The diaphragm muscle that separates the chest from the abdomen contracts and relaxes to move air in and out of the lungs. Hiccups or hiccoughs occur when the diaphragm spasms rhythmically. With each contraction of the diaphragm, the vocal cords suddenly close, causing the "hiccup" sound. Hiccups usually have a benign cause, but prolonged hiccups lasting more than 48 hours can indicate a serious underlying medical condition. The Mayo Clinic says that about 1 in 100,000 people suffer from intractable hiccups that last for more than a month.
Short-term hiccups, lasting for less than 48 hours, typically occur when the stomach distends after a large meal or from drinking a lot of fluid. Carbonated and alcoholic drinks are especially likely to distend the stomach and bring on a bout of hiccups. Stomach distension impinges on the diaphragm and can disrupt its function.
Sudden temperature changes, such as stepping outside on a very cold day, or eating or drinking very hot or very cold items, can bring on hiccups. The mechanism linking temperature change to spasms of the diaphragm is not clear.
Over-excitement, anxiety and stress can cause short-term hiccups. Again, the mechanism is not clear, but these states often change breathing patterns, providing a link to diaphragmatic function.
Two important nerves, the vagus nerve and the phrenic nerve, regulate the contraction of the diaphragm. Irritation of these nerves can bring on long-term hiccups lasting for more than 48 hours. Common culprits include a hair or something else touching the eardrum, sore throat, a tumor in the neck or a goiter, or acid reflux, according to the Mayo Clinic. The common home remedy of swallowing a teaspoon or so of sugar might work because it irritates the pharynx, stimulating the vagus nerve, according to the Merck Manual. Another common home remedy--holding the breath or breathing deeply--can cure hiccups by consciously over-riding the involuntary nerve input to the diaphragm, re-setting it to a normal pattern.
Surgery can precipitate hiccups. After abdominal surgery, the stomach can distend, triggering an episode of hiccups. Other factors, such as general anesthesia and intubation, which irritates the throat, can also contribute to hiccups.
A variety of metabolic conditions, including diabetes, kidney failure and electrolyte imbalance can bring on long-term hiccups. Drugs used to treat such disorders as barbiturates, steroids and tranquilizers can also cause hiccups. Brain disorders, including a tumor, encephalitis, stroke or a brain injury, can disrupt nerve signals to the diaphragm, causing long-term hiccups.