Causes of Cancer Causes of cancer are diverse and often involve a mix of genetic, lifestyle, and environmental factors. The most common causes of cancer include tobacco use, poor diet, exposure to carcinogens, chronic infections, and inherited gene mutations. Genetic mutations are at the heart of all cancers. These changes in DNA can be inherited or acquired. Inherited mutations — such as those in the BRCA1 or BRCA2 genes — significantly raise the risk for certain cancers like breast or ovarian cancer. However, most mutations are acquired during a person’s life due to external influences or random cell errors. Tobacco is the leading preventable cause of cancer globally. It contains dozens of known carcinogens and is strongly linked to lung, throat, mouth, pancreas, and bladder cancer. Even second-hand smoke exposure increases risk. Diet and lifestyle are major contributors. Diets high in red or processed meats, low in fibre, and lacking fruits and vegetables may increase cancer risk. Obesity is linked to at least 13 types of cancer, including breast, liver, and bowel cancer. Lack of physical activity, excess alcohol, and chronic stress can also contribute to a cancer-friendly environment in the body. Environmental exposures such as ultraviolet (UV) radiation from the sun can cause skin cancer, while substances like asbestos, radon gas, and industrial chemicals are known to increase risk for lung and other cancers. Causes of Cancer Infections play a role in several cancers. For example, human papillomavirus (HPV) is linked to cervical and throat cancers, while hepatitis B and C viruses are major causes of liver cancer. Helicobacter pylori infection is associated with stomach cancer. Hormonal influences, especially in hormone-sensitive cancers like breast or prostate cancer, may also affect risk. Long-term use of hormone replacement therapy (HRT) or contraceptives is a potential factor in some cases. Understanding the causes of cancer helps guide prevention strategies such as vaccination (e.g. HPV or hepatitis B), healthy lifestyle choices, regular screenings, and avoiding carcinogenic exposures. [Next: Symptoms of Cancer →]