Hiccups, also known as hiccoughs, are caused by a spasm of the diaphragm. The diaphragm is the thin muscle between the chest and abdomen. If it suddenly and involuntarily contracts or tightens, it causes a sharp intake of breath. When this happens, you quickly close your vocal cords, which produces the ‘hiccup’ sound. Hiccups can be annoying but are not usually serious and typically go away after a while. If hiccups go on for longer than 2 days, they are considered ‘persistent’ or long-lasting, and can interfere with eating and sleeping. See your doctor if your hiccups last for more than 2 days, if you have trouble breathing or swallowing, or if you have a severe pain in the abdomen (belly).