Are Cold Sores (Fever Blisters) Contagious?

  • Medical Author:
    Charles Patrick Davis, MD, PhD

    Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.

  • Medical Editor: William C. Shiel Jr., MD, FACP, FACR
    William C. Shiel Jr., MD, FACP, FACR

    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

Shocking Diseases of the Mouth

What are cold sores (fever blisters, HSV-1 HSV-2)?

Are cold sores contagious?

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.

How will I know if I have cold sores?

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 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.

How are cold sores transmitted?

Cold sores are spread 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, 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.

Quick GuideCosmetic Dentistry Before and After Photos

Cosmetic Dentistry Before and After Photos

How Long Do Cold Sores Last?

In recurrent herpes, sores start as inflamed red bumps that swell and become fluid-filled forming blisters. The blisters eventually collapse and form an ulcer. This will take two to three days.

When will I know if I am cured from cold sores?

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

When should I seek medical care for cold sores?

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, 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 to developing cold sores.

REFERENCE:

Salvaggio, Michelle R. "Herpes Simplex." Medscape.com. Nov. 14, 2014. <http://emedicine.medscape.com/article/218580-overview>.

Subscribe to MedicineNet's General Health Newsletter

By clicking Submit, I agree to the MedicineNet's Terms & Conditions & Privacy Policy and understand that I may opt out of MedicineNet's subscriptions at any time.

Reviewed on 2/13/2017
References
REFERENCE:

Salvaggio, Michelle R. "Herpes Simplex." Medscape.com. Nov. 14, 2014. <http://emedicine.medscape.com/article/218580-overview>.

Health Solutions From Our Sponsors