What does this mean?
The corner of the mouth is a fold where skin meets the lining of the mouth, and it moves constantly as you speak and eat. If that fold deepens, the saliva that runs into it cannot dry. Skin that stays wet softens and cracks; the yeasts and bacteria already present in the mouth settle in through the crack. Because the damp groove suits them, the corner simply will not close. That is why opening your mouth wide burns, why there is a little bleeding in the mornings, and why it crusts over.
What separates this from dry lips is where it is and which way it runs. Ordinary chapped lips affect the whole surface of the lip, look dry and flaky, get worse in cold and wind, and improve noticeably with a moisturiser. The problem described here is only at the two corners, often on both sides at once, and it is wet rather than dry, so a moisturiser most often does not help; the cause is not dryness but, on the contrary, constant damp. A cold sore can sit at the corner too, but a cold sore begins with tingling, makes a cluster of blisters, and crusts over and closes within ten days; a cracked corner lasts for weeks and reopens with movements such as eating and yawning.
The height of the lower part of the face may decide whether the crack carries on. When back teeth are lost, or when a denture has worn down or was made lower than it should have been, the chin comes closer to the nose, the fold at the corner deepens and saliva settles there permanently. That is why reviewing the height of your bite and the fit of your denture is directly relevant to this complaint. Low iron, B12 and folate, high blood sugar, dribbling during sleep, a lip-licking habit and mouth breathing are also counted among the things that keep the picture going. In children and teenagers the most common cause is lip licking.
Behind a crack at the corner of the mouth there is most often not one cause but several factors laid on top of each other. The headings below gather those factors and the conditions that look similar.
Likely causes
What helps at home?
- Try to give up the habit of wetting the corners of your mouth with your tongue; the wetness is the cause of this crack, not the cure for it.
- If you wear a denture, take it out every night, clean it with a brush and water and keep it somewhere it can stay dry; the layer that builds up on a denture can be a source for the sore at the corner.
- Do not apply leftover antifungal cream, steroid ointment or antibiotic ointment from family or friends at random; as what is growing at the corner changes, so does the right approach.
- If you also have fatigue, paleness, a burning tongue or frequent mouth ulcers at the same time, say so at your appointment; this complaint may not be assessed on its own.
- The crack has not healed in two weeks, or it is getting steadily deeper.
- The sore is spreading from the corner of the mouth onto the skin of the cheek, or its edges are hardening.
- Redness, swelling and pain are increasing, or you have developed a fever.
- A dry mouth has been joined by dry eyes over the same period.
- There is a separate sore on the lip itself, away from the corner, that will not heal and that crusts over and opens again.
Frequently asked questions
- Do I have a vitamin deficiency, should I have tests?
- Low iron, B12 and folate are among the things looked into with this picture, particularly if the crack is on both sides and keeps coming back. Which tests to request, and how the results should be read, is a decision for your dentist or doctor. Starting supplements on your own can blur the result and mask the real cause.
- Why does lip balm not help?
- Because the problem is not dryness but the corner staying constantly wet. A moisturiser can sometimes hold that wetness in the corner and so keep the problem going. A barrier ointment that keeps moisture out may help, but without addressing why the fold has deepened and what is growing there, a lasting improvement is not usually expected.
- Could my denture have something to do with it?
- It could. A denture wears down over time, or it may have been made lower than it should have been to begin with; the jaw then closes too far towards the nose and the fold at the corner of the mouth deepens. The layer that builds up on the denture can also be a constant source for the corner. These two points are assessed together at the examination.
This content is for general information and does not replace an in-person examination. Symptoms overlap between conditions, and a diagnosis can only be made clinically.