DNA damage is described as any kind of alteration in the structure of the nucleic acid with a possibility of change in the function depending up on the severity of damage. Such alterations impact the viability and cellular machinery. Such damages turn out to be major reason for cancer and other tumours. A mutation originated from any DNA damage progresses further developing into a cancer. These DNA alterations can be induced through a wide range of physical and chemical mutagens. A cluster of mutations that activate cancer causing genes (oncogenes), inactivate suppressor genes and disturb genome stability pave path to cancer. With this reference, we consider the history of smoking in few individuals to briefly assess their DNA using comet assay. Comet assay traditionally described as ‘single cell gel electrophoresis’ assay is being employed to detect DNA strand breaks. The formation of ‘comets’ can be traced as there is variation in the migration of damaged DNA and non-damaged DNA. The assay comes up with advantages such as better sensitivity, quick application, and flexibility to perform but on contrary, it cannot detect mitochondrial DNA damage.