Saliva constantly flows from the salivary glands in your mouth. Sometimes, the chemicals in saliva can crystalise to form a tiny stone.
Salivary gland stones ('salivary calculi') can become lodged in the duct (tube) leading from the salivary gland, blocking the flow of saliva into the mouth. This can cause swelling and pain in the gland.
The stones are largely made of calcium, and most are smaller than 1cm in diameter, although they can range from being less than 1mm to as large as a few centimetres.
Usually, a procedure is needed to have the stone removed, although it can sometimes come out of the mouth on its own, or after a bit of probing.
You could try dislodging the stone yourself by sucking on lemon to stimulate saliva flow.
Why do salivary stones form?
It's not known why salivary gland stones form. There's usually no imbalance of calcium anywhere else in the body.
The formation of a stone may be linked to changes in the flow of saliva through the gland. You're probably more at risk of one if saliva is reduced or thickened – for example, if you're dehydrated, or not eating much (eating stimulates greater flow of saliva).
Certain medicines may also increase your risk of salivary stones.
Where do they form?
Most salivary gland stones form in one of the submandibular glands – you have two of these glands (one on each side) under the bottom of your mouth.
The stone becomes lodged in the duct running from the submandibular gland underneath the tongue.
Saliva is also produced in the parotid glands just below and in front of your ears, and in the sublingual glands beneath your tongue, but it's much less common for stones to form here.
How do I know I have a salivary gland stone?
If the stone is very small and not blocking the duct, you may not realise you have it as there may not be any symptoms.
A larger stone may be visible when you open your mouth wide. If the stone is big enough to cause symptoms, these symptoms will usually continue until the stone falls out or is removed.
Dull pain and swelling
If the stone partially blocks the duct and stops some of the flow of saliva, you might have:
dull pain over the affected gland that comes and goes
swelling of the gland, which may flare up and down over time
infection of the gland – it will be very painful and an abscess may form, which can make you feel unwell
Intense pain and swelling after eating
If the salivary gland is completely blocked, you may feel sudden, intense pain after you start eating at mealtimes.
This is usually followed by swelling, which eases during the hours after a meal.
Swelling and pain happens because the saliva cannot exit the blocked duct, so it backs up and builds up in the gland.
How is it diagnosed?
A GP may be able to see the stone when they examine your mouth. Otherwise, an X-ray would usually show it up.
If the stone doesn't show up on X-ray, you may need one of the following more detailed scans:
A computerised tomography (CT) scan, which uses X-rays and a computer to create detailed images of the inside of the head and neck area.
A magnetic resonance imaging (MRI) scan, which uses strong magnetic fields and radio waves to produce detailed images.
Sialography – where a dye is injected into the gland before an X-ray is taken.
Sialendoscopy – where a thin tube with a tiny light and camera on its end (an endoscope) is inserted into the duct, so the doctor can see into the gland. If a stone is visible, this can be removed at the same time (see below).
How is it removed?
Your GP may attempt to free up the stone by probing your salivary duct with a thin, blunt instrument.
If this doesn't work, you may need a procedure called a therapeutic sialendoscopy (mentioned above). A local anaesthetic is given to numb the mouth, and a very thin endoscope is pushed into the duct. If a stone is seen, a tiny instrument at the end of the tube is used to grab the stone and pull it out.
If the stone is large, it may need to be broken up first, using shock wave treatment (where ultrasound waves are directed at the stone to break it up). This is called extracorporeal shock wave lithotripsy.
In the past, doctors would remove salivary stones by making a small incision in the mouth, but such an operation is rarely necessary nowadays.
What happens after it has been removed?
Salivary stones are usually a one-off event and most people who develop one won't develop another again.
If you're unlucky enough to develop another one, or develop a few at the same time, you may need an operation to remove the whole salivary gland. Your doctor will explain this procedure to you in detail. You'll still be able to produce enough saliva from the other glands.