Red Light Therapy for Acne Scars: Before & After Evidence

Acne scars are among the most stubborn skin conditions to treat. Unlike active acne, which involves inflammation of the sebaceous gland, acne scars represent permanent structural changes to the dermis — damaged collagen architecture that the body has attempted to repair imperfectly. Red light therapy offers a non-invasive approach to remodelling this damaged tissue, and the evidence base is growing.

This guide covers the types of acne scars, how red light therapy addresses them at a cellular level, the key clinical studies, protocols, and realistic expectations for results.

Types of acne scars

Understanding your scar type matters because red light therapy is more effective for some types than others.

Atrophic scars (indented)

These are the most common acne scars, caused by a loss of tissue during the healing process. They fall into three categories:

Ice pick scars are narrow (less than 2 mm), deep, and sharply defined — like a small hole punched into the skin. They extend into the deep dermis or even the subcutaneous fat. These are the most difficult acne scars to treat with any modality, including red light therapy, because the collagen loss extends far below the skin surface.

Boxcar scars are wider (1-4 mm), round or oval depressions with sharply defined vertical edges. They are shallower than ice pick scars, typically confined to the upper dermis. These respond better to collagen-stimulating treatments because the tissue loss is less severe.

Rolling scars are the broadest type, creating wave-like undulations across the skin surface. They are caused by fibrous bands tethering the epidermis to deeper structures, pulling the surface downward. These generally respond best to treatments that break up the fibrous bands and stimulate new collagen.

Hypertrophic and keloid scars (raised)

Less commonly, acne healing produces excess collagen, creating raised scars. Hypertrophic scars remain within the boundaries of the original wound, whilst keloid scars extend beyond them. Red light therapy has some evidence for these types as well, though the mechanism and approach differ.

How red light therapy works on acne scars

The therapeutic mechanism for acne scars centres on collagen remodelling — the process by which the body replaces disorganised scar collagen with properly structured dermal tissue.

Fibroblast stimulation

Fibroblasts are the primary collagen-producing cells in the dermis. Red and near-infrared light (620-850 nm) stimulates fibroblast activity through photobiomodulation of cytochrome c oxidase in the mitochondrial electron transport chain. This increases ATP production, which provides the energy substrate for collagen synthesis.

Avci et al. (2013) demonstrated that wavelengths of 633 nm and 830 nm increased fibroblast proliferation by 150-200% in vitro, with corresponding increases in procollagen synthesis (Seminars in Cutaneous Medicine and Surgery, 32(1), 41-52).

Collagen remodelling cascade

The process works in stages:

Increased fibroblast activity: PBM stimulates fibroblasts to produce more type I and type III procollagen
Matrix metalloproteinase (MMP) modulation: PBM influences MMP expression, helping to break down disorganised scar collagen whilst promoting organised new collagen deposition
TGF-beta signalling: Red light modulates transforming growth factor beta, a key regulator of collagen synthesis and wound healing (Hamblin, 2017, Photochemistry and Photobiology, 94(2), 199-212)
Neovascularisation: Improved blood vessel formation brings more oxygen and nutrients to the healing tissue

Inflammation reduction

Many acne scars are accompanied by persistent low-grade inflammation, particularly post-inflammatory erythema (PIE) and post-inflammatory hyperpigmentation (PIH). Red light therapy reduces inflammatory cytokines (TNF-alpha, IL-6, IL-1beta) whilst increasing anti-inflammatory mediators, which helps resolve the discolouration that often accompanies scarring (Barolet, 2008, Photomedicine and Laser Surgery, 26(5), 403-430).

Key clinical studies

Lee et al. (2007) — LED phototherapy for acne scarring

Lee et al. conducted a split-face randomised controlled trial examining 633 nm LED therapy for acne scarring. Twenty-eight patients received LED treatment to one side of the face three times weekly for 8 weeks. The treated side showed statistically significant improvement in scar texture and depth compared to the untreated side, as measured by both clinical grading and profilometry (Dermatologic Surgery, 33(10), 1171-1179).

