Are Cold Sores Contagious?

Cold sores are caused by a virus, specifically, the herpes simplex virus (HSV).

Cold sores are inflamed blisters in or near the mouth and lips. Herpes simplex virus type 1 (HSV-1) causes about 80% of cold sores while herpes simplex virus type 2 (HSV-2) causes about 20%.

Cold sores are often confused with canker sores. Canker sores are not caused by herpes viruses, are not contagious, and occur mainly inside the mouth, not on the surface of the lips.

Cold sores are contagious. About 600,000 individuals per year in the U.S. develop an infection with HSV-1. By the age of 70, studies suggest about 90% of the U.S. population has been exposed to HSV-1. About 80% of HSV-1 cold sore infections result in little or no symptoms or signs.

Cold sores are spread from person to person by direct and indirect contact.

• They can be spread by:
  • kissing,
  • oral/genital contact, and
  • by indirect methods such as:
    • sharing eating utensils,
    • razors,
    • clothing, or
    • other items.

Although HSV-1 can be spread to the genitals, the spread is less frequent (about 20%) than a similar herpes virus, HSV-2 (about 80%).

Cold sores caused by HSV-1 are not considered to be a sexually transmitted disease.

There are several stages of cold sore development.

• The first stage consists of symptoms like tingling, itching, inflammation, and hypersensitivity of skin in the location where the sore or blister will later appear. In about two days, blisters begin to appear usually at the junction of the upper and lower lip. Blisters are filled with clear or yellowish fluid and may come together or merge. In some individuals, large numbers of blisters develop.
• After about two days, the blisters begin to rupture and produce grayish-reddish sores. This is a weeping stage where highly contagious fluid oozes from the sores for about one to two days. The sores then develop scabs that last for two to three days. The scabs then begin to break up and may ooze blood.
• Secondary scabs form and are usually smaller and slowly disappear, revealing pinkish skin that gradually heals. Usually, there is no scarring and the cold sores go through this whole process in about seven to 10 days, although some may persist as long as two or three weeks.
• The time from infection to the development of symptoms (incubation period) ranges from two to 12 days for cold sores.

Unfortunately, there is no cure for cold sores. However, treatment is available to reduce symptoms and signs.

• Over-the-counter treatments are available to provide symptomatic relief. Docosanol (Abreva) is an over-the-counter treatment that may decrease the time to heal the lesions.
• Prescription medications include several antivirals, such as acyclovir (Zovirax), valacyclovir (Valtrex), and famciclovir (Famvir), and are usually used for more severe symptoms and signs.

Unfortunately, cold sores can be recurrent when certain triggers (such as stress and certain medications) allow the viruses to reproduce. Cold sores usually recur in the same area, with decreasing intensity. Most cold sores are diagnosed clinically without tests. However, there are blood tests available that can distinguish HSV-1 from HSV-2.

Most normal individuals do not need to contact a physician about cold sores caused by herpes virus type 1 (HSV-1). However, if an individual (adult or child) has a weakened immune system (such as from HIV, cancer, or undergoing chemotherapy) or if symptoms are severe, frequently recurring, or persist longer than two weeks, or include eye irritation, they should contact their physician. These situations require evaluation of both the cold sores and any underlying problems that may predispose them to develop cold sores.