What is it?
A cold sore is a recurring infection caused by the herpes simplex virus on and around the lip. The first encounter with the virus most often happens in childhood, and in the great majority of people it passes without any signs at all. After that first encounter the virus is not cleared from the body completely; it stays in an inactive form in the ganglion of the nerve that supplies the face.
Recurrences appear when that quiet period is disturbed. The virus travels along the nerve to reach the skin and most often forms a focus at the same spot, usually where the red border of the lip meets the skin. The trouble starts before the blister does: tingling, tightness and a stinging feeling are usually noticed a few hours to a day beforehand.
A cold sore is different from the first-encounter picture in a child, which comes with a fever and widespread sores inside the mouth. That first encounter happens once and most often runs a more severe course; a cold sore, by contrast, comes back again and again, is more limited and sits on the lip rather than inside the mouth. The sore being on the edge of the lip rather than inside the mouth is the most visible sign of that difference.
Signs
You will not necessarily have all of these at once.
Why does it happen?
- 01
Sun and cold weather
Strong sunlight is among the known triggers; recurrences appearing after time at the seaside or in the snow are often described. Chapping of the lip in cold, windy weather can bring about the same result.
- 02
Feverish illnesses, tiredness and stress
Flu-like infections, feverish spells, lack of sleep and heavy stress can set off a recurrence. The everyday link people make between cold sores and fever comes from this relationship.
- 03
Stretching of the lip and dental procedures
During long dental treatments, stretching of the lip, injections and mechanical strain in the area can lead to a cold sore in the days after the procedure in people who are prone to them. This does not mean that the procedure was done wrongly.
- 04
Times when the immune system is suppressed
With some medicines, during long-standing illnesses and during treatments that suppress the immune system, recurrences can become more frequent and the lesions can be wider and last longer. In this group, management is planned together with the doctor concerned.
How does it progress?
- 1
The warning stage
Before any blister appears, tingling, itching, tightness and stinging are felt on the lip. It lasts a few hours to a day. If a medicine is going to be used, this is the stage at which most benefit has been reported.
- 2
The blister stage
Small blisters filled with clear fluid appear in a cluster on a red base. This is the stage at which the viral load is highest and infectiousness is accepted to be greatest.
- 3
Bursting and crusting
The blisters burst, leaving a moist area on the surface, and then crust over. The crust can split and bleed; picking at it makes healing take longer.
- 4
Healing
The crust drops off and the redness underneath fades over the following days. In most people the whole process takes seven to ten days and usually leaves no mark.
How is it treated?
In most people a cold sore heals as it runs its own course; the aim of treatment is to shorten it and to ease the symptoms. Antiviral medicines, whether as a cream or taken by mouth, have been reported to give more benefit when they are started during the tingling stage. Whether these medicines are needed, in what form and for how long they are used, is decided by a clinician; where recurrences are frequent and severe, the assessment is shared with dermatology or infectious diseases.
The clinic's direct concern in this picture is managing appointments. During an active episode, dental treatment that is not urgent is usually put off. There are two reasons for this: stretching the lip can make the lesion larger and delay healing; and because the fluid in the blisters is infectious, there is a risk of spread during the procedure. If you have a cold sore on the day of your appointment, telling us beforehand lets the plan be made accordingly.
Preventing spread matters as much as treatment at this stage. During the blister and moist stages the virus can be passed on by contact; carried to the eye on the hand it can cause serious problems in the cornea, and carried to a finger it can cause an infection of its own. It is advised that you do not touch the lesion, that you wash your hands if you do, that you do not share towels or lip products, and that you avoid close contact with newborn babies and with people whose immune system is suppressed.
- If the lesions have spread around the eye, or there is redness, pain or discomfort with light in the eye
- If the cold sore has not healed for two weeks, or has spread over a much wider area than usual
- If fever, feeling generally unwell and difficulty swallowing have been added
- If you are having treatment that suppresses your immune system and recurrences have become more frequent
How is it prevented?
- Use a lip product with sun protection before going out in the sun; some recurrences may be reduced this way.
- Agree with your clinician in advance what to do when you notice the tingling.
- Do not burst the blisters and do not pull the crust off; both make healing take longer.
- During an active episode, do not share your towels, glasses or lip products with anyone.
Frequently asked questions
- Can I have dental treatment while I have a cold sore?
- For procedures that are not urgent, waiting is usually preferred. During an active episode, stretching the lip can make the lesion larger and delay healing; and because the fluid in the blisters is infectious, the risk of spread during the procedure also rises. Where something cannot wait, such as pain, swelling or an injury, the decision is made together with your dentist and extra precautions are taken.
- Is a cold sore the same as a mouth ulcer?
- No. A cold sore is caused by a virus, it is infectious, it starts with tingling and it blisters on the lip. An aphthous ulcer is not infectious, it has no blister stage, and it appears on the soft surfaces of the mouth such as the inside of the cheek, the inside of the lip and the side of the tongue. A lesion on the outer border of the lip would not be expected to be assessed as an aphthous ulcer.
- Is it possible to stop them coming back altogether?
- Because the virus stays in the body, no method has been described that removes recurrences completely. Recognising your triggers, protecting yourself from the sun and, in people who have frequent recurrences, the preventive approaches a clinician plans, may reduce how often they happen. If you are having many recurrences in a year, it is worth having this assessed separately by a doctor.
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.