Cancer remains enigmatic, as far as the causes are concerned. A correct list of causes cannot be charted out as it is a condition of multiple causes and reasons. However, several risk factors have been identified with cancer. As the risk factors are wide, complex and unavoidable in many cases, all are at risk of developing cancer! The major risk factors associated or linked with cause of cancer are discussed below. A chemical or physical factor identified as a risk factor capable of causing cancer is called a ‘carcinogen’. In general, more the exposure to a carcinogen is linked to greater risk of developing cancer.

Some of the prominent carcinogens are listed below:-

• Chemical Carcinogens:  
  1. Tobacco Smoke : A chemical compound called nicotine present in the tobacco plant has is one of the early carcinogen identified. Therefore, smokers and users of other forms of tobacco products are at risk of cancer, and hence it has been made mandatory to display warning messages on cigarettes packets. Smokers are likely to develop lung, mouth, oesophageal, throat, pancreatic and bladder cancer. But cancer in any other part also cannot be ruled out. Smoking is identified as one of the major risk factors of cancer throughout the world.
  2. Other Chemicals : Many chemical compounds we use in daily life are known carcinogens and the list is endless. But, for most of us, who handle them once in a while are at lesser risk, while who handle them or work on them are at greater risk. For example, asbestos, coal tars, benzene, aflatoxins, formaldehyde, etc. the list is huge and heterogeneous.
• Radiation: Radiation is another cause of cancer. Radiations from radioactive materials and nuclear fallout enhance the risk of development of cancer. Even too much exposure to sunlight is risky, as radiations lie the ultraviolet and infrared rays, present in the light are harmful and induce mutations in the skin cells and turn them to be cancerous. Exposure to radiations like X-ray, ultraviolet ray, etc for diagnostic or other medical purposes also is risky, if beyond the permissible limits and frequencies. Our daily use gadgets like the cell phones, laptops, etc. also are under watch for their health risks including cancer.
•  Age: Age is one of the important factors associated with cancer risk. As age advances, exposure to all the risk factors in the environment by the individual accumulate and may exert a cumulative effect. Meanwhile, the ability of the body to counteract such ill effects keeps a downtrend with age, as the immune mechanisms of our body get reduced. All repair and rejuvenation mechanisms of damaged cells may not work well and this ultimately results in cancer development.
• Lifestyle Factors: Diet and other lifestyle factors can also influence the risk factors associated with cancer and play a secondary role in cancer risk. For example, Eating plenty of fruits and vegetables avoids or diminishes the activities of certain destructive enzymes at cellular level causing cell damage and alterations in the genes. Regular physical exercise and good eating habits are considered to improve body immune mechanisms and hence help in warding off ill health in general, including cancer. Fat rich diet leading to obesity is thought to have a positive influence on cancer risk factors. Certain habits like smoking and alcoholism have been identified as high-risk factors in developing cancers of respiratory and digestive organs. Occupational hazards are another section of the lifestyle dependent risk to cancer. People working in chemical industries, manufacturing of asbestos, handling radiation instruments, researchers working on carcinogens, etc. are few examples of people facing such risks, as part of their occupation.
  
• Infection: Cancer can be developed due to the infection of certain viruses called oncoviruses. Common examples are hepatitis B virus, hepatitis C virus and human= papilloma virus (HPV) have been confirmed as predecessors of cancer. Hepatitis B and C infection are associated with liver cancer while HPV infection with cervical cancer. Apart from these, Epstein-Barr virus, herpes virus etc. represent some other examples.
  
• Immune System: Like any other disease, cancer is also prevented to a certain extent by the in-built defense mechanisms of our body called immune system. Therefore, people with a poor immune system show higher levels of risk towards certain cancers. People receiving immuno-suppressive therapy and those affected by immunodeficiency disorders like AIDS generally are more prone to develop cancer.
  
• Genetic Makeup: The genetic ‘make-up’ refers to the combination of different forms of genes which we inherit from our parents. Most of the genes in our cells have different forms called alleles. For example, the blood group gene has two alleles, called A and B, which give rise to 4 different blood types like A, B, AB and O, based on their presence/absence. Some forms of genes are more prone to alterations leading to cancer than others. This fact has been understood from the analysis of various childhood cancers.
  

Most Cancers are caused by combination of many factors

When we analyze the history of many cancer patients, we can easily make out that all of them may have one or more of the associated risk factors in them. For example, all smokers may not develop cancer and few non-smokers also be cancer patients. Similarly, a marginal number of patients may not have any of the cancer risk factors with them. Therefore, it is inferred that the real incidence of cancer among the people is due to the combination of more than one risk factors and /or failure of the counteracting defense mechanisms of the body.