Histidine is an essential amino acid because the body cannot produce it.  Histidine is used by the body to develop and maintain healthy tissues. It coats the cells of the nervous system to ensure the transmission of messages from the brain to the rest of the body.  Adults normally produce enough histidine from other amino acids in the liver to fit their needs, but children must obtain it from the foods that they eat. It is especially needed during infancy to ensure proper growth and development. Histidine is normally found in foods such as dairy products, eggs, meat, and fish.