Keratinocyte apoptosis can be triggered by a variety of factors including UV radiation, oxidative stress, and chemical agents. UV radiation is one of the most significant external factors leading to DNA damage, which can initiate apoptotic pathways. Internal signals such as cytokines and growth factor withdrawal also play a crucial role in signaling apoptosis. The intrinsic pathway, which involves mitochondrial outer membrane permeabilization, and the extrinsic pathway, initiated by death receptors, can both lead to apoptosis in keratinocytes.