1. Ada
  2. Conditions
  3. Human Herpesvirus
  4. Cold Sores (Herpes Labialis)

Cold Sores (Herpes Labialis)

Written by Ada’s Medical Knowledge Team

Updated on

What are cold sores?

Cold sores, also known as herpes labialis, is a viral infection. In the majority of cases, it is caused by the so-called herpes simplex virus 1 (HSV-1) but also can be caused by the herpes simplex virus 2 (HSV-2). Patients with cold sores typically have one or more painful blisters on the lips area. [1]

Most people get infected with the herpes simplex virus 1 in childhood. The virus is usually transmitted through saliva. In the majority of cases, no symptoms occur during this initial transmission. After infection, the virus remains in the nervous system. Stress and other triggers can lead to the virus reactivating, which then leads to an outbreak of the blisters. These outbreaks can recur over a lifetime. By the age of 40, more than 90 percent of all people are infected with the virus. However, many infected people never have an outbreak.[1],[2],[3]

Although herpes on the lips is contagious and painful, it is usually a harmless infection. However, it can have serious health consequences if it affects newborns or people with impaired immune systems.[4],[5]

If you think that you might have cold sores, you can try using Ada App to find out more about your symptoms.

What causes cold sores?

The viruses that cause cold sores are very contagious. The entry port is usually the mucous membrane of the mouth, but the virus can also enter the body through a small wound. Transmission can occur if you come into direct contact with a herpes blister or the saliva of someone who currently has a herpes blister. You can also get infected if you share dishes, cutlery, towels, cosmetic tissues, toothbrushes, toothbrush holder, or razors with someone who currently has cold sores.

The people most at risk are those who have a family member or intimate partner with a cold sore outbreak. Since both herpes simplex viruses 1 and 2 can cause both cold sores and genital herpes at different frequencies, it is also possible to become infected during oral sexual intercourse if there is mucous membrane contact with an affected person.[1],[2],[3],[6]

After the virus has usually persisted for a while in the affected person’s nervous system without causing discomfort, certain factors can lead to reactivation and then to an outbreak. These factors include:[1],[2],[3],[6]

  • fever
  • menstruation
  • sunlight
  • upper respiratory tract infections
  • injuries
  • emotional stress
  • weakened immune system
  • certain medications

What are the symptoms of cold sores?

The typical symptoms of cold sores are itching and tingling, followed by painful blisters on the mouth and lip area, from which encrusted wounds eventually develop. The symptoms can last up to two weeks. During the first episode of cold sores, the blisters can be very painful and can also be accompanied by fever, muscle pain, and swelling of the lymph nodes in the face and neck.[1],[2],[3],[6]

An outbreak of cold sores typically occurs in several stages:[7],[8],[9]

Prodromal stage

  • This stage lasts about one to two days. The affected person initially only notices a tingling sensation and possible redness at the site where a blister will form. The blisters in cold sores can occur again and again in the same place. If treatment is already started at this stage, the entire duration of the outbreak can be shortened.

Blister stage

  • This stage lasts about two to three days. One or more blisters appear on and around the lips or more rarely around the nostrils. The appearance of blisters is usually accompanied by slight pain, which can be intensified by speaking, laughing, or eating.

Weeping stage

  • This is the most painful stage. It lasts about one to three days. The blisters rupture and a clear fluid emerges.

Crusting stage

  • This stage is where the bubbles crust and form scabs on the surface. This often leads to itching, and as a result, this stage is often described by those affected as the most unpleasant stage.

Healing stage

  • This stage is where the scab and crusted areas fall off. Small, temporary scars can develop until the skin has completely healed.

Good to know:

Cold sores are contagious during all of these stages. However, the greatest risk of infection is during the third stage. The outbreak of cold sores usually disappears by itself. The affected person is no longer contagious to others from the moment the skin on which the blister was located has completely healed again.

If you are not sure if this matches what you’ve been experiencing, check your symptoms with Ada.

How are cold sores diagnosed?

The diagnosis is based on the symptoms and appearance of the blisters. The examination of the fluid or a tissue sample from a blister can be used to confirm the diagnosis of the herpes virus. However, this is usually only the case if the diagnosis is unclear or if other causes are also likely. With people with a weakened immune system, the diagnostic measures may also need to be more extensive.[1],[2],[3]

What is the treatment for cold sores?

Cold sores can usually be treated quite easily, especially if the treatment is started immediately after the first signs appear. There are several factors that determine the exact type of treatment, which are:

  • Is it a pronounced initial infection or a usually milder reactivation?
  • Does severe pain or fever occur?
  • How regularly do the symptoms occur?
  • Does the affected person have a general immunodeficiency?

