Mouth and Lips

Cracks at the corners of your mouth: why they happen, and why they keep opening again

A vitamin deficiency is only one of the possibilities; what really decides it is whether saliva is pooling in the corner

The red, cracked, sometimes crusted sore that opens at the corners of the mouth has a medical name: angular cheilitis. In Turkey it is talked about as though it had a single cause, a vitamin deficiency; yet a nutritional deficiency is found in only a quarter of the patients studied. In most cases what happens is that saliva pooling in the corner softens the tissue, and yeast and bacteria then settle there together. The answer to why saliva pools there often lies in the teeth: as the bite height drops, the upper lip hangs over the lower one and a permanent fold forms at the corner.

Short answer

A crack at the corner of the mouth forms when saliva pooling there softens the tissue and yeast and bacteria then settle in. In most cases Candida and staphylococcus are found together, which is why an antifungal cream on its own is often not enough. A deficiency of iron or a B vitamin plays a part in at most a quarter of cases; zinc deficiency is a separate nutritional risk. When the bite height drops because teeth have worn down, teeth have been lost or a denture has aged, the fold at the corner becomes permanent and the crack keeps coming back.

Its medical name: Angular cheilitis, inflammation at the corner of the mouth
The most common microbial picture: Yeast and staphylococcus found together
The share linked to nutrition: At most a quarter of cases
The overlooked reason it recurs: A dropped bite height, worn teeth or an old denture

What happens at the corner: saliva, yeast and the bite

The corner of the mouth is where the upper and lower lip meet: the skin there is thin and constantly on the move. When saliva collects and stays there, the skin softens, loses its resistance and small cracks open up. Those cracks are an open door for the yeast already living in the mouth and the bacteria living on the skin. That is why the picture is rarely driven by a single microbe; more often the two settle in together.

The numbers show this plainly. Candida yeast is found in the great majority of the cases studied, but the cases where the yeast is responsible on its own stay somewhere between a fifth and a half. In a sizeable share of cases Candida and staphylococcus are found side by side, and in some only staphylococcus or streptococcus. In practice this means an antifungal cream bought at the pharmacy works for some patients and does nothing at all for others, because the second microbe in the picture is left untreated.

Nutritional deficiencies are a real cause, but not the only one. At most a quarter of cases are linked to a deficiency of iron or a B vitamin; within the B group, B12, folic acid and B2 come up most often. Zinc deficiency is counted as a separate nutritional risk. So asking for blood tests when a crack keeps coming back is sensible, but it would be wrong to stop looking for a cause just because the tests came back normal; the cause of the remaining three quarters lies somewhere else.

The cause this page is really about is this: why saliva pools in the corner at all. The height at which the mouth closes is set by the point where the upper and lower teeth meet. As teeth wear down over the years, as back teeth are lost or as the teeth of a denture flatten, that height decreases. The jaw then closes further than it should, the lower third of the face gets shorter and the upper lip hangs over the lower one. A permanent fold forms at the corner, and saliva is held inside that fold.

This mechanism also explains why cracks are so common in denture wearers. Angular cheilitis is reported around three times more often in denture wearers than in the general population, and in some series it is reported in more than a quarter of them. The cause is not the denture itself but a denture whose height was never set correctly, or has worn down over the years. A denture is worn for years on end; as its teeth flatten, the bite quietly drops with them.

A dropped bite also clears the way for the yeast inside the mouth. In denture wearers, the fungal picture seen on the palate and the crack at the corner of the mouth are often found together; the sore at the corner is frequently the outward overflow of a source inside the mouth. Putting cream on the corner and never looking inside the mouth is one of the commonest reasons it keeps coming back.

Alongside these there are other factors that make the picture easier to develop: a dry mouth, uncontrolled diabetes (the sugar in saliva feeds the yeast), a lip-licking habit, sleeping with your mouth open, excess saliva flow, smoking, treatments that suppress the immune system and medicines that dry the mouth. Most of these do not cause a crack on their own, but combined with a fold that is already there they turn the picture into a permanent one.

That is why the recurrence rate is high. Where the underlying cause is never corrected and the sore is cleared with cream alone, it comes back in most patients over the following years. So the question to ask about a crack at the corner of the mouth is not which cream is better, but what is holding saliva in that corner.

Where to look for the cause of the crack

The points below do not give a firm diagnosis; they show you which direction to look in for the cause. Closing your mouth in front of a mirror and looking at the corners is the first step in making that distinction.

