The cause of hiccups often is not known, but some of the triggers sometimes thought to cause them include the following: spicy foods, hot liquids, any disease or illness that irritates the nerves that control the diaphragm.
The hiccup reflex involves the synchronized action of the diaphragm, the muscles that open and close the windpipe (trachea), and the nerves that act upon these muscles. Within the spinal cord, the “hiccup center” seems to be located somewhere between the cervical vertebrae numbered C3 and C5. There, nerve fibers from the brain monitor the activity and signal the contraction of the nerve (phrenic nerve) that permits exhalation.
If any of the nerves in this cycle is irritated for whatever reason(s), the diaphragm may contract involuntarily (spasm) and air is drawn into the lungs. This triggers the trachea to close, generating the typical hiccup sound.
The list of conditions that may lead to intractable hiccups is very long and may require long periods of time to isolate and identify. These include but are not limited to: brain lesions, tumors, intestinal diseases, liver or kidney disorders or uremic poisoning. Chronic hiccups may be caused by surgery or the drugs used during surgery. In some cases, a cause is not identified.