The treatment differs depending on these considerations. If the symptoms are rare, fairly mild, and the current outbreak is already in one of the later stages (see above), treatment may not be necessary. The available drugs counteract the spreading of the virus. For this reason, treatment with so-called antiviral medication is much more effective if it is started early, even before the virus has been able to multiply and before a blister has formed.

Medication for cold sores:

  • If the affected person is alert and notices the onset of cold sores at an early stage (when it is only tingling), a prescription-free antiviral cream, such as acyclovir cream, can be applied. This often prevents the formation of blisters and shortens the outbreak of the virus considerably. Once a blister has formed, the application of creams is less effective.

  • Alternatively, zinc-containing creams or slightly anesthetic creams can be applied. Although these creams can relieve pain, they are not as effective as antiviral creams.

  • Oral antivirals (tablets) are sometimes prescribed by doctors. However, this is the exception and usually only necessary in very severe cases. Since it is the same group of active ingredients as in antiviral creams, antiviral tablets are also much more effective if treatment is started during the prodromal phase (see above). However, if a patient has already developed blisters, doctors may prescribe oral antivirals in certain cases so that the patient can take them to prevent future outbreaks.

There is some evidence that oral antivirals may be most effective when prescribed in cases where a patient's cold sore has a known trigger, such as strong sunlight. In such cases, an antiviral tablet may be taken immediately after the person has been exposed to the trigger. This is another form of lip herpes prophylaxis and can prevent an outbreak.

There is no evidence that the combination of oral antivirals and antiviral creams reduces the duration of an outbreak more than the use of only one of the two preparations.[1],[2],[3],[6],[10]

Can cold sores be prevented?

To reduce the risk of spreading herpes simplex viruses, which can cause cold sores and genital herpes, it is important to avoid sexual contact when lesions are present. Of course, outbreaks and lesions are not always noticed by those affected. In these cases, the consistent use of condoms helps, which massively reduces the risk of infection.

  • Whenever cold sores are present, measures should be taken to avoid saliva exchange with others. This includes activities such as kissing, oral sex, and sharing food and other utensils.

  • Mothers with the herpes simplex virus can continue to breastfeed if there are no lesions on the breasts and if lesions on other body parts are completely covered. If there are active lesions on the breast, the mother should temporarily stop breastfeeding from the affected breast and should not feed pumped milk from the affected breast. Before holding the infant, care should be taken to ensure appropriate hand hygiene.

  • Antiviral medications are effective in reducing the duration and severity of outbreaks and are most effective when administered at the first sign of an outbreak. Antiviral tablets may be prescribed in certain cases so that the patient can take them as a prophylaxis against future outbreaks. [1]

What is the prognosis for cold sores?

Cold sores are a chronic viral infection in which symptom-free intervals can alternate with repeated outbreaks. The course is variable from person to person. Some people may have frequent outbreaks, while others remain completely symptom-free. 1 Although herpes on the lips is contagious and painful, it is usually a harmless infection. However, it can have serious health consequences if it affects newborns or people with impaired immune systems.[4],[5]

What are the complications for cold sores?

Cold sores generally have a low risk for complications.[1]

If you think that you might have an infection, you can try using Ada App to find out more about your symptoms.


  1. BMJ Best Practice. “Herpes simplex virus infection” Accessed June 26, 2019.

  2. Medscape. “Herpes Simplex.” Accessed June 26, 2019.

  3. AMBOSS. “Herpes simplex virus infections.” Accessed June 26, 2019.

  4. Pathology, Research and Practice. “Generalized herpes simplex virus infection in an immunocompromised patient--report of a case and review of the literature.” Accessed June 26, 2019.

  5. NHS Choices. “Neonatal herpes (herpes in a baby)”. Accessed June 26, 2019.

  6. Canadian Family Physician. “Treatment and prevention of herpes labialis”. Accessed June 26, 2019.

  7. London Doctors Clinic. “The curse of the cold sore” Accessed June 26, 2019.

  8. How to Get Rid of a Cold Sore. “Cold Sore Stages – Here’s What To Expect From Beginning To End”. Accessed June 26, 2019.

  9. American Nurse Today. “Common sense about cold sores”. Accessed June 26, 2019.

  10. University of Saskatchewan MedSask. “Cold Sore - Guidelines for Prescribing Oral Antivirals”. Accessed June 26, 2019.

This website is certified by Health On the Net Foundation.

This site adheres to the HONcode standard for trustworthy health information: verify here.