The short answer
Aristolochic acid is a natural chemical in some plants used in herbal remedies. It causes urinary-tract cancers and kidney damage. Avoiding products that contain Aristolochia plants is the key step.
Aristolochic acid is classified as a known human carcinogen (IARC Group 1).
People are mainly exposed by taking herbal products that contain Aristolochia plants.
It is most strongly linked to cancers of the upper urinary tract.
A carcinogen classification describes hazard — whether something can cause cancer — not your personal risk at a given exposure.
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The full explanation.
The simple version
Aristolochic acid is a natural substance found in a group of plants (Aristolochia and related species) used in some traditional herbal remedies. Taking products that contain it can cause kidney damage and cancers of the urinary tract.
What aristolochic acid is
Aristolochic acid is found naturally in birthwort and related plants that have appeared in some herbal medicines and weight-loss products. Regulators warn against products containing it, but it can still appear in unregulated supplements.
How people are exposed
Common ways people come into contact with it:
- Taking herbal remedies or supplements containing Aristolochia species
- Accidental contamination of grain in some regions
- Unregulated or mislabeled botanical products
The cancer connection
Aristolochic acid causes cancers of the upper urinary tract (the lining of the kidney and ureters) and the bladder, and can cause serious kidney damage.
The International Agency for Research on Cancer (IARC), the cancer arm of the World Health Organization, places aristolochic acid in Group 1, carcinogenic to humans — the strongest evidence category, meaning there is enough evidence that it can cause cancer in people. In the United States, the National Toxicology Program's Report on Carcinogens lists it as known to be a human carcinogen.
Hazard is not the same as risk
It helps to separate two ideas that are easy to mix up: hazard and risk. When an agency lists aristolochic acid as a carcinogen, it is making a statement about hazard — whether the substance is capable of causing cancer under some conditions. It is not, by itself, a statement about your personal risk, which depends on how much you are exposed to, for how long, and other factors. Two substances in the same group can carry very different real-world risks. The label answers "can it cause cancer?" — not "how likely is it to cause cancer for me?"
How to lower your exposure
- Avoid herbal products listing Aristolochia, birthwort, or related plants
- Buy supplements from reputable, regulated sources
- Tell your doctor about all herbal products you take
If you are looking at your overall cancer risk, small, steady steps add up. See our overview of cancer prevention and what raises cancer risk to put any single exposure in context.
The bottom line
Aristolochic acid is a known human carcinogen (IARC Group 1). The most important thing you can do is understand where exposure comes from and take reasonable steps to reduce it, without losing sleep over a single label. Focus your energy on the biggest, most controllable risks in your own life.
Words to know
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Common questions
▸Does aristolochic acid cause cancer?
Yes. Aristolochic acid is classified as a known human carcinogen, which means there is strong evidence it can cause cancer in people. How much any one person's risk rises depends on how much they are exposed to and for how long.
▸How are people exposed to aristolochic acid?
Most exposure happens by taking herbal products that contain Aristolochia plants.
▸Which cancers are linked to aristolochic acid?
It is most strongly linked to cancers of the upper urinary tract.
▸How can I reduce my exposure to aristolochic acid?
The main steps are avoiding herbal products that contain Aristolochia plants.
▸Does a carcinogen label mean I will get cancer?
No. A classification is about hazard — whether aristolochic acid can cause cancer under some conditions — not a prediction that any one exposed person will develop cancer. Your actual risk depends on the amount and length of exposure and other factors.
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