What causes somatic mutation?

Causes of somatic mutations may include but are not limited to:

• Endogenous factors: Endogenous factors encompass various types of errors that may arise in the DNA repair mechanism, during cellular replication or from exposure to reactive oxygen species (ROS) such as superoxides, hydroxyl radical, and peroxides during metabolic processes. 
• Cellular stressors: Cellular stressors include oxidative, nutrient, hypoxia, and genotoxic stresses that cause fluctuations in the cell or extracellular metabolic functions. The free radicals that are generated due to these fluctuations are harmful to DNA. 
• Chemical mutagens: Chemicals mutagens include several chemicals such as vinyl chloride, dimethyl nitrosamine (DMS), and ethyl methyl sulfate (EMS) among others, all of which alter or damage the structure of DNA. 
• Physical mutagens: Exposure to high energy radiations such as UV rays, X-rays, and alpha particles can sever nucleotide bonds or alter nucleotide sequences, which change the DNA structure.