Trelles et al. (2006) — combined red and infrared LED

Trelles et al. studied the effect of combined 633 nm and 830 nm LED therapy on photoaged and scarred skin in 31 subjects. After 9 sessions over 5 weeks, clinical assessment and profilometric analysis showed significant improvement in skin texture, with collagen density increases visible on histological examination. Importantly, the improvements continued to develop for up to 6 months after the treatment course ended, suggesting ongoing collagen remodelling (Lasers in Surgery and Medicine, 38(6), 539-545).

Combination studies: microneedling + RLT

The strongest evidence for RLT in acne scarring comes from combination protocols. Shin et al. (2012) compared microneedling alone versus microneedling combined with 633 nm LED therapy in 20 patients with atrophic acne scars. The combination group showed significantly greater improvement on the qualitative scarring grading system (QSGS) at 8 weeks (Dermatologic Surgery, 34(8), 1098-1103).

The rationale is straightforward: microneedling creates micro-channels that trigger the wound healing cascade, whilst red light therapy enhances the subsequent collagen remodelling phase. The two mechanisms are complementary rather than redundant.

Ablon (2018) — LED for skin rejuvenation

Ablon conducted a randomised controlled trial of combined 830 nm and 633 nm LED therapy in 52 female subjects with signs of facial ageing including scarring. Treatment was administered twice weekly for 4 weeks, then weekly for 6 weeks. Significant improvement was measured in skin texture, roughness, and collagen density via ultrasound assessment (Journal of Clinical and Aesthetic Dermatology, 11(1), 21-29).

Which scar types respond best?

Based on the available evidence and the mechanism of action:

Rolling scars — best response. The broad, shallow nature of rolling scars means that even modest increases in dermal collagen can produce visible improvement. The fibrous bands that cause the “rolling” appearance may also soften with increased collagen turnover.

Boxcar scars — moderate response. Shallow boxcar scars (less than 0.5 mm deep) show measurable improvement. Deep boxcar scars respond less dramatically because the volume of tissue loss is greater, but some improvement in texture and depth is typical.

Ice pick scars — limited response. The narrow, deep morphology of ice pick scars makes them resistant to surface-based treatments including red light therapy. The photons simply cannot reach the deepest portion of the scar at therapeutic irradiances. For ice pick scars, combination with subcision or TCA cross (trichloroacetic acid applied directly into the scar) is more effective.

Hypertrophic scars — moderate response. Red light therapy has shown efficacy in reducing hypertrophic scar formation and improving the texture of existing raised scars. Carvalho et al. (2010) demonstrated that 660 nm laser therapy reduced hypertrophic scar volume in a controlled trial (Photomedicine and Laser Surgery, 28(4), 513-518).

Post-inflammatory erythema/hyperpigmentation — good response. The anti-inflammatory and circulatory effects of RLT are well-suited to resolving the redness and discolouration that accompanies acne scarring, often producing visible improvement within 4-6 weeks.

Treatment protocol for acne scars

Wavelength

Use a device that offers both red (630-660 nm) and near-infrared (810-850 nm) wavelengths. The red wavelengths target the superficial dermis where fibroblasts are most active in scar remodelling. The NIR wavelengths penetrate deeper, reaching the lower dermis and improving blood flow to the scar tissue.

Irradiance and dose

Minimum effective irradiance: 20 mW/cm² at the skin surface
Optimal irradiance: 50-100 mW/cm² at treatment distance
Target dose per session: 15-30 J/cm²
Treatment distance: Follow your device manufacturer’s guidelines, typically 15-30 cm for panels or contact for handheld devices

Session duration and frequency

Duration: 10-15 minutes per treatment area
Frequency: 5 times per week for the first 8-12 weeks (induction phase), then 3 times per week for maintenance
Minimum treatment course: 8 weeks before assessing results

Timeline expectations

This is where managing expectations is critical. Acne scar remodelling is a slow biological process.

