Cigarettes contain over 7,000 different chemical compounds when tobacco burns. Among these, at least 69 are recognized as substances capable of causing cancer.
Understanding Carcinogens
A carcinogen is any substance or agent that can cause cancer. These agents work by interfering with the normal processes within cells. This interference can lead to uncontrolled cell growth and division, a hallmark of cancer. These substances typically cause changes to a cell’s genetic material or disrupt the mechanisms that control cell growth and death. While some carcinogens directly damage DNA, others may promote cancer indirectly.
Primary Carcinogens in Cigarette Smoke
Cigarette smoke contains over 60 identified carcinogens from various chemical classes. Some of the most significant include polycyclic aromatic hydrocarbons (PAHs), N-nitrosamines, aromatic amines, benzene, and aldehydes.
Polycyclic Aromatic Hydrocarbons (PAHs), such as benzo[a]pyrene, are formed during the incomplete burning of tobacco. These compounds cause DNA damage.
N-nitrosamines, particularly tobacco-specific nitrosamines (TSNAs) like NNK and NNN, are formed during the processing and burning of tobacco. They are associated with cancers of the lung, mouth, and pancreas.
Aromatic amines, including 4-aminobiphenyl and 2-naphthylamine, were once used in dye manufacturing and are now banned in some industrial applications due to their carcinogenic properties. 4-aminobiphenyl, present in cigarette smoke, is linked to bladder cancer. Benzene is a known carcinogen that can cause leukemia.
Formaldehyde, a chemical used to preserve dead bodies, is toxic to the airways and is a recognized carcinogen. Acrolein, formed from burning sugars in tobacco, irritates the respiratory tract and can contribute to heart damage. Metallic elements like cadmium, arsenic, and chromium are also found in cigarette smoke and are known to cause cancer.
Mechanisms of Cancer Development
Carcinogens in cigarette smoke initiate cancer development through several biological processes, primarily by damaging a cell’s DNA. Many of these carcinogens require metabolic activation by enzymes within the body to become highly reactive. Once activated, they can bind directly to DNA, forming structures known as DNA adducts.
These DNA adducts can lead to errors in the genetic code when cells divide, resulting in mutations. If these mutations occur in genes that control cell growth, such as tumor suppressor genes or oncogenes, they can disrupt normal cellular regulation. Such genetic changes can promote uncontrolled cell division, a hallmark of cancer.
Beyond direct DNA damage, cigarette smoke carcinogens can also interfere with the body’s natural DNA repair mechanisms. This inhibition allows damaged DNA to persist and accumulate, increasing the likelihood of permanent mutations. Chronic exposure to these carcinogens can also lead to sustained inflammation within tissues.
Prolonged inflammation creates an environment that supports abnormal cell growth and can further promote cancer development. Additionally, some carcinogens can induce epigenetic changes, which are modifications to DNA that do not alter the sequence but can change gene activity. These alterations can influence how genes are expressed, potentially contributing to the cancerous transformation of cells.
Health Consequences of Exposure
Exposure to carcinogens in cigarette smoke is directly linked to a wide range of cancers and other serious health issues. Lung cancer remains the leading cause of cancer death in both men and women globally, with cigarette smoking being responsible for approximately 9 out of 10 lung cancer deaths.
Beyond the lungs, smoking causes cancers in numerous other parts of the body. These include cancers of the mouth, throat, esophagus, and larynx, which are in direct contact with the smoke. The systemic absorption of carcinogens also leads to cancers of the bladder, kidney, pancreas, liver, stomach, colon, and rectum.
In women, smoking also increases the risk of cervical cancer. Furthermore, cigarette smoking is a significant contributing factor to acute myeloid leukemia. The impact of these carcinogens extends beyond cancer, significantly increasing the risk of cardiovascular diseases.
Smoking contributes to heart disease, stroke, and aortic aneurysms by damaging blood vessels and promoting the buildup of fatty material on artery walls. Chronic obstructive pulmonary disease (COPD), which includes emphysema and chronic bronchitis, is another major health consequence directly linked to long-term exposure to cigarette smoke and its carcinogens.