Cobalt toxicity occurs due to exposure of large quantities of cobalt, a naturally occurring element found in the environment, via ingestion, inhalation, skin contact, or bloodstream contact resulting from metal wear of cobalt and chromium metal-on-metal hip implants. The only known biological function of cobalt is as a component of cyanocobalamin (vitamin B12).

Clinical presentation is variable. Continuous skin contact with cobalt may cause irritation or a rash (see allergic contact dermatitis). Acute ingestion of large amounts of cobalt is rare and not known to cause any severe manifestations; patients may commonly present with nausea and vomiting. Chronic absorption of large amounts of cobalt may lead to serious health complications. Potential clinical manifestations include fatigue, cardiomyopathy, cognitive dysfunction, hearing loss, hypothyroidism, neuropathy, polycythemia, tinnitus, and vision loss.

Individuals acutely exposed to large amounts of cobalt usually recover without any long-term complications. However, individuals who experience cobalt toxicity from long-term exposure may have irreversible health problems.