Cancer develops when normal cells grow out of control. This usually happens because of genetic changes, especially mutations of genes that play a role in cell multiplication and repair.


Certain cancer risk factors can’t be controlled, including age and family history. Others, like smoking, are simple to avoid—but simple doesn’t necessarily mean easy! Some risk factors are influenced by a combination of genetics, environment and behavior. Finally, many cancers are attributable to random mutations that accumulate over time.



Smoking is responsible for around 30% of all cancer deaths in the United States. In addition to lung cancer, tobacco use can also contribute to a dozen other malignancies. Nicotine is addictive, and quitting smoking can be challenging. Some people find nicotine gum or patches, prescription medications or support groups helpful. The sooner you stop smoking, the better, but quitting is beneficial at any age.



Alcohol has been linked to cancers of the mouth and throat, esophagus, breast, colon, pancreas and stomach. Heavy drinking can cause cirrhosis, a major risk factor for liver cancer. The American Cancer Society recommends no more than two drinks per day for men or one drink per day for women.


Sun Exposure

Exposure to ultraviolet (UV) radiation from the sun or tanning beds is the major risk factor for skin cancer, including melanoma. Reduce exposure by staying out of the sun during midday and covering up with long sleeves and pants, a hat and sunglasses. Sunscreen with a high sun protection factor, or SPF, offers more protection, but even the best sunscreen doesn’t completely block all harmful radiation.


Diet and Exercise

A healthy diet and regular physical activity can reduce cancer risk. People with overweight or obesity are at higher risk for at least 13 different malignancies. The American Cancer Society recommends a well-balanced diet with plenty of vegetables, fruits and whole grains. Guidelines recommend that adults should get at least 150 minutes of moderate-intensity activity or 75 minutes of vigorous activity each week—but even brief exercise is beneficial.


Viral Infections

Some types of cancer are caused by viruses or bacteria. Human papillomavirus (HPV) is the main cause of cervical cancer, anal cancer and some oral cancers. HPV is commonly sexually transmitted, but it can also spread via nonsexual skin-to-skin contact. The Gardasil 9 vaccine protects against nine types of HPV. Guidelines recommend that adolescent girls and boys should be vaccinated at age 11 or 12, with eligibility continuing through age 27.


Hepatitis B and C, two blood-borne infections, are major causes of liver cancer. The Centers for Disease Control and Prevention now recommends the hepatitis B vaccine for all adults regardless of risk. There is no vaccine for hep C, but it can be treated with antiviral medications that cure most people in two or three months.


Cancer Screening

Regular screening can detect cancer early, when it is easier to remove or treat. Experts recommend routine screening for breast cancer, cervical cancer and colon cancer as well as regular visual exams for skin cancer. Lung cancer and liver cancer screening are recommended for people at high risk. Prostate cancer screening is offered for older men based on their individual risk factors and preferences.