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A hiccup or hiccough (normally pronounced "HICK-up"; IPAEng: ˈhɪkʌp), is the spasmodic contraction of the diaphragm that repeats several times per minute. In humans, the abrupt rush of air into the lungs causes the epiglottis to close, creating the "hic" listen sound. In medicine, it is known as synchronous diaphragmatic flutter (SDF), or singultus, from the Latin, singult, "the act of catching one's breath while sobbing." The hiccup is an involuntary action involving a reflex arc.

The term "hiccup" is also used to describe a small and unrepeated aberration in an otherwise consistent pattern.

A bout of hiccups, in general, resolves itself without intervention, although many home remedies claim to shorten the duration, and medical treatment is occasionally necessary in cases of chronic hiccups.

Causes

Hiccups (singultus) can be caused by many central and peripheral nervous system disorders, all from injury or irritation to the phrenic and vagus nerves, as well as toxic or metabolic disorders affecting the aforementioned systems. Hiccups often occur after drinking carbonated beverages or alcohol. Persistent or intractable hiccups may be caused by any condition which irritates or damages the relevant nerves. Chemotherapy—which includes a huge amount of different drugs—has been implicated in hiccups (some data states 30 percent of patients)Fact: date=April 2009, while other studies have not proven such a relationship. Many times chemotherapy is applied to tumors sitting at places that are by themselves prone to cause hiccups, if irritated.

Phylogenetic hypothesis

Christian Straus and co-workers at the Respiratory Research Group, University of Calgary, Canada, propose that the hiccup is an evolutionary remnant of earlier amphibian respiration; amphibians such as frogs gulp air and water via a rather simple motor reflex akin to mammalian hiccuping. In support of this idea, they observe that the motor pathways that enable hiccuping form early during fetal development, before the motor pathways that enable normal lung ventilation to form; thus according to recapitulation theory the hiccup is evolutionarily antecedent to modern lung respiration. Additionally, they point out that hiccups and amphibian gulping are inhibited by elevated CO2 and can be completely stopped by the drug Baclofen (a GABAB receptor agonist), illustrating a shared physiology and evolutionary heritage. These proposals would explain why premature infants spend 2.5% of their time hiccuping, indeed they are gulping just like amphibians, as their lungs are not yet fully formed.

Treatment

Ordinary hiccups are cured easily without medical intervention; in most cases they can be stopped simply by forgetting about them. However, there are a number of anecdotal treatments for casual cases of hiccups. Some of the more common home remedies include giving the afflicted a fright or shock, drinking water (sometimes in an unorthodox manner), and altering one's breathing.