It has long been known that excessive mitotic activity due to H-Ras can block keratinocyte differentiation and cause skin cancer. It is not clear whether there are any innate surveillants that are able to ensure that keratinocytes undergo terminal differentiation, preventing the disease. IKKα induces keratinocyte terminal differentiation, and its downregulation promotes skin tumor development. However, its intrinsic function in skin cancer is unknown. Here, we found that mice with IKKα deletion in keratinocytes develop a thickened epidermis and spontaneous squamous cell-like carcinomas. Inactivation of epidermal growth factor receptor (EGFR) or reintroduction of IKKα inhibits excessive mitosis, induces terminal differentiation, and prevents skin cancer through repressing an EGFR-driven autocrine loop. Thus, IKKα serves as an innate surveillant.