A sore on the lip that won't heal: when should you worry?

What we call a sore on the lip can be several different conditions, and each has its own timetable. Knowing the timetable is the easiest way to tell which one can wait and which one needs an examination. The NHS writes that cold sores usually clear up on their own within 10 days, while mouth ulcers heal within a week or two. A sore in the same place that goes far beyond these times no longer belongs in the ordinary category.

A cold sore (herpes) comes in a familiar order. According to the NHS, a tingling, itching or burning feeling starts first, one or more painful blisters appear over the next 48 hours, and the blisters burst and crust over. A cold sore is contagious from the first tingle until it has completely healed. If it appears in the same place in this order every time and heals in 10 days, it is most likely a cold sore. But the NHS asks you to see a doctor if a cold sore has not started to heal within 10 days, is very large or very painful, or if you have a condition that weakens the immune system, such as chemotherapy or diabetes.

Sores inside the mouth and on the inner surface of the lip can often be traced to a cause. The NHS lists the commonest causes of a single ulcer as biting the inside of the cheek, dental work that does not fit well, burns from hot food and brushing too hard. If the sharp edge of a broken tooth or the edge of a denture keeps rubbing on the same spot, the sore will not heal for as long as that rubbing continues. With a sore like this, the first thing to do is have the edge smoothed and watch whether the sore heals within two weeks.

The condition that really needs attention is actinic cheilitis: the damage that years of sunlight leave on the lip, especially the lower lip. DermNet writes that it mostly affects fair-skinned adults who live in sunny regions and work outdoors, that it is three times as common in men as in women, and that in 90% of cases it sits on the lower lip. In a review that pooled 728 patients from 13 studies, the commonest findings were dryness (99%), blurring of the line between the red part of the lip and the skin (82%), scaling (69%) and thinning of the tissue (69%).

You can look for these signs yourself in the mirror. In good light, compare your lower lip with your upper lip. On a healthy lip there is a sharp border between the red part and the skin, as if it had been drawn; with actinic cheilitis this border becomes blurred and the red part seems to merge into the skin. A lower lip that is dry and flaky, with white thickened patches or reddened areas here and there, and that does not improve even when you apply lip balm, fits this picture. This is not a diagnosis; but if a sore that opens and closes comes on top of this appearance, that is reason enough not to put off an examination.

Actinic cheilitis is regarded as a precancerous condition, meaning it can turn into lip cancer (squamous cell carcinoma) over time. In the patients examined in the same review, the rate of transformation into cancer was 14%. This figure needs to be read with care: the studies in the review were made up of patients examined by biopsy, and the rate should not be read as the risk for everyone in the population who has actinic cheilitis. The real practical finding is this: in the same review, crusting, ulceration and reddened areas were associated with lip cancer, while scaling was associated with actinic cheilitis. DermNet, too, writes that cancer should be suspected when a spot on the lip becomes tender, a sore does not heal or a growing lump develops.

The biggest risk factor for lip cancer is the sun. The national register of 2,111 patients diagnosed with lip cancer in Sweden between 2008 and 2022 shows this, and the course of the disease, well: the median age at diagnosis was 76, 57% of patients were men, and 82.6% of tumours were on the lower lip. 81.7% of tumours had been caught at the earliest stage (T1), spread to the lymph nodes in the neck was present in only 2.7% of patients, and five-year survival was 70.5%; when the patients' advanced age is taken into account and they are compared with the general population of the same age, this figure rises to 90.8%. In other words, lip cancer is mostly caught early, and when it is caught early the outcome is good; the price of being late is paid by an advanced stage.

Smoking and alcohol play a large part in the overall risk picture for mouth cancer. Cancer Research UK estimates that around 17% of mouth cancers in the UK are linked to smoking and around 35% to alcohol; it also notes that the risk is higher in people taking immunosuppressant medicines after an organ transplant. If you work outdoors, smoke, have had a transplant or have fair skin, your threshold for a lip sore that will not heal should be lower.

The conditions in the first list heal within their own time. If a single item from the second list applies to you, stop watching the sore and book an appointment.

Your first port of call may be your dentist or your GP; because the lip is part of both the mouth and the skin, dermatology and oral and maxillofacial surgery also do this work. The sequence below shows the general course.

1. 1

   You are asked about the history of the sore

   When did the sore start, has it ever closed completely, did it come with tingling like a cold sore, was there a bite or a burn. If you have dated photos, show them; this is the easiest way for the doctor to see whether it has been healing.

2. 2

   Risk factors are discussed

   Working outdoors, sun exposure over the years, smoking, alcohol, an organ transplant or immunosuppressant medicines are asked about one by one. These answers set the threshold for a biopsy.

3. 3

   The lip and mouth are examined

   The sharpness of the lip border, scaling, white or reddened areas, the edge of the sore and any hardness beneath it are assessed by touch. The inside of the mouth, the tongue and the lymph nodes in the neck are checked in the same examination.

4. 4

   Any source of rubbing is removed

   If a sharp tooth edge or denture edge is rubbing on the sore, this is corrected first and the sore is watched for a short time. If it does not heal even though the cause has gone, the next step follows.

5. 5

   If there is any doubt, a tissue sample is taken

   DermNet writes that actinic cheilitis is usually recognised by its appearance, and that a biopsy is done when cancer or an inflammatory cause is suspected. A small piece is taken under local anaesthetic and sent to pathology; your doctor explains the result to you.

6. 6

   A treatment and follow-up plan based on the result

   For actinic cheilitis, one of the options of cream, laser or surgery; for cancer, treatment that is mainly surgical; for a cold sore or an injury, watching. In every case, protection from the sun is part of the plan.

There is no single treatment for a lip sore; the biopsy result and the cause of the sore decide the route.

The following are the decisions that most often waste time with this complaint.

The times below are thresholds based on the sources. If the course of your sore does not match them, it is time to stop watching it.

1. The first 48 hours

   With a cold sore, the blisters appear within this time after the tingling. An injury sore, on the other hand, is obvious straight after the event.

2. 10 days

   The NHS writes that cold sores usually clear up within this time. See a doctor about a cold sore that has not started to heal in 10 days.

3. 1–2 weeks

   According to the NHS, ordinary mouth ulcers heal on their own within this time. If the source of rubbing has been removed, an injury sore should also heal within this window.

4. 3 weeks

   The threshold the NHS lists among the symptoms of mouth cancer. A sore that goes beyond this time should be examined, whatever the cause.

5. After treatment

   Regular check-ups are needed after treatment for actinic cheilitis or lip cancer. In the Swedish register, some recurrences were seen after three years; do not miss your check-ups.

We do not give a single figure here, because behind a sore on the lip there may be a cold sore that clears up with a cream from the pharmacy, or a condition that calls for a biopsy and surgery. These are the items that determine the scope:

The diagnosis

A cold sore, an injury, actinic cheilitis and lip cancer take entirely different routes and fall to different doctors.

Biopsy and pathology

Taking the tissue sample and examining it in pathology are separate items.

The treatment method chosen

Cream, light treatment, laser or surgery each need different equipment and time.

Removing the source of rubbing

Smoothing a sharp tooth edge or adjusting a denture is a separate item of dental treatment.