What does this mean?
The first encounter most often happens in childhood and goes unnoticed. After that contact the virus settles at the root of the nerve that supplies the face and stays quiet there. Long spells in the sun, an illness with a fever, a tired and sleepless period, the hormonal cycle, or a procedure during which the lip is stretched for a long time can set the virus moving again. Because the virus travels along the same nerve pathway to reach the skin, a cold sore appears at almost the same corner, or the same part of the lip, every time.
What sets a cold sore apart is its order and its place. About half a day before anything is visible, tingling, itching or tightness starts at one particular spot. Small, clear blisters then appear in a cluster on a red base; the blisters open, crust over, and the crust falls away within seven to ten days. A mouth ulcer, by contrast, has no blister stage, does not crust over, and stays on the moving lining inside the mouth. A cold sore picks out the outer edge of the lip and the skin around it. When this virus becomes active inside the mouth, it tends to affect areas bound tightly to bone, such as the palate and the gum attached to the teeth; mouth ulcers avoid exactly those areas.
In terms of passing it on, the heaviest period runs from the moment the blisters appear until the crust has dried completely. Touching the sore and then touching your eye can carry the virus there, and involvement of the eye is not something to manage at home. There is a practical consequence in dentistry: during procedures carried out while a cold sore is active, the lip is stretched, pulled back and kept wet for a long time, which can make it easier for the lesion to spread along the lip and can lengthen healing. For that reason, procedures that are not urgent are usually put off until the crust has come away. Situations that cannot wait, such as pain, swelling and injury, are dealt with using the necessary precautions.
Not every sore on the lip is a cold sore; there are conditions that look similar but are managed quite differently. The headings below bring together cold sores themselves and the conditions confused with them.
Likely causes
What helps at home?
- Note the moment you feel the tingling; the effect expected from medicines used for cold sores is more marked in that early window, and which medicine is suitable is a decision for your dentist or doctor.
- Do not touch your eye without washing your hands after touching the sore, and do not pick off the crust; the most common route of transmission is your own hand.
- While a cold sore is active, do not share towels, glasses, forks or lip balm, and do not kiss babies and young children on the lips.
- Protect your lip on days when you will be out in the sun for a long time; the sun is among the most frequently reported triggers of recurrence.
- You also have blisters, redness or discomfort in bright light on or around your eyelid.
- The blisters are moving in a band down one side of the face, from the forehead towards the tip of the nose.
- The sore has not crusted over and closed within ten days, or it is getting steadily bigger.
- Fever, widespread sores inside the mouth and being unable to take fluids come together, particularly in young children.
- You are having treatment that suppresses your immune system, or you are taking a medicine of that kind.
Frequently asked questions
- Will my dental appointment be put off if I have a cold sore?
- Procedures that are not urgent are usually put off until the crust has come away completely. The reason is that the lip is stretched and kept wet for a long time during treatment, and these conditions can make it easier for the lesion to spread. Where something cannot wait, such as pain, swelling or a broken tooth, the procedure is carried out with the necessary precautions.
- What is the difference between a cold sore and a mouth ulcer?
- A cold sore begins with tingling, makes a cluster of blisters, crusts over and usually sits on the outer edge of the lip; during the blister and crust stage it is considered contagious. A mouth ulcer has no blister stage and no crust, appears on the moving lining inside the mouth, and is not considered contagious. That is why the two are approached differently.
- It happened once, will it come back for the rest of my life?
- The virus stays at the nerve root after the first contact, but that does not mean it will recur in everyone. Some people never get another one; others get them a few times a year. How often varies from person to person, and it is usually linked to triggers such as sun, feverish illness and tiredness.
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.