Risks and causes of stomach cancer

We don’t know what causes most stomach cancers. But there are some risks factors that can increase your risk of developing it. These include being older, infection, being overweight and smoking.

Anything that can increase your risk of cancer is called a risk factor. Those that lower the risk are called protective factors.

Having one or more risk factors doesn’t mean that you will definitely get stomach cancer.

Helicobacter pylori infection

Infection with Helicobacter pylori (H. pylori) causes around 40 out of 100 (around 40%) stomach cancers in the UK.  

H. pylori is a bacteria that lives in the mucous which lines the stomach. It spreads through contaminated food and water.  For most people, having an H. pylori infection will not cause any problems. But in some, H. pylori can cause inflammation and stomach ulcers. This can lead to cancer.

Other factors, such as smoking and what we eat may increase the risk of H. pylori leading to cancer. 

Blood, stool and breath tests can find Helicobacter infection. The treatment is a course of antibiotics with a medicine to reduce the amount of acid in your stomach.

Age and gender

Stomach cancer is more common in older people. Around half of stomach cancers develop in people aged 75 or over.

Men are more likely to have stomach cancer than women.

Smoking tobacco

Smoking tobacco increases your risk of getting stomach cancer.  Around 15 out of 100 (around 15%) of stomach cancers in the UK is linked to smoking. Your risk increases with the number of cigarettes smoked a day.

It is never too late to stop smoking but the sooner you stop the better.

Being overweight or obese

Being overweight or obese increases your risk of getting cancer in the top part of your stomach (the cardia). This is where your food pipe joins the stomach (the gastro-oesophageal junction). Doctors record gastro-oesophageal junction cancers as stomach (cardia) cancer. But they treat them differently to other stomach cancers. 

Around 5 out of 100 stomach cancers (more than 5%) in the UK are caused by being overweight or obese. 

Obesity means being very overweight with a body mass index (BMI) of 30 or higher. Adults who have a BMI of 25 to 29.9 are overweight.

Try to maintain a healthy weight by being active and eating a healthy diet.


Stomach cancer risk is higher in people who drink 3 or more units of alcohol each day, compared with people who don't drink or only drink occasionally.

The government recommends that people drink less than 14 units a week.

Work chemicals

Some occupations and working with particular chemicals can increase your risk of stomach cancer. For example working in the rubber production industry.

There is also some research linking exposure to asbestos and inorganic lead compounds to stomach cancer, however this evidence is limited.

Exposure to these kinds of chemicals at work is rare and there are regulations to protect people at work.

Other possible causes

You might have heard of other possible causes of cancer. Stories about potential causes are often in the media. And it isn’t always clear which ideas are supported by evidence.

We haven’t included them here, either because there is no evidence about them or it is less clear.

Reducing your risk

There are ways you can reduce your risk of cancer.

  • International Agency for Research on Cancer. List of Classifications by cancer sites with sufficient or limited evidence in humans
    Volumes 1 to 131. Accessed June 2022.

  • The fraction of cancer attributable to known risk factors in England, Wales, Scotland, Northern Ireland, and the UK overall in 2015
    K Brown and others
    British Journal of Cancer 2018. Volume 118, Issue 8, Pages 1130-1141

  • Association Between Helicobacter pylori Eradication and Gastric Cancer Incidence: A Systematic Review and Meta-analysis.
    Y Lee and others
    Gastroenterology 2016. Volume 150. Pages 1113-1124

  • Smoking status and gastric cancer risk: an updated meta-analysis of case-control studies published in the past ten years. 

    G La Torre and others 
    Tumori 2009. Volume 95. Pages 13-22

  • Body Fatness and Cancer--Viewpoint of the IARC Working Group
    B Lauby-Secretan and others
    New England Journal of Medicine, 2016. 25;375(8), 794-8

  • The information on this page is based on literature searches and specialist checking. We used many references and there are too many to list here. Please contact patientinformation@cancer.org.uk with details of the particular issue you are interested in if you need additional references for this information.

Last reviewed: 
31 Aug 2022
Next review due: 
01 Sep 2025

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