What causes hiccups, and what actually stops them?

A hiccup is a sudden involuntary contraction of the diaphragm, immediately followed by the glottis snapping shut about a quarter second later, and that abrupt closure produces the sound. The reflex arc involves the phrenic and vagus nerves and a center in the brainstem, and it can be triggered by eating too fast, carbonated drinks, alcohol, sudden temperature changes, excitement, or swallowing air. Why the reflex exists at all is unsettled, with one intriguing hypothesis proposing it is an evolutionary remnant of an amphibian gill-ventilation reflex, and another suggesting it helps infants clear air while nursing.

The folk remedies are not all nonsense, since most work through one of two plausible mechanisms. Holding your breath or breathing into a bag raises blood carbon dioxide, which appears to suppress the reflex. Swallowing a spoonful of sugar, gargling, drinking cold water quickly, pulling on the tongue, or the reliably odd trick of drinking from the far side of a glass all stimulate the vagus or phrenic nerve pathways and can interrupt the loop. None is reliable, and most hiccup bouts resolve on their own within minutes regardless of what you do, which is why every remedy has satisfied believers. What warrants a doctor is persistence: hiccups lasting more than 48 hours are classified as persistent and can signal an underlying condition affecting the nerves or central nervous system, and there are prescription treatments for the intractable cases, which in rare documented instances have lasted years.