Your oral & dental health A-Z oral health information Cold sores What is a cold sore? 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, on 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. How do I get cold sores? Cold sores are caused by a virus (a 'Herpes Simplex' virus). You first get this virus in childhood or early adulthood, and it may cause a fever and mouth ulcers (called 'primary herpetic gingivostomatitis'). About a third of people who get this 'primary' infection go on to develop cold sores in later life. However, many people with cold sores did not get this primary infection. What brings on the cold sores? 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. Are they infectious? 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. Can they be treated? 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. How can I avoid getting one? 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. If I have a cold sore should I see my doctor? 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. I have a cold sore but am due to see my dentist. Will they still be able to treat me? If you have a cold sore and are due to visit your dental team, check with them first. Some dentists prefer not to treat patients with active cold sores as the affected area may be painful, and may crack and bleed during dental treatment. What if I'm breast-feeding? 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. Can you only get cold sores around the mouth or can you get them on other parts of the body? 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. People who viewed this page also visited... Gum disease Tooth decay Dry mouth Need more advice? If you need free and impartial advice about your oral health, contact our Dental Helpline by email or call 01788 539780 (local rate call in the UK). Our Dental Helpline is completely confidential and has helped almost 400,000 people since opening over 20 years ago. Contact our experts by telephone, email or online enquiry, Monday to Friday, 09:00 - 17:00.