When it fits

If there is a clear fold at the corner when your mouth is closedIf you can see a deep fold running downwards at the corner while your lips are closed, it means saliva is being held there. This is the most visible sign that your bite height may have dropped.
If your back teeth are missing or noticeably worn downWhen the back teeth that carry the load of chewing are lost or flattened, the mouth closes further. A crack that keeps coming back and a gap at the back of the mouth are usually two parts of the same story.
If the teeth of your denture have flattened, or the denture is oldIf you have been wearing the same denture for years, the bite height may have dropped as its teeth wore down. This is a separate matter from how well the denture sits; a denture can feel tight and still be too low.
If there is redness or a white coating inside your mouth as wellIf the palate is broadly red or there is a white coating on the tongue that wipes off, the crack at the corner may be the outward face of a picture inside the mouth. In that case the two have to be treated together.

When it doesn't

If the crack is one-sided, hard-edged and growingAngular cheilitis is usually on both sides and responds to treatment. A sore settled on one side only, hardening or growing, does not fit that course and needs to be examined.
If it started as blisters and then crusted overA sore that begins with blisters on the outer edge of the lip and then crusts over suggests a different picture. Your dentist should make the distinction; do not try creams on your own.
If there is no improvement within two weeks of treatmentThe check-up after two weeks of treatment is a step set aside for reassessing the picture. If there is no response, either the second microbe has been left untreated or there is another cause underneath.
If it comes with tiredness, pallor or breathlessnessThese symptoms can go along with anaemia. Rather than dealing with the crack on its own, it is right to ask your doctor for tests for iron and the B vitamins.

What is looked at when you see a dentist

With a crack that keeps coming back, the aim is not to close the sore but to find what is holding saliva in the corner. The order is usually this.

1
Examining the corner and the inside of the mouth together
Looking only at the corner is not enough. The palate, the tongue, the inside of the cheeks and, if you wear a denture, the tissue underneath it are all examined; if there is a source inside the mouth, the sore at the corner may be feeding off it.
2
Assessing the bite height
With the mouth closed, the proportion of the lower third of the face, the position of the lips relative to each other and the depth of the fold at the corner are assessed. Whether the back teeth are there, how much they have worn and, if you wear a denture, the height of that denture are all part of this assessment.
3
Asking about the triggers
You are asked about a lip-licking habit, sleeping with your mouth open, dry mouth, smoking, diabetes and the medicines you take. Taking photographs of your medicine boxes to the appointment shortens this step.
4
A referral for blood tests if needed
In recurring or stubborn cases you may be referred to your doctor for iron, B12, folic acid and zinc levels. If a deficiency is found, its treatment is planned by your doctor.
5
Planning treatment on two fronts
On one side, treating the microbial picture at the corner; on the other, correcting whatever is holding saliva there. Without the second, the first stays temporary; that is why a check-up two weeks after treatment is part of the plan.

What is done, depending on the cause

These are not chosen in order but according to the cause. Most patients need a local treatment and a correction of the cause at the same time.

Local treatment of the picture at the corner

Depending on what your dentist or your doctor prefers, you are given an ointment aimed at the yeast, at the bacteria, or at both; in widespread pictures an oral medicine may be added. Follow the patient information leaflet for how long and how often to use it, and do not stop early because the symptoms have gone.

Keeping the corner dry

A corner that stays damp does not heal. A simple barrier alongside the treatment, a moisturiser or a protective ointment, reduces the contact between saliva and skin. If there is a lip-licking habit, the sore will not close until that habit is broken.

Treating the source inside the mouth

If there is a fungal picture on the palate, the denture has to be included in the treatment: cleaning it every day, taking it out at night and soaking it in a suitable solution. Without closing off the source inside the mouth, the sore at the corner does not close for good.

Correcting a deficiency

If a deficiency of iron, the B vitamins or zinc is found, its treatment is planned by your doctor. Starting a supplement on your own without being tested both hides the cause and can lead to the wrong supplement.

Rebuilding the bite height

If the cause is a dropped bite, the answer is not at the corner but in the teeth. Rebuilding the height of worn teeth, replacing the missing back teeth or renewing a denture that has lost its height are what get discussed. If a single tooth needs adjusting, your own dentist plans that.

If tooth loss has spread to more than one tooth

If there are not enough teeth left to carry the bite, the height cannot be rebuilt filling by filling; a plan covering the whole mouth is then needed. This is the area we work in: in patients missing many teeth, the bite height is rebuilt from scratch while the fixed teeth are being planned. If you have a panoramic X-ray or a CBCT scan to hand, send it through the form; the dentist who will carry out the treatment reads the image and we write to you within 24 hours. This is a preliminary assessment; the final decision is made after an examination and a CBCT scan.

What using a cream alone leaves out

A crack at the corner of the mouth looks like a small problem, which is why most people stay in the same loop for years. These are the things that get left out.

The second microbe in the picture can be left untreated

In a sizeable share of cases, yeast and bacteria are present together. An antifungal cream alone, or an antibiotic ointment alone, can fall short in that picture; which one, or which combination, is needed is decided by an examination.

The source inside the mouth goes unseen

If the fungal picture under the denture is left untreated, the sore at the corner comes back shortly after it closes. Looking at the corner and not inside the mouth means leaving the cause where it is.

