What Causes Cancer?

Cancer is something most of us will encounter in one way or another, whether personally or through someone we love. It’s a word that can feel frightening and overwhelming, often surrounded by uncertainty and misinformation. But understanding how cancer develops, what can influence our risk, and which factors are simply beyond our control can help make those conversations a little less daunting. This article explores the many different elements linked to cancer risk — from lifestyle and environment to genetics, infections and ageing — with the aim of informing rather than alarming. Knowledge cannot remove every risk, but it can help us make informed choices and approach our health with greater awareness and compassion.

What is Cancer?

There is DNA inside every single one of our cells. DNA is what stores genetic information, acts as a template for making proteins, and is used this in your body and passed on to the next generation. Everything needed to build, grow and maintain an organism is found within DNA. It’s the blueprint to life, and it’s what makes us, us!

But when the DNA inside some of our cells mutates and changes, their normal pattern of growth gets disrupted, and those mutated cells multiply uncontrollably fast, building into tumours and spreading the mutation throughout the body. That’s what cancer is. It’s damaged, fast-multiplying cells that spread, causing chaos wherever they end up.

Sometimes those DNA mutations happen naturally over time, while some are triggered by lifestyle choices, environmental exposures, genetics, or a combination, with some cancers being commonly caused by one thing, and others developing by chance. It’s difficult to predict, which is part of the problem.

Lifestyle

There are things that you do, or don’t do, in your day-to-day life that could influence your risk of developing certain kinds of cancer. These are things you can change or at least manage, and doing so can reduce your risk for cancer. These are things like:

Tobacco use: The single biggest cause of preventable cancers. Smoking is strongly linked to lung, throat and bladder cancers. It’s not just standard tobacco smoke either. Smoking marijuana also puts you at risk, since it contains many of the same carcinogenic chemicals that cause cancer.

Diet and obesity: Being overweight or having a poor, unbalanced diet has been linked to higher risks of at least 13 types of cancer, including bowel and breast cancer. This is because excess fat cells don’t just store energy for when the body needs it. They’re active organs that disrupt the body’s normal processes, which can lead to harmful changes that encourage cancer cells to develop and multiply faster.

Alcohol: The risk of mouth, throat, liver and breast cancer increases if you drink even a moderate amount of alcohol, and the risk increases the more you drink. Alcohol is classed as a Group 1 carcinogen because when your body metabolises it, it converts it into a chemical called acetaldehyde, which directly damages DNA and stops the body from repairing that damage. It’s a breeding ground for cancer cells.

Sun and UV exposure: UV (or ultraviolet radiation) exposure, either directly from the sun or from things like tanning beds, significantly increase your risks for developing various skin cancers, including melanoma. UV exposure not only damages skin cells, but it penetrates them down to the DNA, damaging that as well. The radiation triggers genetic mutations and damages the genes responsible for tumour suppression. It won’t happen from a one-off exposure, but that damage builds and ultimately causes cancers. That includes things like UV nail lamps too – UV is UV no matter where it comes from!

Genetic

Sometimes it’s not what we’re doing that’s the problem, it’s what we are. In some cases, cancer risk can run in families. Around 5-10% of cancers are considered hereditary, which doesn’t mean you will definitely develop them, but it does significantly increase your risk of it. For example, if you were to inherit specific mutations in the BRCA1 or BRCA2 genes, you’re much more likely to develop breast or ovarian cancer.  Lynch Syndrome is the most common cause of hereditary colorectal cancer (or bowel cancer) and increases your risk of womb, stomach, ovarian and pancreatic cancers. There are a few more, which is why if you’re diagnosed with a new condition, you should check if it’s linked to a hereditary cancer.

Environmental and Occupational

If that wasn’t enough, there are also certain substances and environments that are considered as carcinogenic, which means they contain cancer-causing agents. Thankfully there aren’t too many of them, but it’s always worth being aware of so you can avoid them!

Chemicals and toxins: Regular and prolonged exposure to certain materials can result in cancer. Some are linked to specific cancers, while others simply encourage the development of general cancers. For example, long exposure to airborne asbestos fibres is a known cause of several fatal cancers, including mesothelioma (which is incredibly rare and only really found in exposure to asbestos), laryngeal cancer and ovarian cancer. It even has a specific cancer named after it – asbestos-related lung cancer. Other materials known to cause cancer include arsenic, cadmium, formaldehyde or benzene.

Radiation: Just like with UV exposure, exposure to high levels of ionising radiation and X-rays can increase your risk of cancer. Ionizing radiation comes from decaying uranium in soil and rocks, and in most places the amounts are negligible. However, some places have higher concentrations, and testing should be done before you buy a property to make sure radon levels are low. For X-Rays, doses are incredibly low, and the amount of radiation varies depending on the type of A-ray and the area of the body being imaged. But as a ballpark, you would need thousands of them to cause any significant increase in your risk of cancer.  

Air pollution: Breathing in contaminated air has been linked to various types of cancer, including lung and liver cancer. That’s because polluted air contains a number of mutagens and carcinogens, which are compounds that are known to mutate or damage DNA, or generate something called DNA adducts, which is a piece of DNA that’s bound to a cancer-causing chemical.

Infections and Medical Conditions

Finally, there are some infections and medical conditions that can heighten your risks too. Those feel like adding insult to injury, and thankfully they are few and far between, but they do still exist. And medical researchers are working hard to find ways to prevent them, or at least reduce the risk.

Viruses: Certain infections increase your risk of certain types of cancer. For example, HPV (Human Papillomavirus) causes cervical cancer, and the NHS does now offer a vaccine to reduce the risk to anyone 12 and over. Hepatitis B and C can both cause liver cancer, and while there is a vaccine for Hepatitis B, there isn’t currently one for Hepatitis C.

Immune system issues: Having a supressed immune system (like from HIV, organ transplants or immunosuppressants) increases your susceptibility to specific cancers, including Kaposi Sarcoma, cancers that are driven by viruses(like Non-Hodgkin Lymphoma, which is strongly linked to Epstein-Barr Virus), and aggressive forms of skin cancer.

Sadly there is one thing that’s the single most significant risk factor for most cancers, and that’s age. The longer you live, the more time your cells have to accumulate damage and mutations. So as you get older, your risk profile for cancer naturally goes up, which is why there are so many screening programmes and proactive tests available.

Cancer is incredibly complex, and there is rarely one single reason why it develops. Some risk factors can be reduced through everyday choices, while others are inherited or simply part of getting older. That uncertainty can feel unsettling, but it’s important to remember that reducing risk is not about striving for perfection or living in fear. Small, consistent acts of care toward your body and mind can still make a meaningful difference over time.

Looking after yourself is not selfish, and it does not need to be all or nothing. Attend screenings when you’re invited, speak to a doctor if something feels unusual, protect yourself where you can, and give yourself grace where you cannot. Your health is not defined by one habit, one gene, or one moment — and taking care of yourself, in whatever ways are available to you, is always worthwhile.