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Cold sores: Learn More – Can cold sore outbreaks be prevented?

Last Update: March 23, 2022; Next update: 2025.

Sunscreen and good lip care can protect your lips from potential cold sore triggers like sunlight and cracked lips. There is a lack of good research on whether medication for the prevention of cold sores helps in people with a healthy immune system.

Some people keep getting cold sores. It is estimated that 5 to 10 out of 100 people who have cold sores get them more than five times a year. Avoiding potential triggers may help to prevent them.

If someone often has cold sores that really affect them in everyday life, preventive treatment with antiviral tablets may be considered. But these tablets have only been approved for the prevention of other types of herpes infections. If they are used for the treatment of cold sores, it is considered to be non-approved (“off-label”) use, for which special regulations apply.

What can increase the likelihood of cold sore outbreaks?

Cold sores are caused by viruses in nerve cells in the lips. These are usually kept in check by our immune system. They are more likely to lead to cold sores if your immune system is weakened. The main possible triggers are:

Most of these potential triggers can't be avoided, or are difficult to avoid. There is a lack of good research on whether cold sores can be prevented by steering clear of avoidable triggers, such as tanning beds and strenuous sports.

Some people think that the feeling of disgust can trigger cold sore outbreaks. But there is no scientific proof that this is true.

Can medication prevent cold sores?

If someone has very frequently recurring cold sores, doctors may suggest preventive treatment with systemic medication that inhibits the replication of viruses. “Systemic” means that the medication enters the bloodstream and travels around the body, unlike local treatment. Examples of this kind of medication include acyclovir, famciclovir and valacyclovir. Also known as antiviral drugs, these medications are usually taken as tablets. Studies have mainly focused on the drug acyclovir.

Depending on the aim of treatment, medications for the prevention of cold sore outbreaks can be used over the short term or long term.

  • In short-term treatment with antiviral drugs, the medication is taken for about one week in order to try to prevent a cold sore outbreak – for instance, shortly before and during a skiing trip, which involves both strenuous physical activity and exposure to bright sunlight.
  • In long-term treatment, the medication is taken over several months in order to reduce the number of outbreaks.

Research on short-term treatment

There are only a few studies in this area, on the short-term use of acyclovir for the prevention of cold sores in people who have a healthy immune system. There is no proof that the short-term use of antiviral drugs can prevent outbreaks.

Research on long-term treatment

Only one study has looked into whether acyclovir can prevent cold sores when taken over a longer period of time. The people who took part in the study had more than five cold sores per year. They took the medication twice a day over a period of four months, at a total daily dose of 800 mg. This is what was found after the four months:

  • The participants who only took a placebo (fake medication) had an average of two cold sores during that time.
  • Those who took acyclovir had an average of one cold sore in the four months.

In other words, the long-term use of acyclovir reduced the number of cold sore outbreaks by half. But because this outcome is based on only one small study involving 22 people, it is fairly unreliable.

Acyclovir is a well-tolerated drug. There is a lack of good research into the possible risks associated with its long-term use, though. People who have kidney failure are advised to take lower doses and have regular kidney check-ups in order to avoid potential complications.

Does medication protect people with a weakened immune system?

Six studies looked into whether acyclovir can prevent cold sores in people with a weakened immune system. The participants had cancer treatment with chemotherapy or a bone marrow transplant during the studies. They also took acyclovir two to five times per day over 4 to 11 weeks. The maximum dose was 2,000 mg per day.

The results showed that acyclovir prevented cold sores in about half of the people while they were having the cancer treatment. So antiviral drugs can clearly reduce the risk of cold sore outbreaks in people who have a weakened immune system. They can also reduce the severity of outbreaks if someone gets a cold sore.

What are the other treatment options?

Topical treatments (applied from the outside) with antiviral creams, gels or ointments haven’t been proven to prevent cold sores. Experts believe that these medications can’t prevent cold sores because they don’t reach the affected nerve cells.

There is also hardly any research on other treatments such as lysine, laser treatment, hypnosis and applying heat topically. So it isn’t known whether they can help.


  • Chi CC, Wang SH, Delamere FM et al. Interventions for prevention of herpes simplex labialis (cold sores on the lips). Cochrane Database Syst Rev 2015; (8): CD010095. [PMC free article: PMC6461191] [PubMed: 26252373]
  • Glenny AM, Fernandez Mauleffinch LM, Pavitt S et al. Interventions for the prevention and treatment of herpes simplex virus in patients being treated for cancer. Cochrane Database Syst Rev 2009; (1): CD006706. [PubMed: 19160295]
  • IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

    Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. informedhealth.org can provide support for talks with doctors and other medical professionals, but cannot replace them. We do not offer individual consultations.

    Our information is based on the results of good-quality studies. It is written by a team of health care professionals, scientists and editors, and reviewed by external experts. You can find a detailed description of how our health information is produced and updated in our methods.

© IQWiG (Institute for Quality and Efficiency in Health Care)
Bookshelf ID: NBK525765


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