Cold sores are caused by certain strains of the herpes simplex virus (HSV). HSV-1 usually causes cold sores. HSV-2 is usually responsible for genital herpes. However, either type can cause sores in the facial area or on the genitals. Most people who are infected with the virus that causes cold sores never develop signs and symptoms. The herpes simplex virus usually enters the body through a break in the skin around or inside the mouth. It is usually spread when a person touches a cold sore or touches infected fluid-such as from sharing eating utensils or razors, kissing an infected person, or touching that person's saliva. A parent who has a cold sore often spreads the infection to his or her child in this way. Cold sores can also be spread to other areas of the body. In Mexico during the mid-1980s, HSV-2 prevalence was 33% in 25- to 29-year-old women and 45% in those aged 40 and over in Costa Rica. In the early 1990s HSV-2 prevalence was approximately 45% among women over 60 in Mexico.The highest HSV-2 prevalence in Central or South America—60%—has been found in Colombian middle-aged women, although similar HSV-2 prevalence has been observed in younger women in Haiti (54%). HSV-2 infects about 30% of women over 30 years old in Colombia, Costa Rica, Mexico, and Panama. HSV-2 antibodies were found in more than 41% of women of childbearing age in Brazil. However, no increase in seroprevalence was associated with age in women over 40 years old in Brazil—HSV-2 prevalence was estimated at 50% among women aged 40–49, 33% among women 50–59, and 42% among women over 60. Women in Brazil are more likely to acquire an HSV-2 infection if their male partners had history of anal sex and had many sexual partners in his lifetime. In Peru, HSV-2 prevalence is also high among women in their 30s but is lower in men. Cold sores usually clear up without treatment within 7 to 10 days. Antiviral tablets or cream can be used to ease your symptoms and speed up the healing time.
Antiviral creams such as aciclovir or penciclovir (also known as Fenistil) may speed up the healing time of a recurrent cold sore infection if used correctly. Cold sore creams are widely available over the counter from pharmacies without a prescription. They are only effective if you apply them as soon as the first signs of a cold sore appear, when the herpes simplex virus is spreading and replicating. Using an antiviral cream after this initial period is unlikely to have much effect. Cold sore patches that contain a special gel called hydrocolloid are also available. They are an effective treatment for skin wounds and are placed over the cold sore to hide the sore area while it heals Various vaccine candidates have been developed, the first ones in the 1920s, but none has been successful to date. Due to the genetic similarity of both herpes simplex virus types (HSV-1 and HSV-2), the development of a prophylactic-therapeutic vaccine which is proven effective against one type of the virus would provide fundamentals for vaccine-development for the other virus type. As of 2015, several vaccine candidates are in different stages of clinical trials as they are being tested for safety and efficacy, including at least three vaccine candidates in the US and one in Australia.