Hair follicle stem cells, the tissue-specific adult stem cells that generate hair follicles, are also the cells of origin for cutaneous squamous cell carcinoma, a common skin cancer. Hair follicle stem cells cycle between periods of activation, during which they can grow, and quiescence, when they remain dormant. Using mouse models, we applied known cancer-causing genes to hair follicle stem cells, and found that during cell quiescence, hair follicle stem cells could not initiate squamous cell carcinoma. Once the hair follicle stem cells were in their active period, cancer growth began. Furthermore, we found that Pten, a gene important in regulating the cell’s response to signaling pathways, mediated tumor suppression via adult stem cell quiescence. Understanding cancer suppression through quiescence could better inform preventative strategies in patients susceptible to squamous cell carcinoma. This study also may reveal parallels between squamous cell carcinoma and other cancers in which stem cells have a quiescent phase.