mean age = 24.9 years [standard deviation = 3.1]) were recruited online, completed pre-exposure measures, and were randomized to view a gain-, loss-, or balanced-framed message. Participants completed post-exposure measures of message response (emotional response, message receptivity), IT risk (perceived severity, susceptibility), and efficacy (self-efficacy, perceived benefits of avoiding IT) beliefs, and IT behavioral intentions. Loss- and balanced-framed messages promoted significantly greater emotional response and message receptivity and lower IT behavioral intentions than gain-framed messages. The effects of loss- and balanced-framed messages on IT behavioral intentions were mediated by greater emotional response and message receptivity compared with the gain-framed message. These results can inform the development of public health education campaigns to prevent and reduce IT among young adult women. Future research can build from these findings by investigating additional message themes and tailoring strategies to maximize their effects, examining the effects of framed messages prospectively, and investigating ways to enhance message receptivity, such as through novel message delivery channels (e.g., mobile devices).