Can cold sore outbreaks be prevented?

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:

• Sunlight and artificial UV light
• Common colds
• Fever
• Minor injuries and cracks in the lips
• Physical strain
• Emotional stress
• Using steroids
• Hormonal fluctuations, for example during women’s monthly period

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.

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 valaciclovir. 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.

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.

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.

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.

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.