The Friday Question: Why Do We Hiccup?

This week’s Friday question was asked by the very lovely Zan, and it was about the science of hiccups. Why do we get them? What are they for? And how can you make them stop?

The science of hiccups is a funny thing, we know what a hiccup is, and we know some of the things that cause them, but we don’t really know what good they do. I should note that this post is about common hiccups, which most people get and which pass within an hour. There are also more serious, and longer lasting, types of hiccups that can be caused by nerve damage, drugs or illness.

A hiccup is a sudden short intake of breath; normally when you breathe air goes into your mouth or nose, and heads to your lungs via a scenic tour of your trachea. On its way to the lungs air passes through the pharynx, the space behind your mouth and nose, and heads past the epiglottis, which is the crucial little bit of you responsible for keeping your airways and your oesophagus separate, and protecting your vocal cords. Below the epiglottis is the larynx, home of the vocal cords. Air whizzes through here and heads on down the trachea to the lungs. It’s all very leisurely and straightforward, a pleasant walk in the park.

A hiccup is a disturbance in this lovely easy breathing pattern. Your diaphragm, which lives underneath the lungs, like a troll under a bridge, usually helps the process of breathing by lifting up when we breathe out and moving down when we breathe in. The diaphragm is a weightlifting troll, although to be fair it is only lifting air, which isn’t that impressive. I can totally lift air. Anyway, the movement of the diaphragm is controlled by the phrenic nerves. If anything irritates these nerves, they send a message to the diaphragm that causes it to spasm, snapping suddenly downwards and leading to a short sharp intake of breath. In response to this unexpected sudden breath, the epiglottis speedily shuts; this is the ‘hic’ sound we all know and love.

This is all very well: hiccups are caused by our phrenic nerves getting irritated and forcing the diaphragm troll under our lungs to suddenly squat down low, but what exactly is irritating our phrenic nerve in the first place? Actually, our phrenic nerves are clearly very moody, irritable little things, because quite a lot of things can annoy them into causing hiccups. One of the most common is eating too much, or swallowing too much air; when your stomach is very full, all stretched out and rounded, it can push up against the phrenic nerve, which irritates it. Other things that irritate the phrenic nerve include very spicy food, drinking alcohol, drinking something very cold or very hot, and sometimes emotions like stress or shock. Basically, the phrenic nerve is the Grumpy Old Woman of the nervous system.

These are some reasons that we get hiccups, but none of them makes sense as the actual purpose of hiccups in general. In fact, nobody really understands the purpose of hiccups. There are some theories; one is that they’re an evolutionary hangover from a time when we had gills. Creatures with gills need to close their epiglottis to stop water going into their stomach while they force it across their gills, and the process involved in this is similar to the process of a hiccup. This theory also suggests a reason that hiccups have hung around this long; it might be a mechanism to help young mammals learn to suckle, without accidentally inhaling milk into their lungs. Another theory, on the other hand, suggests that a hiccup is a complex process developed to remove air from the stomachs of young mammals.

Neither of these theories is necessarily correct, and there are other theories out there too, I just found those two particularly interesting!

Regardless of why we hiccup, hiccupping can be annoying, so despite the fact that they will usually pass of their own accord fairly quickly, we always try to stop them. I think everyone was told a different way to stop hiccupping while they were growing up, from eating a spoonful of sugar, to holding their nose, to making someone jump, or drinking water upside down. Zan told me she has to drink water WHILE holding her nose.  I always take a huge deep breath, a mouthful of water and swallow in 12 tiny sips. The actual key to controlling, and hopefully stopping hiccups, is really to control your breathing and your diaphragm. Most hiccup home remedies that actually work will involve some way of regaining control of your breathing muscles; for example both mine and Zan’s methods involve holding our breath, which squashes the diaphragm flat and hold it there, so that it can’t spasm.  Whatever your method, if it works for you, then go with it, there’s no scientifically proven single cure for hiccups anyway. Although it is a nice excuse for a spoonful of sugar.


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