Metallothioneins are small, cysteine-rich proteins found in many organisms, including humans. They play a crucial role in binding and regulating essential metals like zinc and copper, as well as detoxifying harmful heavy metals such as cadmium and lead. By doing so, metallothioneins help maintain metal homeostasis and protect cells from oxidative stress. These proteins are produced in response to various stimuli, including metal exposure and oxidative damage. Their expression can be influenced by factors like diet, environmental pollutants, and disease. Understanding metallothioneins is important for research in areas such as toxicology and biochemistry.