Infections That Can Lead to Cancer
Infections with certain viruses, bacteria, and parasites are risk factors for several types of cancer. But most people with these infections never develop cancer.
Can infections cause cancer?
Worldwide, infections are linked to about 13% of all cancers and cause about 2.3 million new cancers per year. This percentage is higher in countries where certain infections are more common.
Since the early 1900s, scientists have known that certain infections can cause cancer in animals. More recently, research has shown that certain viruses, bacteria, and parasites are risk factors for several types of cancer in humans.
Viruses
Viruses that have been linked to cancer include:
- Human papillomavirus (HPV)
- Hepatitis B virus (HBV)
- Hepatitis C virus (HCV)
- Hepatitis D virus (HDV)
- Human immunodeficiency virus (HIV)
- Human herpesvirus 8 (HHV-8), also known as Kaposi sarcoma-associated herpesvirus (KSHV)
- Human T-lymphotropic virus-1 (HTLV-1)
- Epstein-Barr virus (EBV)
- Merkel cell polyomavirus (MCPyV)
Parasites
Parasites that can lead to cancer include:
- Opisthorchis viverrini
- Clonorchis sinensis
- Schistosoma haematobium
Bacteria
Helicobacter pylori (H pylori) is the only bacteria with strong links to cancer.
How do infections cause cancer?
How certain infections might increase the risk of cancer:
- They can damage or change cells. Some viruses directly affect the genes inside cells that control their growth. These viruses can insert their own genes into the cell, causing the cell to grow out of control.
- They can trigger chronic inflammation. Some infections can cause long-term inflammation in parts of the body. This can lead to changes in the affected cells and in nearby immune cells, which can eventually lead to cancer.
- They can weaken the immune system. Certain infections can impair the body’s immune system, which normally helps find and destroy abnormal cells before they turn into cancer.
Many of the infections that increase cancer risk can be passed from person to person, but cancer itself cannot. A person cannot catch cancer from someone else.
Although certain infections can raise a person’s risk of some types of cancer, most people with these infections never develop cancer. The risk of developing cancer is also influenced by other factors. For example, infection with Helicobacter pylori (H. pylori) bacteria can increase your risk of stomach cancer, but what you eat, whether you smoke, and other factors also affect your risk.
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The American Cancer Society medical and editorial content team
Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as editors and translators with extensive experience in medical writing.
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Last Revised: August 12, 2026
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