Lysine is an amino acid that is essential for protein synthesis and plays a crucial role in various physiological processes in the body. It cannot be produced by the body and must be obtained through diet or supplements. Lysine is important for the growth and maintenance of tissues, as well as the production of enzymes, hormones, and antibodies. It is also known to have antiviral properties and is often used as a supplement to support immune function and prevent outbreaks of certain viruses, such as herpes simplex.