Red Light Therapy

What it is

Red light therapy, also called photobiomodulation or low-level light therapy, shines low-power red or near-infrared light from lasers or LEDs on the skin or scalp [1]. Hair devices come as combs, helmets and hats, and clinic lasers are used for mouth sores during cancer care [2][3][4].

What the research says

Pattern hair loss. A 2021 meta-analysis of 15 studies (795 people) found more hair density with photobiomodulation than control (standardised mean difference 1.02, 95% CI 0.68 to 1.36) [2]. A 2025 meta-analysis of 38 studies (3,098 people, mostly with androgenetic alopecia) reported a higher hair density after 4 to 26 weeks (standardised mean difference 1.14 under 20 weeks and 1.44 over 20 weeks), with high variation between studies [5]. A 2017 meta-analysis of randomized trials found light therapy in men was superior to placebo, as were minoxidil and finasteride, with high heterogeneity [6]. In a sham-controlled trial of 41 men, a 655 nm device raised hair counts by 67.2 versus 28.4 with sham [7]; in 42 women the rise was 100.3 versus 23.9 [8]. A helmet trial found hair density rose by 41.90 hairs per cm versus 0.72 with sham over 16 weeks [9]. In a 24-week trial of 100 people, hair coverage was 14.2% on the treated side versus 11.8% on the sham side [10]. In women, light therapy was comparable to 5% minoxidil, with the combination best, in a 4-month trial [11]. A meta-analysis of minoxidil combinations (15 studies, 1,172 people) found that adding light therapy, finasteride or microneedling to minoxidil beat minoxidil alone on global photographic assessment, and light therapy and microneedling also increased hair count [12].

Mouth sores from cancer treatment (oral mucositis). A 2024 meta-analysis of 14 randomized trials (869 head and neck cancer patients) found the incidence of mucositis was lower from the second week (risk ratio 0.49, 95% CI 0.25 to 0.97), severe mucositis was about half as common by the end of treatment (RR 0.45, 0.24 to 0.85), and pain was lower [4]. Another meta-analysis of 6 trials reported a risk ratio of 0.36 (0.29 to 0.44) for debilitating lesions [13].

Wounds and diabetic foot ulcers. A meta-analysis of 7 randomized trials (194 people) found ulcers were more likely to heal completely with low-level light therapy (odds ratio 6.72, 95% CI 1.99 to 22.64), and no treatment-related adverse events were reported [14]. A meta-analysis of 12 trials found ulcers were 4.65 times more likely to heal, but could not recommend the best treatment settings [15]. A 2021 meta-analysis found very low-certainty evidence that it prevents severe radiation dermatitis (grade 3 RR 0.21, 0.05 to 0.94) [16].

Pain. A meta-analysis of 9 trials (325 people) found low-level laser eased fibromyalgia pain versus placebo (standardised mean difference 1.18, 0.82 to 1.54), but the trials were of low to middle quality, and laser plus exercise gave no extra advantage over exercise alone [17]. For Achilles tendinopathy, 4 trials (119 people) gave low to very low certainty evidence, insufficient to support routine use [18].

Wrinkles. In a 12-week trial of 52 women, red (660 nm) and white LEDs both improved wrinkles around the eyes, with no statistically significant difference between them and no placebo group [19].

Expert consensus. A 2025 consensus of 21 experts judged photobiomodulation effective for peripheral neuropathy, androgenic alopecia, wound ulcers, pressure ulcers, diabetic foot ulcer pain and acute radiation dermatitis [1].

Doses used in studies

Hair trials used 655 nm devices [7], a helmet emitting 630, 650 and 660 nm for 18 minutes a day for 24 weeks [3], 30 minutes three times a week for 24 weeks [10], or 25 minutes three days a week for 4 months [11]. Mouth-sore trials got the best results from clinic helium-neon or InGaAlP lasers at 10 to 25 mW [4]. A wrinkle trial used 5.17 J of red or white LED light daily for 12 weeks [19].

Safety and interactions

Common side effects. The 2025 consensus judged photobiomodulation a safe treatment for adults, and red light does not induce DNA damage [1]. The hair trials reported no adverse events or side effects [7][8], and no serious adverse events [10]. Treatment-related adverse events were not reported in the diabetic foot ulcer trials [14].

Cancer. A systematic review of oncologic safety found no clinical trial data linking photobiomodulation with adverse events, including a new or recurrent cancer, and no evidence to support the idea that people who have previously been treated for cancer should avoid it [20].

Upper limits and toxic doses. No upper limits were established in the studies reviewed.

Interactions. No data on interactions with medicines were found in the studies reviewed.

Pregnancy and breastfeeding. No data were found in the studies reviewed; the consensus covered adult patients [1].

Relevant conditions. People having cancer treatment, or with ulcers or neuropathy, should use it only with their care team [4][14].

Caveats and open questions

Devices, wavelengths, doses and schedules differ widely, and reviews could not identify the best settings [15][2]. Hair meta-analyses reported high heterogeneity [5][6]. Diabetic foot ulcer reviews included small trials and called for larger, better-designed studies [14][15]. Results from clinic lasers for mouth sores may not apply to home devices [4]. Wrinkle and fibromyalgia evidence comes from small trials, some without placebo groups [19][17].