People have been pondering the precise cause of hiccups for thousands of years. Ancient Greek physician Galen, for example, hypothesized that hiccups were simply violent emotions that began in the stomach and erupted out the mouth. This hypothesis has not exactly been disproved, but since then, we have come up with many more.
We know what happens during a hiccup. During normal breathing, we take in air from the mouth and nose, and it flows through the pharynx, past the glottis and into the larynx and trachea, ending in the lungs. The diaphragm, a large muscle between the chest and abdomen, aids this airflow. It moves down when we inhale, and then up when we exhale. The phrenic nerves control the movement and sensation of the diaphragm. Any irritation to these nerves induces a spasm of the diaphragm. This spasm causes a person to take a short, quick breath that is then interrupted by the closing of the epiglottis (a flap that protects the glottis, the space between the vocal cords). The sudden closing creates the sound we all know as a hiccup.
So, hiccups are the result of diaphragm spasms. But what causes the irritation that leads to the spasm? There are only a few culprits for common hiccups, which usually disappear within a few minutes. One of the main irritants is a full stomach -- a result of swallowing too much food or air. A distended stomach pushes against the phrenic nerves of the diaphragm, increasing the possibility of irritation and, therefore, hiccups. A full stomach of spicy food can do double damage -- hot foods can be especially irritating to those nerves. As any smoker on a bender can tell you, excess smoking and drinking alcohol can also cause hiccups. A rapid temperature change outside or inside your stomach, from a cold night or a hot beverage, can be irritating enough to induce hiccups. Finally, emotions -- shock, excitement and stress -- can also trigger a hiccup fit.
Persistent and intractable hiccups can have more serious causes. There are hundreds, from hysteria to heart attacks, but most fit into one of five categories: central nervous system problems, metabolic problems, nerve irritation, anesthesia or surgery, and mental health issues. Because these causes are so varied and potentially serious, anyone suffering from hiccups for more than 48 hours should head straight to a doctor.