Tehran University of Medical Sciences Iranian Journal of Public Health 2251-6085 51 11 2022 11 09 2382 2387 Dariush Farhud 1. School of Public Health, Tehran University of Medical Sciences, Tehran, Iran 2. Research Institute of Aging, Tehran University of Medical Sciences, Tehran, Iran 3. Department of Basic Sciences, Iranian Academy of Medical Sciences, Tehran, Iran 2022 11 09 Almost all diseases have a genetic basis. However, several disorders stem from a combination of genes and environmental conditions. In the present study, databases including PubMed, Scopus and Google scholar were searched and reviewed and those relevant studies that investigated the association between environmental and genetic factors with the incidence of diseases were extracted and used. At the final step, it is concluded that in many cases, disorders have a multifactorial etiology. Having a gene related to a specific disorder is not the only reason for contracting the disease. Both genes and environmental factors play a role in human disease etiology. Everything outside of DNA, may affect health and even in many people with a positive family history of a specific disorder, environmental factors can facilitate or prevent the occurrence of the disease. Therefore, living a healthy lifestyle is important in reducing exposure to diseases, and long-life expectancy.   https://ijph.tums.ac.ir/index.php/ijph/article/view/30336 https://ijph.tums.ac.ir/index.php/ijph/article/download/30336/7764