Various conditions and occurrences can cause sores on the mouth or lips, states MedlinePlus. Accidentally biting the lip while eating, or eating food that is either too hot or too cold can cause sores. However, the herpes simplex virus also causes blisters on the lips.
Sores on the lips caused by the herpes simplex virus are called cold sores, explains MedlinePlus. These sores first begin with a tingling or itching sensation in the area. The virus then causes blisters to form before eventually crusting over. Although cold sores often appear on the lips, they can also form inside the mouth, on the gums and in the throat. Cold sores are most often associated with herpes virus type 1. However, herpes virus type 2, or genital herpes, can also cause oral sores if the virus is spread during oral sex.
Both types of herpes are spread by contact with a person who has an active herpes virus. Contact includes touching an open herpes sore or touching something that came into contact with the herpes virus. Sore are contagious even if they are not visible, according to Mayo Clinic. Nevertheless, cold sores usually heal within two to four weeks. Although the sores normally heal by themselves, antiviral medication can help reduce the healing time or minimize the severity of future outbreaks.