Some other reasons

Exposure To Carcinogenic FactorsA) Ultraviolet light - Most of this is from sunlight. Actinic keratoses are most commonly seen in fair skinned individuals who are unable to tan and is associated with an accumulated lifetime exposure to sun.B) Ionizing radiation such as radiotherapy may also increase of skin cancers.C) Chemicals such as arsenic increase the risk of skin cancers.D)Both epidemiologic observations and molecular biologic characteristics of the tumor cells suggest UV light is sufficient by itself to induce AK. Sensitivity to UV light is inheritedE)Immunosuppression following organ transplantation dramatically increases the risk of developing Actinic KeratosisF)Genetic Syndromes -There are a number of rare genetic syndromes that increase the risk of skin cancers.