Red Light Therapy for Cold Sores: Scientific Evidence

Pairing antimicrobial photodynamic therapy (aPDT), which uses a dye activated by light, with photobiomodulation, a 2020 case series described 3 patients with cold sores on the lip. A 0.01% methylene blue dye was used for the aPDT stage because it absorbs red light, and photobiomodulation was then applied to the lip once a crust had formed to encourage more organized repair tissue. Tissue repair was complete after 7 days in the cases described. The authors concluded that lasers appear to be a workable alternative for cold sores, applied differently depending on the stage of the outbreak.

Published in 2018, this systematic review examined whether laser therapy helps treat and prevent recurring cold sores. 6 clinical trials were selected from 227 articles, using red and near-infrared light from 632.5 to 870 nm applied to the lip and face in sessions of 40 seconds to 10 minutes, across courses of 6 to 16 sessions, at 2.04 to 48 J/cm². Because the available data varied too much to combine statistically, the studies were assessed in descriptive terms only. The authors concluded that laser therapy appeared to reduce pain and the frequency with which cold sores returned, with no side effects reported.

Researchers in Iran compared a diode laser against aciclovir cream and a switched-off laser for recurring cold sores in a 2017 single-blind randomized trial. 60 patients were divided equally into 3 groups of 20, with the laser group receiving near-infrared light at 870 nm and 4.5 J/cm² in 60-second sessions over 6 days, held about 0.236 to 0.315 inches from the lip. Recovery took 2.2 days with the laser, compared with 3.4 days with the cream and 4.3 days with the switched-off device, a statistically significant difference across the 3 groups. The researchers reported that pain eased faster with the laser as well.

This 2014 observational study described a 7-year-old girl treated with low-level laser therapy (LLLT) for a recurring cold sore on the lower lip, which had appeared 24 hours earlier and was causing enough pain to disturb her eating and sleep. An infrared diode laser at 780 nm and 70 mW was applied to 4 points on the sore for 80 seconds each, at 5 J/cm² per point and 20 J/cm² per session, in 3 sessions given 24 hours apart. By the second session, the pain and itching had gone, the redness appeared reduced, and the blisters were drying into scabs. The lip appeared almost fully healed at a follow-up 10 days after the first session, with no sign of the virus reactivating.

Cold sores cleared roughly 2 days sooner with infrared light than with a sham device, according to a 2013 randomized placebo-controlled trial in the United Kingdom. 87 patients with recurring cold sores received 3-minute treatments to the lip from a light-emitting diode device at 1072 nm and 600 Hz, 3 times a day for 2 days, or an identical sham unit. The trial found median healing took 129 hours with the light against 177 hours with the sham, a statistically significant difference, while the time taken for a crust to form did not differ between the groups.

A preventive protocol gave each of 3 patients repeated laser sessions twice a week in a 2012 observational study of recurring cold sores, followed for 3 years. Red and near-infrared light at 660, 7,80 and 830 nm was applied in contact with the lips, the skin around the mouth, the base of the nose, and the chin at 40 to 70 mW and 4 to 20 J/cm², with a higher-powered 1064 nm laser at 1.5 W and 15 Hz used to drain blisters when they appeared. Outbreaks appeared less frequently and healed faster across the follow-up period, and in many cases no sign of infection could be found the following day.

Across 554 patients pooled from 2 consecutive studies, a 2012 clinical trial in Cuba examined low-level laser therapy (LLLT) for repeated cold sores. 232 patients received either red light at 670 nm, 40 mW, 1.6 J and 2.04 J/cm² per blister in the earliest stage, rising to 4.8 J once a crust had formed, plus 1.2 J applied to the upper spine, or conventional care including aciclovir, and a further 322 treated patients were then followed for 5 years. Both initial healing and the length of time before cold sores returned appeared to improve with the light. The authors concluded that LLLT is an effective option, with no side effects observed.

When 2 patients with repeated cold sores declined further antiviral treatment, a 2011 observational study in Brazil offered low-level laser therapy (LLLT) instead. A 23-year-old man with 5 outbreaks below the lower lip in a single year received 4 sessions, and a 50-year-old woman with 5 years of outbreaks around the mouth received 5 sessions, each session delivering red light at 660 nm and 100 mW for 8 seconds per point at 30 J/cm², spread across 4 points around the sore in the first case and 12 in the second. Sores cleared after 7 days in the man and after 5 days in the woman. According to the report, neither patient had a recurrence during 17 months of follow-up.

1 patient whose pain disappeared after a single treatment took part in a 2010 observational study combining 2 lasers for a severe cold sore infection on the lower lip. A high-intensity laser at 2.94 µm and 80 mJ per pulse was used alongside a low-intensity red laser at 660 nm, 3.8 J/cm² and 10 mW, with no medicines taken by mouth or applied to the skin during treatment. The infection appeared healed by day 10, and a further outbreak followed about 40 days later.

Cold sores healed in 6.3 days with light against 9.4 days with a placebo device, in a 2006 randomized double-blind trial of an over-the-counter cold sore unit. 32 patients used a light-emitting diode device giving near-infrared light at 1072 nm to the lip, in at least 6 treatments of 3 minutes each. The time taken for a crust to form also appeared shorter with the light, at 2 days against 2.88 days, though that difference did not reach statistical significance.

Comparing a single 5-minute light treatment against aciclovir cream applied 5 times a day, a 2001 randomized double-blind trial in the United Kingdom examined cold sores on the lip. 51 patients began treatment within 36 hours of their first symptoms and received either near-infrared light at 1072 nm, 5 to 10 mW/cm² and 600 Hz, or the cream. Cold sores treated with light healed in 4.3 days, compared with 8.5 days with the cream, a statistically significant difference. The trial found that a single session was enough to shorten healing by about 4 days.

A 1999 randomized double-blind placebo-controlled trial evaluated low-intensity laser therapy for repeated cold sores around the mouth. 50 patients who had at least 1 outbreak a month for more than 6 months were randomly assigned to red light at 690 nm, 80 mW/cm,² and 48 J/cm² applied to the lips and the skin around the mouth daily for 2 weeks, or to a sham device, and 48 of them were followed for 52 weeks. The median time before cold sores returned was 37.5 weeks in the laser group, appearing longer than in the sham group. No side effects of any kind were noted.

Whether photobiomodulation therapy (PBMT) speeds recovery as well as easing pain was examined in a 2024 randomized double-blind controlled trial of recurring cold sores. 40 patients were split evenly, with 20 receiving red light at 650 nm, 100 mW, and 4.7 J/cm² to the lip in 2-minute sessions over 5 days, and 20 receiving aciclovir. The trial found pain significantly lower in the light group after the second session and resolving sooner overall, but no difference between the groups in how quickly the cold sores healed.

71 adults whose cold sores had returned for at least 3 years took part in a 2010 trial of laser phototherapy for prevention, run in Brazil. 41 received near-infrared light at 780 nm and 60 mW, at 3 or 4.5 J/cm², to both the upper and lower lips, treating unaffected skin as well as active sores, in 1 session per week for 10 weeks, while 30 used aciclovir cream. According to the trial, the light group developed smaller cold sores and less swelling than the cream group, both differences reaching statistical significance. Reductions in pain and in how often outbreaks returned weren’t significant enough.