Cold sores, caused by the herpes simplex virus, are small blisters that form on the lips or around the mouth. These sores usually go away without treatment within 7 to 10 days, but can last up to 2 weeks. Hot sun, cold wind, a cold or other illness, or a weak immune system can trigger an outbreak of the herpes simplex virus. The first time you have a cold sore, symptoms may not start until 20 days after you were first exposed to the virus.
The sores can last several days and the blisters can take two to three weeks to fully heal. Recurrences usually appear in the same place each time and tend to be less severe than in the first outbreak. If you are pregnant, you can continue to use antiviral medications if there is serious concern that the herpes virus could be transmitted to the baby. Oral herpes is most often spread through non-sexual contact with infected saliva, such as kissing, touching the infected person's skin, or sharing infected objects, such as lip balm, cutlery, or razors.
Sometimes, oral and genital herpes viruses can spread even when there are no sores or blisters in the mouth. Once you've had an episode of herpes infection, the virus remains latent in nerve cells in the skin and can appear as another cold sore in the same place as before. The herpes simplex virus can be difficult to diagnose because it can be confused with many other infections, such as allergic reactions. While HSV-1 is the most common cause of cold sores, HSV-2, which causes genital herpes, can also cause cold sores.