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Reflux is the backflow of anything through a sphincter, which acts like a valve in the human body. There are around 60 sphincters in the human body, six of which are part of the digestive tract but this chapter relates to reflux from the stomach to the oesophagus, or Gastro-Oesophageal Reflux (GOR/GER), which will usually carry acid into the oesophagus: the tube that delivers lumps of chewed food (known as boluses) to the stomach to dissolve in the concentrated acid it produces.
Imagine the stomach as a jam jar half full of water and food boluses as stones.
As they drop into the water, it may splash.
It can splash outside the jam jar, which is more likely if the jar is nearly full.
It doesn't matter what the stones are made of, they can still cause a splash but whether marble or sandstone, the splash is caused by the mechanical action rather than the composition.
If the jar is over-filled, it could overflow.
Again it's the quantity of the contents rather than its composition that makes a difference.
The stomach, of course, is not hard like a jam jar but soft, like a plastic bag so it can also overflow if it's squeezed.
The stomach muscles will pummel the boluses in the acid to assist in breaking them down. That activity itself could also cause the jar to overflow.
Any spillage is into the tube that carried the bolus to the stomach: the oesophagus. And the stomach isn't a container of water but very strong acid.
If we wanted to dissolve stones in our jamjar, we would put a lid on it to prevent any spillage when we shake it. The stomach has no lid as such but its entrance tube, the oesophagus, is closed by muscles pinching it tight shut, like these fingers gripping a water balloon.
A more realistic representation of the oesophagus and stomach may be modelled using a length of bicycle inner tube and a balloon.
Reflux is the backflow of stomach contents, including acid, from the balloon into the inner tube oesophagus.
Of course, being a soft bag rather than a hard container, reflux will occur if the bag is squashed.
The biggest cause of reflux is this squashing from excess belly fat.
Most people reflux because they are overweight.
As described in the chapter on Sphincters, the muscles that are involved in the Lower Oesophageal Sphincter are the diaphragm pinching the oesophagus against the phrenoesophageal ligament.
As with all muscles, they lose strength as we age, so older people are more prone to reflux as the LOS becomes incompetent.
The LOS may also be impeded by a Hiatus Hernia whereby the stomach pushes through (herniates) the hiatus hole in the diaphragm as explained here: Hiatus Hernia. It is thought that 50% of people will have a Hiatus hernia by the age of 50.
Reducing reflux.
This chapter, "Reflux Remedies" provides lifestyle modifications to reduce reflux.
Some people suggest that breathing exercises as used by opera and professional singers my help strengthen the diaphragm but, judging by the number of well known singers who have had problems with acid reflux complications, they don't appear to work very well.
If you wish to try deep breathing exercises, the NHS provides this excellent guide: Deep Breathing Exercise
Surgery.
Surgery for gastro-oesophageal reflux is not recommended unless the symptoms are seriously impeding your Quality of Life but this section, Reflux Reduction Techniques, describes those that are available, have been in the past, or hopefully will be very soon.
Page updated 8 February 2026
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