A cold sore is a small, painful, raised area of small, fluid-filled blisters. They usually happen where the lip joins the surrounding skin. The blisters are painful and dry up to make a yellow crust which gradually heals in a few days.

Cold sores are usually found on the lips, but you can get them in other places, such as in the nostrils, the nose or around the outside of the mouth. Cold sores tend to last 5 to 7 days and can keep coming back. Most people only have them once or twice a year.

If you have a cold sore and are due to visit your dental team, check with them first. It is preferable not to treat patients with active cold sores as the affected area may be painful and may crack and bleed during dental treatment. There is also a possibility of spreading the herpes virus through the aerosols in the dental treatment, risking the health of the dental team and yourself.

Cold sores are caused by a virus (a ‘Herpes Simplex’ virus). You first get this virus in childhood or early adulthood.

Cold sores usually appear when people are ‘run down’, or ill with something else: for example, with a cold or flu. Sunlight and ultraviolet light can often bring on an attack of cold sores. Occasionally women find that they develop cold sores at particular stages of their menstrual cycle.

Yes. Cold sores are infectious, and the virus can be passed to other people by close contact (such as kissing). A cold sore is most infectious when it is blistering. It is important to try to avoid touching cold sores, because you can pass the virus on to other people’s hands and even, very rarely, to your own eyes. Avoid squeezing, pinching, or pricking the cold sore as this can spread the infection.

Yes. Antiviral creams, such as aciclovir and penciclovir, ease the pain and blistering and help the sores heal more quickly. You can buy aciclovir from a pharmacist, but penciclovir may have to be prescribed by your doctor. You need to use these creams as early as possible when the cold sore starts to develop, and you should apply your cream regularly.

The virus that causes cold sores can also cause similar diseases on other parts of the body (for example, the fingers, eyes, and genitals). It is therefore important not to touch cold sores as you may accidentally spread the virus to other parts of your body.

Once you have had the virus it stays with you and there is little you can do to avoid an attack. How often the cold sores appear varies from person to person. However, if sunlight seems to bring on your cold sores, it is sensible to put sunblock on your lips when going out into strong sunlight.

Cold sores generally clear up without treatment in about a week. However, if you have a health condition that has weakened your immune system, or if the sores don’t heal within two weeks on their own, see your doctor. If you often get attacks, your doctor may be able to prescribe an antiviral medication to treat the sores.

Don’t stop breast-feeding. However, don’t kiss your baby, especially near the mouth or eyes, while you have an active sore as this may pass the infection on to your baby.