The loss of bite height carries on

A dropping bite height does not stop by itself. Worn teeth wear further, the load from the gap falls on the remaining teeth and the fold at the corner deepens. The crack is the most visible, but the least important, result of that process.

An underlying deficiency is missed

A recurring crack is sometimes the first visible sign of iron or B12 deficiency. Holding it down with local treatment alone means silencing that sign too.

How long it takes to clear

The course below is a general framework for a crack where treatment has started and the cause is being dealt with too.

The first few days
Burning and tightness are usually the first complaints to ease. Tearing the crack open again when you open your mouth wide is common in this period; taking smaller bites helps.
One week
Redness and crusting start to settle. If nothing has changed at all, the treatment may not match the picture; tell your dentist rather than changing the product on your own.
Two weeks
The result of local treatment is usually assessed at the end of this period. The point of the check-up appointment is as much to discuss whether the cause behind the recurrence has been corrected as to see the healing.
The following months
This is the period that really decides it. If the bite height, the state of the denture or a nutritional deficiency has not been dealt with, the sore comes back in most patients. Every recurrence is a sign that the cause is still in place.

Don't wait if

There is no improvement despite two weeks of treatment. The picture needs reassessing; the missing piece in the treatment, or an underlying cause, needs discussing.
The sore is one-sided, hard or growing. This does not fit the usual course of a crack at the corner of the mouth; it needs examining without waiting.
It clears and then comes back in the same place. With a recurring crack, what needs discussing is not the cream but the cause: the bite, the denture or nutrition.
There is redness or a white coating inside your mouth as well. The source inside the mouth has to be included in the treatment; treating the corner alone is not enough.

What determines the scope

A crack at the corner of the mouth is usually sorted out with a simple local treatment; what widens the scope is the underlying cause. These are the items that determine it:

Where the cause lies: A picture confined to the corner and a picture fed by a source inside the mouth call for different procedures.
Whether blood tests are needed: Iron, B12, folic acid and zinc tests fall under your doctor's remit, not your dentist's.
The state of the denture: There is a clear difference in scope between relining a denture that has lost its height and remaking it.
Whether the bite has to be rebuilt: Rebuilding the height of worn teeth or replacing the missing back teeth is a separate plan and a separate scope.

Frequently asked questions

Which vitamin deficiency causes cracks at the corners of the mouth?

The ones most often blamed are iron, the B vitamins (B2, B6, B12 and folic acid) and zinc. But a nutritional deficiency is found in at most a quarter of cases; in the rest the cause is saliva pooling at the corner and microbes settling in. Asking for blood tests is the right step; stopping the search because the tests come back normal is not.

Is the sore at the edge of my lip a cold sore or a crack?

A crack at the corner of the mouth sits right at the point where the lips meet, usually appears on both sides at once, and looks red, cracked and sometimes crusted. A sore that starts with blisters, crusts over afterwards and stays in one spot suggests a different picture. Your dentist should make the distinction.

Which cream helps a crack at the corner of the mouth?

There is no single right cream, because the picture can involve yeast, bacteria or both. That is why an antifungal cream works for some patients and does nothing for others. What is needed is decided by an examination; trying products one after another on your own delays healing.

Is a crack at the corner of the mouth contagious?

The yeast behind the picture is already present in most people's mouths, so no infection from outside is needed for the condition to appear. What decides it is saliva pooling at the corner and the skin losing its resistance. Even so, not sharing towels and lip care products is a sensible precaution.

Why is it seen more often in denture wearers?

For two reasons. First, if the height of the denture was never set correctly or its teeth have worn down over the years, the mouth closes too far, the upper lip hangs over and a fold that holds saliva forms at the corner. Second, the fungal picture under the denture can overflow to the corner. This crack is reported around three times more often in denture wearers than in the general population.

What does a dropped bite mean?

There is a height at which the mouth closes when the upper and lower teeth meet. As teeth wear down, as back teeth are lost or as the teeth of a denture flatten, that height drops. The jaw then closes further than it should, the lower third of the face gets shorter and a permanent fold forms at the corner of the mouth. Because saliva is held in that fold, the crack keeps coming back.

My crack clears up but keeps coming back. Why?

Because the treatment clears the microbe at the corner without removing what is holding saliva there. In patients whose underlying cause is never corrected, the sore largely comes back over the years. With a recurring crack the question to ask is this: why is there a fold in this corner at all?

My teeth have worn down and some of my back teeth are missing. Could that be related to the crack?

Yes, it can be directly related. When the back teeth that carry the chewing height are lost or worn down, the mouth closes further and the fold at the corner deepens. An adjustment involving a single tooth is your own dentist's job. If tooth loss has spread to more than one tooth, the bite height needs rebuilding with a plan that covers the whole mouth.

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