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By Mayo Clinic staffWhile doctors have an idea of what can put you at risk of cancer, the majority of cancers occur in people who don't have any known risk factors. Factors known to increase your risk of cancer include:
Your age
Cancer can take decades to develop. That's why most people diagnosed with cancer are 55 or older. By the time a cancerous mass is detected, it's likely that 100 million to 1 billion cancer cells are present, and the original cancer may have been growing for five years or more. While it's more common in older adults, cancer isn't exclusively an adult disease — cancer can be diagnosed at any age.
Your habits
Certain lifestyle choices are known to increase your risk of cancer. Smoking, drinking more than one drink a day (for women) or two drinks a day (for men), excessive exposure to the sun or frequent blistering sunburns, and having unsafe sex can contribute to cancer. You can break these habits to lower your risk of cancer — though some habits are easier to break than others.
Your family history
Only about 10 percent of cancers are due to an inherited condition. If cancer is common in your family, it's possible that mutations are being passed from one generation to the next. You might be a candidate for genetic screening to see whether you have inherited mutations that might increase your risk of cancer. Keep in mind that having an inherited genetic mutation doesn't necessarily mean you'll get cancer.
Your health conditions
Some chronic health conditions, such as ulcerative colitis, can markedly increase your risk of developing certain cancers. Talk to your doctor about your risk.
Your environment
The environment around you may contain harmful chemicals that can increase your risk of cancer. Even if you don't smoke, you might inhale secondhand smoke if you go places where people are smoking or you live with someone who smokes. Chemicals in your home or work place, such as asbestos and benzene, also are associated with an increased risk of cancer.