The principal cause of cancer is mutation, which can be caused by a number of things. It is impossible to live a life with 0% chance of developing cancer. Practically anything that interacts with DNA can cause cancer. Even though the human body is very well equipped to repair damage, issues usually arise when DNA is damaged repeatedly or when the body’s repair systems are not functioning properly. When cells repair damage it is likely a small portion of these mutations will be repaired incorrectly, perhaps the damaged DNA strand was mistaken as healthy and the other strand was changed to match it, perhaps the damage broke both sides of the strand leaving the cell without indication of the previous configuration (if any of this sentence did not make sense it is recommended to read the section on DNA HERE). If a cell repairs this damage in a way that leaves it different to the original but still structurally sound this damage becomes a permanent mutation. Cells often face around 100,000 DNA lesions each day(1). This research highlights how adept cells are at repairing damage. Some examples of causes to cancer include endogenous factors, inherited genetics carcinogens and radiation:
Endogenous factors. Not all cancers are impacted by any outside source. Epidemiology has shown that only about 70-80% of cancer cases require an exogenous component (2). DNA damage can occur due to endogenous factors such as reactive metabolites (byproducts created when the body breaks down various molecules) and hydrolysis (a common chemical process where water breaks down other molecules). These mutations can make genes more susceptible to other causes of cancer or be the entire cause of carcinogenesis (1).
Inherited genetics. Cancer itself cannot be passed down to children, however some may have genetics that increase the overall risk of cancer. These genes usually do not simply cause cancer, but rather inhibit or weaken the cellular processes to do with repairing/protecting DNA. A child only inherits half the genetic material from each parent, and only about 10% of cancers can be linked to an inherited gene. If concerned, talk to your doctor as there are genetic tests for these conditions and prophylactic treatments.
Carcinogenics. Carcinogenic is an adjective used to describe anything that has the potential to cause cancer. Everything in this list could be referred to as carcinogenic, (carcinogenic genes, carcinogenic endogenous processes, etc) however this section is specifically focusing on carcinogenic chemicals. There are a variety of substances that can interact with, and damage DNA. There are a number of commonly known sources such as cigarettes and asbestos and a huge amount of other lesser known examples. It is often hard to determine and prove something causes cancer as there are so many variables when studying the cause of cancer.
For example, smoking was popular throughout America for most of the twentieth century, and although a multitude of studies were conducted to investigate negative health effects of cigarettes, such as lung cancer, the cigarette industry was able to cast much doubt on the research due to it all being chance or correlation based. A direct and immediate causal link was only discovered late in the 20th century and without one, proving that high quantities of tobacco smoke, over a prolonged period of time, increased the risk of lung cancer was an annoyingly shaky position to convince the public of (3). For the record, this paper does not recommend tobacco consumption due to its addictive properties and the multitude of health risks that exposure can cause.
Other carcinogenics are currently under research, such as red meat. According to the World Health Organisation (WHO) red meat is currently classified as a group 2A carcinogen, this means that there is limited research and other causes/biases/variables could not be ruled out. With that said the WHO recommends limiting red meat consumption while also admitting that red meat has a variety of proven health benefits and no clear safe consumption level has been determined. All of this to say many things can have impacts on cancer and discerning when to actually adjust lifestyle choices can be hard to do effectively. (4)
Radiation. Some consider radiation or radioactive materials carcinogens but for the sake of articulation this paper will separate the 2 as they interact with DNA differently. Radiation is defined as energy moving in space or through a medium using particles or waves. This energy can damage DNA by altering the chemical structure, subtracting or adding energy to the complex web of bonds and forces in DNA can disrupt the entire structure causing mutations.
The most common type of radiation is electromagnetic radiation. Electromagnetic radiation is one of the only types of radiation people are likely to encounter everyday, meaning that it is also the only type of radiation people are likely to encounter without prior training, this can lead to a number of myths about the dangers of household appliances such as phones, microwaves etc. Electromagnetic radiation are waves of energy, depending on the frequency of the waves they are classified and used differently. Fig 1 shows different types of electromagnetic radiation. While things with lower energy such as visible light, infrared, microwaves and radio do not have enough energy to alter the structure of molecules (non ionizing), higher energy waves are able to (ionizing). Examples of ionizing energy include ultraviolet, X rays and gamma radiation are known causes of cancer as they have enough energy to alter DNA.
It is important to remember that in medical settings X rays and gamma rays are used for treatments and diagnosis. The risk of developing cancer from measured amounts of radiation within clinical settings are usually far outweighed by the benefits of such a procedure . Talk to your doctor if you are concerned about the risk of a procedure. (5)
Note: more on the use of radiation in diagnosis here. And more on the use of radiation in treatment here.
| 1. | De Bont R, van Larebeke N. Endogenous DNA damage in humans: a review of quantitative data. Mutagenesis. 2004;19(3):169-185. doi:10.1093/mutage/geh025 |
| 2. | Doll R, Peto R. The causes of cancer: quantitative estimates of avoidable risks of cancer in the United States today. Journal of the National Cancer Institute. 1981;66(6):1191-1308. Accessed July 11, 2026. https://pubmed.ncbi.nlm.nih.gov/7017215/ |
| 3. | National Center for Chronic Disease Prevention and Health Promotion (US) Office on Smoking and Health. Fifty Years of Change 1964–2014. Nih.gov. Published 2014. Accessed July 11, 2026. https://www.ncbi.nlm.nih.gov/books/NBK294310/ |
| 4. | World Health Organization. Cancer: Carcinogenicity of the Consumption of Red Meat and Processed Meat. World Health Organization. Published October 26, 2015. Accessed July 11, 2026. https://www.who.int/news-room/questions-and-answers/item/cancer-carcinogenicity-of-the-consumption-of-red-meat-and-processed-meat |
| 5. | Cancer Council. Can radiation from medical tests cause cancer? www.cancer.org.au. Accessed July 11, 2026. https://www.cancer.org.au/iheard/can-radiation-from-medical-tests-cause-cancer |