Helicobacter pylori (H. pylori) are bacteria that live in the stomach of about two-thirds of the global population. Strong evidence suggests that it can cause cancer.

H. pylori does not cause symptoms, and many people have it without knowing they have it. However, H. pylori can cause inflammation and ulcers in the stomach. If this occurs, a person may develop symptoms such as stomach pain, vomiting, or nausea.

H. pylori is common globally with regional variances. Left untreated, it can lead to several potential health issues, including stomach cancer.

This article explores H. pylori, its connection to stomach cancer, possible links to other cancers, and more.

What is H. pylori?

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H. pylori bacteria live in the mucous lining of the stomach. The bacteria developed various defense mechanisms against stomach acid and the immune system, which makes it difficult for the body to get rid of.

H. pylori does not cause any visible symptoms. However, it can cause chronic inflammation of the stomach lining (gastritis) and gastric ulcers. 

The presence of ulcers and inflammation can lead to symptoms such as vomiting, nausea, and abdominal pain. 

According to the Centers for Disease Control and Prevention (CDC), H. pylori is the most common chronic bacterial infection, and nearly two-thirds of people worldwide have the bacteria. It is most common in low-income countries.

The prevalence rate in the United States is about 5% in children under the age of 10. It is also more common in people with Hispanic and African American heritage.

Learn more about H. pylori.

Can H. pylori cause stomach cancer?

Both the International Agency for Research on Cancer and the World Health Organization (WHO) classified H. pylori as a type I carcinogen in 1994. A type I carcinogen means that enough scientific evidence supports a claim that the substance or thing – in this case, H. pylori – causes cancer.

The exact mechanism of how H. pylori causes stomach cancer is not fully understood, but scientists think that several factors likely contribute to its development. 

Scientists know that it can cause chronic gastritis and a reduction in stomach acid, leading to bacterial growth in the stomach. 

Learn more about chronic gastritis.

Does H. pylori increase risk of stomach cancer?

According to a 2021 review article, H. pylori can increase the risk of gastric (stomach) cancer. 

In a 2017 article, experts noted that H. pylori is the most significant risk factor for gastric cancer and accounts for nearly 90% of all stomach cancers. Stomach cancer represents 5% of all cancer diagnoses worldwide.

Learn more about bacteria and stomach cancer.

What other cancers are linked to H. pylori?

H. pylori can also increase the risk of a person developing gastric mucosa-associated lymphoid tissue (MALT) lymphoma, a rare type of non-Hodgkin lymphoma. 

Evidence connecting H. pylori to other cancers is inconclusive.

According to the National Cancer Institute, some studies showed a link between H. pylori and pancreatic cancer. However, a 2023 meta-analysis found insufficient evidence across 20 observational studies to support the claim.

Growing evidence supports the claim that it may increase the risk of colorectal cancer.

H. pylori may reduce the risk of esophageal adenocarcinoma, a type of esophageal cancer that occurs due to acid reflux and Barrett’s esophagus, which is damage to the lower esophagus from repeated exposure to stomach acid.

Learn about how H. pylori transmits between people and how contagious it is.

Other risk factors for stomach cancer

H. pylori is one of several potential risk factors for stomach cancer. Some other risk factors include:

Learn about stomach cancer.

Frequently asked questions

The following sections provide answers to some frequently asked questions about H. pylori.

How common is stomach cancer from H. pylori?

H. pylori is present in nearly 90% of all people with stomach cancer. It is the most common cause and risk factor for gastric cancer.

What is the first symptom of H. pylori?

H. pylori does not typically cause symptoms. Instead, a person may develop symptoms due to inflammation or stomach ulcers. Symptoms of these conditions may include nausea, vomiting, or stomach pain.

What happens if H. pylori is left untreated?

If left untreated, H. pylori can lead to the development of stomach ulcers and inflammation. It is a known carcinogen and can eventually cause the development of stomach cancer. 

Treatment often involves medical intervention that typically includes two antibiotics (amoxicillin and clarithromycin) and proton-pump inhibitors (PPIs).

Though not available yet, a vaccination is in development, which may help prevent the transmission of H. pylori in at-risk populations.

People planning short-term travel to areas with high incidence rates have a low risk of contracting the bacteria. More extended travel in certain areas holds a higher risk.

Summary

H. pylori is both a cause and risk factor for the development of stomach cancer. It may also increase the risk of colorectal cancer. 

It may have a protective effect against certain esophageal cancers, and no other cancers have sufficient evidence to suggest an increased risk.

H. pylori does not cause symptoms, but inflammation in the stomach and ulcer development can lead to nausea, pain, and vomiting. 

Treatment typically involves a combination of antibiotics and PPIs. In the future, a vaccine may be available to help prevent the spread of the bacteria.