Smoking tobacco is a leading preventable cause of cancer worldwide. Each puff introduces a complex mixture of harmful substances into the body, initiating processes that can lead to uncontrolled cell growth and tumor formation.
How Smoking Causes Cancer
Tobacco smoke contains over 7,000 distinct chemical compounds. At least 70 of these are recognized as carcinogens, including substances like benzene, formaldehyde, arsenic, cadmium, and polycyclic aromatic hydrocarbons (PAHs). When inhaled, these chemicals enter the bloodstream and circulate throughout the body, reaching various organs and tissues.
The primary mechanism by which carcinogens lead to cancer involves damaging the body’s DNA. DNA serves as the instruction manual for cell growth and function, and damage to its structure can lead to errors or mutations. For instance, chemicals like benzopyrene, a PAH, can bind to DNA, forming “adducts” that disrupt normal gene function and DNA replication. These mutations can then interfere with the precise control mechanisms that regulate cell division, causing cells to grow and multiply uncontrollably.
Beyond direct DNA damage, smoking also promotes cancer through other biological pathways. It induces chronic inflammation throughout the body, creating an environment that encourages cell proliferation and tumor development. Oxidative stress, caused by an imbalance between free radicals and antioxidants, also plays a role, further damaging cells and their genetic material. Smoking also weakens the body’s immune system, making it less effective at identifying and destroying cancerous cells.
Cancers Directly Linked to Smoking
Smoking is a confirmed risk factor for numerous types of cancer. Lung cancer has the strongest association, with nearly 9 out of 10 lung cancer deaths attributed to smoking or secondhand smoke exposure. People who smoke face approximately 25 times the risk of developing lung cancer compared to non-smokers.
Beyond the lungs, smoking significantly increases the risk for many other cancers. These include cancers of the mouth, throat (pharynx), and voice box (larynx), where exposure to carcinogens is direct. Esophageal cancer, which affects the tube connecting the throat to the stomach, is also strongly linked to smoking. The chemicals in tobacco smoke can also travel through the bloodstream and urine, impacting organs such as the bladder and kidneys, leading to increased risk of cancer in these areas.
Additional cancers for which smoking is a known cause include pancreatic cancer, stomach cancer, and colorectal cancer. Liver cancer and acute myeloid leukemia are also associated with tobacco use. For women, smoking raises the risk of cervical cancer. Secondhand smoke exposure also increases cancer risk.
Impact of Quitting on Cancer Risk
Quitting smoking offers substantial health benefits, significantly reducing the risk of developing and dying from cancer, regardless of age or how long one has smoked. The body begins to repair itself almost immediately after the last cigarette. Within minutes, heart rate and blood pressure start to drop.
After about 5 to 10 years of quitting, the risk for cancers of the mouth, throat, and voice box is halved. For bladder, esophageal, and kidney cancers, the risk declines within 10 years of cessation.
After 10 years smoke-free, the risk of dying from lung cancer is approximately half that of someone who continues to smoke. The risk for pancreatic cancer also decreases significantly. After 20 years, the risk of several cancers, including those of the mouth, throat, voice box, and pancreas, approaches that of a person who has never smoked. The added risk of cervical cancer is also cut by about half after 20 years.