l-Histidine is a vital protein for the formation of the brain hormone histamine. Histamine is responsible for protection of the tissues and prevention of infiltration of bacteria and toxins into the system. Insect bites, vaccines and wounds can all allow invasive substances to penetrate the body via the tissues. A complex action occurs which stimulates the immune system through the hormone thymopoeting in order to protect against invasion, when histamine is deficient the body goes into a state of toxic shock referred to as anaphylactic shock. Histamine is also responsible for orgasm and fulfilment and its deficiency can lead to impotence and sexual disfunction.