"Cysteine" is a supplement containing a semi-essential amino acid naturally found in high-protein foods like poultry, eggs, and dairy. It serves as a precursor to glutathione, a key antioxidant, and plays a structural role in protein formation. Cysteine contributes to immune resilience by neutralizing oxidative stress while supporting collagen synthesis for skin, hair, and connective tissue. It also aids in fat and carbohydrate metabolism. Available in various forms, including N-acetylcysteine (NAC), this supplement is commonly included in nutritional formulations.