The short answer
Cobalt metal, used in hard metals, batteries, and alloys, is classified as probably carcinogenic, with a suspected lung cancer link from workplace dust. Ventilation and controls reduce exposure. Dietary cobalt (vitamin B12) is not the concern.
Cobalt metal is classified as a probable human carcinogen (IARC Group 2A).
People are mainly exposed by breathing cobalt dust or fumes in certain industries.
It is most strongly linked to a suspected link to lung cancer.
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
Cobalt is a metal used in rechargeable batteries, strong alloys, and cutting tools. Breathing cobalt dust at certain jobs is linked to lung problems and, probably, lung cancer. The tiny amount of cobalt in vitamin B12 in food is not the concern here.
What cobalt metal is
Cobalt is a metal used in batteries, magnets, jet-engine alloys, and hard-metal cutting tools. IARC upgraded cobalt metal to probably carcinogenic (Group 2A) in 2023. The hazard is from inhaling cobalt dust or fumes at work, not from dietary cobalt in vitamin B12.
How people are exposed
Common ways people come into contact with it:
- Working with hard metals, cobalt alloys, or battery manufacturing
- Breathing cobalt dust or fumes, especially with tungsten carbide
- Grinding or machining cobalt-containing tools
The cancer connection
Cobalt metal is linked to lung cancer, with the clearest concern among hard-metal workers. It also causes a lung disease called hard-metal lung disease.
The International Agency for Research on Cancer (IARC), the cancer arm of the World Health Organization, places cobalt metal in Group 2A, probably carcinogenic to humans — meaning the evidence in people is limited but there is strong support from animal or mechanistic studies (evaluated in 2023). In the United States, the National Toxicology Program's Report on Carcinogens lists it as reasonably anticipated 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 cobalt metal 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
- Use ventilation and respiratory protection when working with cobalt
- Follow occupational dust and fume exposure limits
- Keep cobalt dust off skin and clothing
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
Cobalt metal is a probable human carcinogen (IARC Group 2A). 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 cobalt metal cause cancer?
Probably. Cobalt metal is classified as a probable human carcinogen: the evidence in people is limited, but animal and laboratory studies support a link. "Probable" means suspected on solid grounds, not proven.
▸How are people exposed to cobalt metal?
Most exposure happens by breathing cobalt dust or fumes in certain industries.
▸Which cancers are linked to cobalt metal?
It is most strongly linked to a suspected link to lung cancer.
▸How can I reduce my exposure to cobalt metal?
The main steps are ventilation and respiratory protection at work.
▸Does a carcinogen label mean I will get cancer?
No. A classification is about hazard — whether cobalt metal 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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