How long is a cold sore contagious?

Cold sores (Herpes labialis, Fever blisters, HSV-1)

Cold sores - also known as cold sores or herpes labialis - are mostly harmless, but very unpleasant. Around 20 to 40% of all people have symptoms on a regular basis, but the infection rate in the population is 85%.

Short version:

  • Cold sores are caused by the herpes virus.
  • The infection usually occurs in childhood and adolescence.
  • Typical signs are blisters around the mouth.
  • The oozing blisters are filled with highly contagious liquid.
  • If you have been infected with the herpes virus once, cold sores can occur again and again.
  • Treatment is symptomatic with creams, gels or ointments.

The cause of the painful, itchy blisters is an infection with the herpes simplex virus (HSV), which is very common: around 85 percent of the population carry it.

Whether and how often the virus breaks out depends to a large extent on the immune system and the age of the person affected: In ten to 20 percent of those infected, primarily in adolescents and young adults, fever blisters recur at irregular intervals before they usually only occur in later adulthood rarely appear.

Pathogenmostly HSV-1 (sometimes HSV-2)
transmissionSmear infection
incubation period3 to 9 days
Symptomsoozing blisters, itching, feeling of tightness
treatmentantiviral creams, gels & ointments
Healing time7 to 10 days

How do you get infected with herpes?

The herpes simplex virus has two subgroups - types 1 and 2.

The main trigger for cold sores is HSV type 1 (HSV-1). HSV-1 is transmitted via a smear infection - e.g. when kissing or sharing dishes. The infection usually occurs in infancy or toddlerhood: Around 80 percent of all two-year-olds are already infected with HSV-1.

Herpes simplex virus type 2 (HSV-2) triggers cold sores in 20 to 30 percent of cases. Infection with HSV-2, the main cause of genital herpes, occurs through sexual intercourse and intimate contact such as petting.

It should be noted that most herpes transmissions take place when the disease is not acute. If you are infected with HSV, virus excretion occurs again and again without developing a fever blister. However, since significantly more viruses can be transmitted with an acute fever blister, this can lead to more severe initial symptoms if someone else is infected.

During an acute outbreak of cold or genital herpes, hygiene should therefore be a top priority: Cold sores can be transmitted to the genital area and vice versa all too easily. Conscientious hand disinfection can be very helpful in stopping the spread.

What are the symptoms of a herpes infection?

The incubation period for the first infection with herpes is three to nine days on average, but in rare cases it can last up to six weeks. Since the initial infection is usually inconspicuous, many people do not even know whether they are carrying the virus or not.

Possible symptoms are:

However, if fever blisters develop, this usually begins with itching and a feeling of tension, sometimes with pain. About two days later, small, weeping vesicles appear, which are filled with a highly infectious liquid, soon burst open and then form a crust. It usually takes seven to ten days for cold sores to heal.

On which parts of the body can cold sores occur?

  • Lips
  • mouth
  • Cheeks
  • Nasal entrance
  • Earlobe
  • Eyes / conjunctiva

In these cases, an ophthalmologist should be consulted immediately, as this can lead to impaired vision and, in the worst case, blindness.

  • Oral mucosa / gums

In some cases the lining of the mouth and gums can also be affected by the infection, which can lead to painful apthens and ulcers (so-called oral rot). Extensive and recurring infections can also be an indication of an immune deficiency.

When infected with HSV-1 for the first time, the vesicles can flow together to form larger ulcers on the skin and become infected with other bacteria (superinfection).

Why do fever blisters keep coming back?

HSV-1 usually enters the body through the lining of the mouth. From there it migrates along nerve fibers to the so-called trigeminal ganglion, a nerve nodule lying next to the spine - the HSV viruses linger there for life and when our immune system is weakened such as the sun, stress, lack of sleep or illness, these viruses then migrate along the nerve to the corresponding skin area and the typical signs such as tingling sensation and blistering begin.

Once you have become infected with herpes, there is still no way of getting rid of it: the virus remains in the nerve roots for life, with the readiness to become active again at any time (reactivation). So far, neither a vaccination that reliably protects against HSV nor a therapy that eliminates the virus from the body has been found.

In genital herpes, too, the HSV withdraws into the nerve roots, but into the sacral ganglia. From there, as with herpes labialis, it can be reactivated again and again and cause genital herpes.

The most common causes for the virus to migrate back from its "sleeping place" in the nerve roots and trigger fever blisters are:

How can you treat cold sores?

To date, there is no therapy that completely eliminates the virus from the body. Cold sores can therefore only be treated symptomatically. There are also local creams, gels or ointments that are regularly applied to the affected area.

In the case of frequent recurrence of cold sores and severe disease, systemic or anti-viral treatment with tablets (so-called antivirals) can also help. In the event of an outbreak, greater attention must be paid to hygiene. Direct contact with other people should be avoided because of the risk of infection.

++ More on the topic: Treatment of fever blisters ++

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Mag. (FH) Silvia Hecher, MSc, Dr. med. Sandra Tretter
Medical review:
ÖA Dr. med. Barbara Franz
Editorial editing:
Dr. med. Matthias Thalhammer, Dr. med. Lisa Demel, Tanja Unterberger, Bakk. phil. (2017), Astrid Leitner (2020)

Status of medical information:

Phytomedicins; 2008 Sep; 15 (9): 734-40. doi: 10.1016 / j.phymed.2008.04.018 (last accessed on June 9th, 2020)

Deutsche Apothekerzeitung, Finger weg vom Herpes, as of 2016, (last accessed on June 9, 2020)

Breier & Gruber: Fever blisters, herpes & Co. 1st edition, Verlagshaus der Ärzte, Vienna 2012

Mims et al .: Medical microbiology / infectious diseases. Elsevier, Munich 2006

Suerbaum et al .: Medical microbiology and infectious diseases. 7th edition, Springer Verlag Berlin Heidelberg, 2012

E. Mayatepek: Pediatrics. Elsevier Publishing House.
Clinical Evidence

De Carvalho RR: Effect of laser phototherapy on recurring herpes labialis prevention: an in vivo study. Lasers Med Sci. 2010 May; 25 (3): 397-402. Epub 2009 Aug 11

More articles on the topic

Genital herpes

Genital herpes is a contagious viral disease that is mainly transmitted through unprotected sex.

Herpes simplex

An infection with type 1 herpes viruses occurs in most cases in childhood.

ICD-10: B00.1