L lysine is an essential amino acid that is a necessary building block for all proteins in addition to providing sustenance and its nutritive value, l lysine is most commonly use: for the treatment and prevention of colds sores and mouth ulcers as it has been shown to inhibit normal replication of the herpes simplex virus (Hsv), shortening their normal course and duration l lysine cannot be manufactured in the body so it is therefore vital that adequate amounts be included in the diet