Carcinoid syndrome is caused by an uncommon intestinal or lung tumor, called a carcinoid tumor, that secretes excess quantities of hormones.

Symptoms associated with carcinoid tumors (also called argentaffinomas) include attacks of severe flushing of the skin lasting from minutes to days, watery diarrhea, abdominal cramps, bronchoconstrictive attacks, and edema (swelling) of the head and neck.

Symptoms are caused by histamine, serotonin, prostaglandins, and other biologically active substances...