EGF and cutaneous squamous cell carcinoma: The aqueous extract of C. sudachi peel suppresses serum- and EGF-induced cell proliferation and enhances differentiation induction in keratinocytes through inhibition of the EGFR–ERK signaling pathway; thus, it may be effectively used for the prevention and treatment of skin diseases, such as psoriasis and cutaneous squamous cell carcinoma, caused by abnormalities in proliferation and differentiation in epidermal keratinocytes.