Histidine is an essential amino acid, so it is not produced by the body but is taken into the body with food. It is used for growth, repair of damaged tissues and production of blood cells. It is the basic building block of filaggrin, a skin protein that plays a leading role in protecting the skin barrier. It also plays a role in helping the skin retain moisture by enhancing the skin's natural moisturizing factors and ability to withstand environmental damage.