An increased risk of breast cancer has been associated with light at night (LAN). Several risk factors have been identified that play a crucial role in causing most cancers such as the consumption of alcohol and smoking, and low fruit and vegetable intake. As a risk factor for cancer, environmental factors also play an essential role including indoor and outdoor air pollution. Light pollution has been found to be a risk factor for breast cancer in the form of artificial light at night, with melatonin being the mediator between environment and the epigenome. The risk of cancer in night shift workers can also amplify by artificial light at night. Light at night may also effects sleep disruptions and also considered as a risk factor of breast cancer.