There is a swollen gland under my jaw: is it a lymph node or a salivary gland?

In the triangle of tissue under the jawbone, two different structures sit side by side. The first are the submandibular lymph nodes: small, bean-shaped structures that filter the lymph fluid coming from the mouth, teeth, tongue, lips and throat, and that are normally no more than a centimetre across. The second is the submandibular salivary gland: a single secretory gland that empties saliva into the floor of the mouth, through an opening under the tongue. Whichever of the two is swollen, the story changes accordingly.

A lymph node works like an alarm system. It does not fall ill itself; it enlarges when there is an infection in the area it drains. The NHS states that swollen glands mostly appear alongside common illnesses such as a cold, tonsillitis, and ear and throat infections, and that swelling caused by an infection usually settles on its own within one to two weeks. Seen from the dental side, the picture is the same: on the NHS dental abscess page, swollen glands in the neck are listed among the symptoms of an abscess. In other words, the gland under your jaw is reporting on the tooth below it.

With the salivary gland, the mechanism is completely different and has to do with blockage. When a stone made of calcium salts grows in the salivary duct, the secretion cannot get out, the pressure inside the gland rises and the gland swells. According to StatPearls, about 85% of these stones form in the gland under the jaw; around 15% form in the gland in front of the ear, and less than 5% in the gland under the tongue and the minor glands. The reason is anatomical: the duct of the submandibular gland climbs upwards, so the flow runs against gravity; the secretion of this gland is thicker and stickier; and because the secretion is more alkaline, the salts settle out more easily. When the three factors come together, this is where stones most often lodge.

Out of this comes a simple distinction you can make at home. Let us call it the meal test. Sit down to a meal, preferably starting with something sour or full of flavour, and pay attention to the area under your jaw. Swelling that comes from the salivary gland grows quickly in the first few minutes of the meal, becomes tight and painful, and goes down slowly within an hour or two of the meal ending. The NHS likewise describes how, with a complete blockage, the pain becomes more intense during the meal and lasts an hour or two. A lymph node does not run this cycle; it is unaffected by food and stays much the same all day.

The second distinction is made with your fingers. A lymph node slides under the skin when you push it with a finger, has clear borders, is the size of a bean or a grape and is usually tender; if the cause is an infection, more than one node generally enlarges together. A salivary gland, on the other hand, is felt just below the edge of the jaw as a single, spread-out fullness whose borders are not as clear as those of a lymph node. Your dentist or doctor does one further check: a bimanual examination, with one hand inside the mouth under the tongue and the other outside. If the stone is in the front part of the duct, it can often be felt this way.

The size of the stones also helps in understanding this picture. StatPearls reports that stones are mostly between 2 and 10 mm across, and that close to 8% of them are larger than 15 mm. Some small, mobile stones come away on their own; that is why the first approach is drinking plenty of water, massaging the gland gently in the direction of the duct, and increasing the flow of saliva with sugar-free gum or sour sweets. The NHS gives a clear warning here: do not use anything sharp to get the stone out, because it causes injury and infection.

And there is a picture, to be kept apart from both of these, that really is an emergency. An infection spreading from the lower back teeth can involve the spaces under the jaw and under the tongue together; this is called Ludwig's angina. According to StatPearls, 90% of cases start from the lower second and third molars, and the picture can move forward fast enough to threaten the airway. The distinguishing signs are these: swelling under the jaw on both sides that is as hard as a board, the tongue being pushed up and forward, not being able to open your mouth, drooling, a muffled voice, and difficulty swallowing and breathing. With this picture there is no time to wait.

The two lists below do not make a diagnosis; they point you to the right door. Whichever list you are closer to, if the swelling is not settling within the expected time you need to be seen.

Swelling under the jaw is not one clinician's job: if the source is a tooth, it is the dentist; if it is the salivary gland or the nodes themselves, an ear, nose and throat (ENT) specialist comes in. The sequence below shows the general flow.

1. 1

   Taking the history

   When the swelling started, whether it changes with food, whether there was toothache or a throat infection beforehand and whether there is a high temperature make the first distinction. Be sure to mention swelling that grows and goes down with meals; that is the most valuable piece of information.

2. 2

   Examination by hand

   The size of the swelling, how firm it is, whether it moves and whether it is painful are all assessed. If a salivary gland is suspected, a bimanual examination is carried out, with one hand inside the mouth under the tongue and the other outside; stones in the front part of the duct are often felt this way.

3. 3

   Checking the mouth and the teeth

   Because the source may be a tooth, the teeth on the same side are examined for decay, fractures, deep pockets and abscesses, and an X-ray is taken if needed. Inflammation around a partly erupted wisdom tooth can also cause a gland to swell in this area.

4. 4

   Imaging

   If a salivary gland stone is suspected, the first choice is usually an ultrasound scan; a CT scan is used where needed. On the lymph node side, the assessment is planned according to the findings.

5. 5

   Treatment according to the source

   If the source is a tooth, the treatment is directed at the tooth itself, and the gland settles on its own once the tooth has been treated. With a stone, plenty of fluids, massage and measures that increase the flow of saliva are tried first; for stones that do not come away, endoscopic removal through the duct or surgical options are discussed.

These are not competing with one another; depending on where the swelling comes from, one of them is the right one.

The points below are the commonest mistakes made with this complaint. The aim is to help you choose the right door and not to miss what is genuinely urgent.

The time depends on the source. The intervals below are the courses seen most often; the plan of the clinician who examines you takes priority.

1. The first few days

   With a lymph node swollen by an infection, the node is tender and can be uncomfortable when you move your neck. If the source is a tooth or the throat, the real treatment is directed there.

2. One week

   The NHS advises seeing a doctor if swollen glands have not got smaller within a week or are still growing. This can be used as the threshold for stopping watchful waiting.

3. One to two weeks

   Gland swelling caused by an infection is reported to settle on its own mostly within this time. Swelling that has not settled within it should be reassessed.

4. With a salivary gland stone

   Once the stone comes away, the swelling and the pain that comes with meals end. As long as the stone stays where it is, the swelling comes back at every meal; this cycle is not something that settles on its own.

We do not give a single figure here, because behind swelling under the jaw there may be a lymph node needing no treatment at all, a salivary gland stone needing surgery, or a tooth that has to be treated. These are the items that determine the scope:

What the source is

A gland reacting to a throat infection, a blocked salivary gland and a tooth with an abscess are completely different jobs and belong to different clinicians.

Whether imaging is needed

In some cases an examination is enough; when a stone or a dental source is suspected, an ultrasound scan, an X-ray or a CT scan comes into it.

The scope of the work on the dental side

Root canal treatment, pocket treatment, extracting a wisdom tooth and then filling the gap each carry a separate scope.

How many teeth are affected

Behind repeated infections there is usually more than one tooth. A plan built around a single tooth and a plan covering the whole mouth are not costed the same way.