What Really Causes Cancer vs What People Think: Expert and WHO Insights

Cancer continues to be one of the leading causes of death worldwide. According to the World Health Organization, cancer was responsible for nearly 10 million deaths globally in 2020, making prevention and awareness more important than ever. While many people believe cancer is largely driven by genetics or bad luck, experts say the reality is far more complex and often influenced by daily lifestyle and environmental factors.

On December 17, 2025, Dr. Thomas Hemingway, MD, a board-certified physician with over 20 years of clinical experience, shared insights on cancer causation through a public Instagram post. His observations challenged common beliefs and highlighted lesser-discussed contributors that may quietly raise cancer risk over time.

Dr. Hemingway pointed out that many people associate cancer mainly with factors such as genetics, family history, ageing, sun exposure, red meat consumption, or simple bad luck. While these elements can influence risk, especially age and inherited mutations, they rarely act alone.

The World Health Organization also notes that most cancers are not caused by a single trigger. Instead, they develop due to a combination of genetic susceptibility and long-term exposure to avoidable risk factors.

The WHO estimates that 30 to 50 percent of cancers are preventable by addressing known risks. The organisation identifies several major contributors that account for a significant share of global cancer cases.

Tobacco use remains the single largest preventable cause of cancer worldwide, linked to cancers of the lung, mouth, throat, bladder, and pancreas. Alcohol consumption also increases the risk of cancers such as breast, liver, colorectal, and oesophageal cancer, even at lower intake levels.

Unhealthy diets, obesity, and physical inactivity play a major role, particularly in colorectal and breast cancers. Environmental factors, including air pollution and exposure to harmful chemicals, further add to risk. Infections such as human papillomavirus, hepatitis B and C, and Helicobacter pylori are also proven cancer causes, especially in low and middle income countries.

Drawing from his clinical experience, Dr. Hemingway highlighted additional factors that may contribute to cancer risk but often receive less public attention. These include exposure to hormone-disrupting chemicals found in plastics and pesticides, high intake of certain industrial seed oils, and heavy metal exposure.

He also pointed to hormonal imbalances such as low progesterone or reduced thyroid function, which may affect metabolism and cellular repair. Chronic stress, persistently high cortisol levels, poor sleep quality, and prolonged exposure to artificial light at night can weaken immune function and disrupt natural repair processes.

Nutrient deficiencies, emotional stress, unresolved trauma, and lack of regular sunlight were also listed as factors that may gradually reduce the body’s ability to protect itself against abnormal cell growth.

Both WHO data and Dr. Hemingway’s observations reinforce the same message. Cancer rarely develops overnight or due to one isolated cause. Instead, it often reflects the cumulative effect of lifestyle choices, environmental exposure, metabolic health, and biological stress over many years.

Reference:

1. World Health Organization. “Cancer.” Last modified February 3, 2025. World Health Organization. https://www.who.int/news-room/fact-sheets/detail/cancer

(Rh/ARC)