Tobacco smoking is the number one cause of cancer worldwide. It accounts for 15.1% of all new cancer cases globally, more than any other single risk factor. In the United States, cigarette smoking causes about one out of every three cancer deaths. But smoking is just the largest piece of a broader picture: nearly four in ten cancers worldwide are linked to risk factors people can actually change.
Why Smoking Leads the List
Of the 18.7 million new cancer cases diagnosed globally in 2022, roughly 7.1 million (37.8%) were tied to 30 modifiable risk factors. Smoking alone was responsible for a larger share than any other factor at 15.1%, followed by infections at 10.2% and alcohol at 3.2%. The gap between smoking and the second-place cause is substantial, which is why public health agencies have focused on tobacco control for decades.
Smoking doesn’t just cause lung cancer. It raises the risk of cancers in the mouth, throat, esophagus, stomach, pancreas, kidney, bladder, and cervix, among others. The damage comes from thousands of chemicals in tobacco smoke that directly alter DNA in cells throughout the body, not just in the lungs. Men carry a disproportionate share of this burden: 45.4% of all male cancer cases in 2022 were attributable to modifiable risk factors, compared to 29.7% in women, largely because of higher smoking rates among men.
Infections Are the Second Largest Cause
An estimated 2.2 million new cancer cases each year are caused by infections, representing about 13% of all cancers (excluding non-melanoma skin cancers). Four pathogens account for more than 90% of these infection-related cancers: the bacterium that causes stomach ulcers (H. pylori), high-risk strains of HPV, and the hepatitis B and C viruses. HPV drives nearly all cervical cancers plus a growing number of throat cancers. Hepatitis B and C cause most liver cancers. H. pylori is the primary driver of stomach cancer.
What makes infections notable as a cancer cause is that many of these cases are preventable through vaccination and treatment. HPV vaccines and hepatitis B vaccines already exist, and H. pylori can be eliminated with a short course of antibiotics. In countries with strong vaccination programs, infection-related cancers are declining.
Alcohol’s Underappreciated Role
Alcohol contributed to an estimated 4.1% of all new cancer cases globally in 2020. That may sound modest, but it translates to hundreds of thousands of diagnoses each year. Alcohol is linked to cancers of the breast, colon, rectum, liver, esophagus, and mouth. The risk increases with the amount consumed, and there is no “safe” threshold for cancer risk. Even moderate drinking raises the odds slightly, though heavy drinking raises them substantially.
Excess Weight and 13 Cancer Types
Being overweight or obese is associated with a higher risk of 13 types of cancer, and those 13 types together make up 40% of all cancers diagnosed in the United States each year. The list includes cancers of the colon, rectum, breast (after menopause), uterus, kidney, liver, pancreas, ovaries, thyroid, gallbladder, upper stomach, esophagus, and a type of brain cancer called meningioma, plus the blood cancer multiple myeloma.
Excess body fat promotes cancer through several pathways. Fat tissue produces hormones like estrogen and insulin at higher levels, which can fuel cell growth. It also creates chronic low-grade inflammation that damages DNA over time. The CDC notes that these statistics are based on cancer type and do not estimate the exact proportion of each cancer caused by obesity. Still, maintaining a healthy weight is one of the most impactful things a person can do to lower overall cancer risk.
UV Radiation and Skin Cancer
More than 80% of melanoma cases worldwide in 2022 were caused by ultraviolet radiation exposure, roughly 267,000 out of 332,000 cases. In Australia, New Zealand, northern Europe, and North America, that figure climbs above 95%. Men are slightly more affected (86%) than women (79%), possibly due to differences in sun exposure habits and sunscreen use. Melanoma is the most dangerous form of skin cancer, but non-melanoma skin cancers caused by UV exposure are even more common, adding millions more cases globally.
Environmental and Workplace Exposures
Radon, a naturally occurring radioactive gas that seeps into homes through foundations, is responsible for about 21,000 lung cancer deaths every year in the United States. Around 2,900 of those deaths occur in people who have never smoked. The EPA recommends testing your home and taking corrective action if radon levels reach 4 pCi/L or higher.
Workplace exposures to carcinogens, including asbestos, diesel exhaust, silica dust, and certain chemicals, account for an estimated 2% to 8% of all cancers in high-income countries. One detailed analysis in Great Britain estimated that 5.3% of all cancers were caused by past occupational exposures, with men affected at more than three times the rate of women (8.2% versus 2.3%), reflecting the industries where these exposures are most common.
Genetics vs. Environment
Only about 1% of cancers are caused by inherited cancer syndromes, and up to 5% result from high-impact single-gene mutations. The vast majority of cancers arise from a combination of environmental exposures and random DNA copying errors that accumulate over a lifetime. Overall, about 80% of cancers are related to environmental factors in the broadest sense, including everything from smoking and diet to infections and pollution. Genetic factors contribute an estimated 26% of overall cancer risk, but that includes the many small genetic variations that influence how your body handles carcinogens, repairs DNA, or regulates cell growth, not just the dramatic inherited mutations like BRCA.
This balance between genes and environment is actually encouraging. It means that most cancer risk is not fixed at birth. The 37.8% of cancers tied to modifiable risk factors represent millions of cases each year that could, in principle, be prevented through changes in behavior, public health policy, and environmental regulation.