Lysine is an essential amino acid, meaning that the body cannot produce it on its own and must obtain it from food sources. It plays a crucial role in protein synthesis, hormone production, and the absorption of calcium. Foods rich in lysine include meat, fish, dairy products, beans, and legumes. In addition to its dietary importance, lysine is often used as a dietary supplement to support immune function and promote collagen production. Some studies suggest that it may help reduce the severity and frequency of cold sores caused by the herpes simplex virus. However, more research is needed to fully understand its benefits.