Ramalho K.M. et al. - Photobiomodulation and Recurrences of Cold Sores: A Systematic Review

This systematic review included only 3 randomized trials on the prevention of cold sore recurrences using photobiomodulation. Two trials reported fewer recurrences, one found no difference, and the certainty of the evidence is considered low.

What this study measured

Cold sores, or fever blisters, recur in many people at varying intervals. This review seeks to determine whether photobiomodulation—that is, the application of low-intensity light—can reduce these recurrences.

Karen Müller Ramalho and her colleagues conducted a systematic review using the PICOS framework, limited to randomized clinical trials. PubMed, Embase, Scopus, the Cochrane Library, the Virtual Health Library, and gray literature were searched. Nine publications were reviewed in full text, and three studies met the eligibility criteria. This is a qualitative review: no numerical meta-analysis is reported in the abstract.

Key Findings

The three essays do not all point in the same direction, and the authors emphasize this.

• Recurrence rate: Two trials report a decrease following photobiomodulation compared with comparator treatments
• A trial found no difference in the rate of recurrence
• Severity and Duration of Episodes: Inconsistent Results Across Studies
• Safety: No adverse events were reported in the studies that provided safety data
• Strength of evidence: low

How photobiomodulation works for this indication

The review’s abstract does not describe a mechanism. Generally speaking, it is assumed that red or near-infrared light affects the mitochondria in cells and inflammation signaling, which could influence the response of the skin and mucous membranes. For cold sores, these theories remain hypotheses: the review assesses the frequency of recurrences, not the mechanism.

Limits You Should Know

There are significant limitations. Only three trials were included, all with small sample sizes, and the blinding of the assessment was incomplete. Laser settings and comparator treatments varied across trials. One of the three trials showed no benefit. The authors rate the certainty of the evidence as low and believe that these limitations preclude any definitive clinical recommendation. The summary does not provide figures on the extent of the reduction in recurrence, the duration of follow-up, or the optimal light parameters. It is therefore impossible to know which wavelength, dose, or treatment frequency would be most appropriate.

What This Means in Practice

In practical terms, a person prone to recurrent episodes should not view this review as proof of effectiveness. Above all, it shows that the subject is being studied and that the available results are encouraging but preliminary. Any decision regarding treatment should be made in consultation with a doctor or dentist, who can recommend established treatment options.

These findings suggest that photobiomodulation could be explored as a complementary approach to reducing recurrences of cold sores, although it cannot be recommended at this stage. It is not a substitute for antiviral treatments prescribed by a doctor or dentist. The authors call for better-designed trials with standardized protocols and outcome measures.

Frequently Asked Questions

Does photobiomodulation prevent recurrent cold sores?

The results are mixed. Of three trials, two report fewer recurrences, and one finds no difference. The authors suggest a possible reduction, but the certainty of the evidence is low.

Is photobiomodulation safe for this indication?

No adverse events were reported in the studies that provided safety data. However, the number of trials and participants remains very limited.

Can it replace antiviral treatment?

No. This review does not compare photobiomodulation to antiviral medications and does not suggest that it can be used as a substitute for prescribed treatment. Talk to a healthcare professional.

Reference

Ramalho KM, Santos NDD, Siqueira JM, Horliana ACRT, Eduardo CP, Bezinelli LM, Eduardo FP, Araújo ALD. Can photobiomodulation prevent recurrences of herpes labialis? A systematic review. Einstein (São Paulo), 2026. PMID 42752735. View the study on PubMed

This summary is provided for informational purposes only and does not constitute medical advice. Photobiomodulation is not a substitute for prescribed treatment. Consult a healthcare professional.