Hiccups are caused by involuntary spasms of the diaphragm, causing a short, involuntary intake of breath. The intake of breath is stopped by the epiglottis (the valve that prevents food being inhaled into the airways), which suddenly closes, producing the characteristic sound.
It is not known what causes the nervous system to trigger spasms in the diaphragm, and hiccups often start without any discernible trigger. When a trigger can be determined, hiccups are often related to factors that increase the pressure on the diaphragm, such as:
- Eating too quickly
- Eating foods that are hot or spicy
- Consumption of alcohol or carbonated beverages
- Being pregnant
Prolonged episodes of hiccups that last days, weeks or even longer, may be symptomatic of an underlying disease (e.g. thyroid disease, oesophagitis, brain damage, pleurisy), or a consequence of abdominal or chest surgery.
In addition, people taking certain drugs (e.g. anti-epileptic medicines, nicotine gum) are more prone to hiccups than others.