Your risk of developing stomach cancer depends on many things including your age and lifestyle.
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.
H. pylori is a bacteria that live in the mucous of the lining of the stomach. For most people, having a H. pylori infection will not cause any problems. But in some cases long term infection can cause inflammation and stomach ulcers.
There is also some evidence that diet may interact with H pylori to increase the risk of stomach 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 get the disease compared to women.
Smoking tobacco increases your risk of getting stomach cancer. Around 1 in 5 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.
More than 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.
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.
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.
Reducing your risk and 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.