Measures for preventing cold sores

Review question

What measures are effective in preventing recurrence of cold sores?


A cold sore is an irritating recurrent viral infection with no proven cure. It gives rise to painful vesicles on the lips that form unsightly crusts, causing an unpleasant look and mental distress. We aimed to examine the effects of available measures for preventing recurrence of cold sores in people with normal immunity.

Study characteristics

We examined the research published up to 19 May 2015. We wanted to include studies only if receiving one preventative measure or another was decided by chance. This research method, termed randomised controlled trial (RCT), is the best way to test that a preventive effect is caused by the measure being tested. We found 32 RCTs that included 2640 people and examined 19 preventative measures. The drug manufacturer funded a total of 18 out of 32 studies, non-profit organisations funded 4, and we do not know how the other 10 were funded.

Key results

Long-term use of antiviral drugs taken by mouth prevented cold sores, though with a very small decrease of 0.09 episodes per person per month. The preventative effect of long-term use of aciclovir cream applied to the lips was uncertain. Long-term use of 1,5-pentanediol gel and 2-hydroxypropyl-β-cyclo dextrin 20% gel applied to the lips did not prevent cold sores.

Short-term use of either antiviral drugs or creams did not prevent cold sores. Neither short-term nor long-term use of these antiviral drugs or creams appeared to cause side-effects.

The preventative effects of sunscreen were uncertain. Application of sunscreen prevented cold sores induced by experimental ultraviolet light, but did not prevent cold sores induced by sunlight.

We found very little evidence about the preventative effects of thymopentin, low-energy laser, and hypnotherapy for cold sores. The available evidence found no preventative effects of lysine, LongoVital® supplementation, gamma globulin, herpes virus vaccine, and yellow fever vaccine. There were no consistent data to confirm that levamisole and interferon do prevent cold sores.

These studies found no increase in adverse events related to the use of topical antiviral agents.

Quality of the evidence

The quality of the evidence was low to moderate for most outcomes, but was very low for some outcomes.

Authors' conclusions: 

The current evidence demonstrates that long-term use of oral antiviral agents can prevent HSL, but the clinical benefit is small. We did not find evidence of an increased risk of adverse events. On the other hand, the evidence on topical antiviral agents and other interventions either showed no efficacy or could not confirm their efficacy in preventing HSL.

Read the full abstract...

Herpes simplex labialis (HSL), also known as cold sores, is a common disease of the lips caused by the herpes simplex virus, which is found throughout the world. It presents as a painful vesicular eruption, forming unsightly crusts, which cause cosmetic disfigurement and psychosocial distress. There is no cure available, and it recurs periodically.


To assess the effects of interventions for the prevention of HSL in people of all ages.

Search strategy: 

We searched the following databases up to 19 May 2015: the Cochrane Skin Group Specialised Register, the Oral Health Group Specialised Register, CENTRAL in the Cochrane Library (Issue 4, 2015), MEDLINE (from 1946), EMBASE (from 1974), LILACS (from 1982), the China National Knowledge Infrastructure (CNKI) database, Airiti Library, and 5 trial registers. To identify further references to relevant randomised controlled trials, we scanned the bibliographies of included studies and published reviews, and we also contacted the original researchers of our included studies.

Selection criteria: 

Randomised controlled trials (RCTs) of interventions for preventing HSL in immunocompetent people.

Data collection and analysis: 

Two authors independently selected trials, extracted data, and assessed the risk of bias. A third author was available for resolving differences of opinion.

Main results: 

This review included 32 RCTs, with a total of 2640 immunocompetent participants, covering 19 treatments. The quality of the body of evidence was low to moderate for most outcomes, but was very low for a few outcomes. Our primary outcomes were 'Incidence of HSL' and 'Adverse effects during use of the preventative intervention'.

The evidence for short-term (≤ 1 month) use of oral aciclovir in preventing recurrent HSL was inconsistent across the doses used in the studies: 2 RCTs showed low quality evidence for a reduced recurrence of HSL with aciclovir 400 mg twice daily (risk ratio (RR) 0.26, 95% confidence interval (CI) 0.13 to 0.51; n = 177), while 1 RCT testing aciclovir 800 mg twice daily and 2 RCTs testing 200 mg 5 times daily found no similar preventive effects (RR 1.08, 95% CI 0.62 to 1.87; n = 237; moderate quality evidence and RR 0.46, 95% CI 0.20 to 1.07; n = 66; low quality evidence, respectively). The direction of intervention effect was unrelated to the risk of bias. The evidence from 1 RCT for the effect of short-term use of valaciclovir in reducing recurrence of HSL by clinical evaluation was uncertain (RR 0.55, 95% CI 0.23 to 1.28; n = 125; moderate quality evidence), as was the evidence from 1 RCT testing short-term use of famciclovir.

Long-term (> 1 month) use of oral antiviral agents reduced the recurrence of HSL. There was low quality evidence from 1 RCT that long-term use of oral aciclovir reduced clinical recurrences (1.80 versus 0.85 episodes per participant per a 4-month period, P = 0.009) and virological recurrence (1.40 versus 0.40 episodes per participant per a 4-month period, P = 0.003). One RCT found long-term use of valaciclovir effective in reducing the incidence of HSL (with a decrease of 0.09 episodes per participant per month; n = 95). One RCT found that a long-term suppressive regimen of valaciclovir had a lower incidence of HSL than an episodic regimen of valciclovir (difference in means (MD) -0.10 episodes per participant per month, 95% CI -0.16 to -0.05; n = 120).

These trials found no increase in adverse events associated with the use of oral antiviral agents (moderate quality evidence).

There was no evidence to show that short-term use of topical antiviral agents prevented recurrent HSL. There was moderate quality evidence from 2 RCTs that topical aciclovir 5% cream probably has little effect on preventing recurrence of HSL (pooled RR 0.91, 95% CI 0.48 to 1.72; n = 271). There was moderate quality evidence from a single RCT that topical foscarnet 3% cream has little effect in preventing HSL (RR 1.08, 95% CI 0.82 to 1.40; n = 295).

The efficacy of long-term use of topical aciclovir cream was uncertain. One RCT found significantly fewer research-diagnosed recurrences of HSL when on aciclovir cream treatment than on placebo (P < 0.05), but found no significant differences in the mean number of participant-reported recurrences between the 2 groups (P ≥ 0.05). One RCT found no preventive effect of topical application of 1,5-pentanediol gel for 26 weeks (P > 0.05). Another RCT found that the group who used 2-hydroxypropyl-β-cyclo dextrin 20% gel for 6 months had significantly more recurrences than the placebo group (P = 0.003).

These studies found no increase in adverse events related to the use of topical antiviral agents.

Two RCTs found that the application of sunscreen significantly prevented recurrent HSL induced by experimental ultraviolet light (pooled RR 0.07, 95% CI 0.01 to 0.33; n = 111), but another RCT found that sunscreen did not prevent HSL induced by sunlight (RR 1.13, 95% CI 0.25 to 5.06; n = 51). These RCTs did not report adverse events.

There were very few data suggesting that thymopentin, low-level laser therapy, and hypnotherapy are effective in preventing recurrent HSL, with one to two RCTs for each intervention. We failed to find any evidence of efficacy for lysine, LongoVital® supplementation, gamma globulin, herpes simplex virus (HSV) type I subunit vaccine, and yellow fever vaccine in preventing HSL. There were no consistent data supporting the efficacy of levamisole and interferon, which were also associated with an increased risk of adverse effects such as fever.