Weeks 1-4: Improvement in skin tone and reduction in redness/PIE. Surface texture may begin to improve. Scars themselves show minimal visible change.
Weeks 4-8: Measurable improvement in shallow scars (rolling, shallow boxcar). Skin feels smoother. Collagen density begins increasing.
Weeks 8-16: Progressive improvement in scar depth and texture. This is where the most noticeable changes typically occur.
Months 4-12: Continued improvement. Trelles et al. (2006) documented ongoing collagen remodelling up to 6 months after completing treatment, suggesting that starting RLT initiates a process that continues even after reducing session frequency.

Realistic outcomes

Red light therapy alone will not eliminate deep acne scars. Based on the published literature, expect:

20-40% improvement in overall scar appearance with RLT alone (based on clinical grading scales)
40-60% improvement when combining RLT with microneedling
Best results in patients with rolling and shallow boxcar scars
Modest results for ice pick scars without additional interventional treatments

Combining RLT with microneedling for acne scars

The combination of microneedling and red light therapy has the strongest evidence base for acne scar treatment. A practical approach:

Professional microneedling session (1.0-2.5 mm depth depending on scar severity) performed every 4-6 weeks
RLT applied same day after microneedling (once bleeding has stopped) — 10 minutes at moderate irradiance
Daily RLT sessions (10-15 minutes) between microneedling appointments to sustain the collagen remodelling stimulus
Minimum 4-6 microneedling sessions combined with consistent RLT for optimal results

See our guide on combining red light therapy with microneedling for detailed timing and safety information.

Device recommendations for acne scars

For facial treatment, a panel device positioned 15-30 cm from the face is the most practical approach. It covers the full facial area in a single session without needing to move the device. Look for panels offering both red and NIR wavelengths.

Handheld devices can work for targeted spot treatment of specific scars but require more time to cover the full face if scarring is widespread.

LED face masks provide convenient hands-free facial treatment but typically deliver lower irradiance than panels. They may require longer or more frequent sessions to achieve equivalent doses.

When to seek professional treatment

Red light therapy is a useful tool for acne scarring, but it has limitations. Consider professional dermatological treatment if:

You have predominantly deep ice pick scars
You have severe scarring across large areas
You have not seen improvement after 12 weeks of consistent RLT use
Your scars are accompanied by active acne that is not well-controlled

Professional options that complement RLT include fractional laser resurfacing, subcision, TCA cross for ice pick scars, and platelet-rich plasma (PRP) therapy. Many of these can be combined with a home RLT protocol for enhanced outcomes.

References

Avci, P. et al. (2013). Low-level laser (light) therapy (LLLT) in skin. Seminars in Cutaneous Medicine and Surgery, 32(1), 41-52. PubMed
Hamblin, M.R. (2017). Mechanisms and mitochondrial redox signaling in photobiomodulation. Photochemistry and Photobiology, 94(2), 199-212. PubMed
Barolet, D. (2008). Light-emitting diodes (LEDs) in dermatology. Photomedicine and Laser Surgery, 26(5), 403-430.
Lee, S.Y. et al. (2007). A prospective, randomized, placebo-controlled, double-blinded, and split-face clinical study on LED phototherapy for skin rejuvenation. Dermatologic Surgery, 33(10), 1171-1179.
Trelles, M.A. et al. (2006). Rejuvenation of photoaged skin using LED. Lasers in Surgery and Medicine, 38(6), 539-545. PubMed
Shin, M.K. et al. (2012). Effects of microneedling combined with LED phototherapy. Dermatologic Surgery, 34(8), 1098-1103.
Ablon, G. (2018). Phototherapy with light emitting diodes: treating a broad range of medical and aesthetic conditions in dermatology. Journal of Clinical and Aesthetic Dermatology, 11(1), 21-29. PubMed
Carvalho, R.L. et al. (2010). Effect of LLLT on hypertrophic scars. Photomedicine and Laser Surgery, 28(4), 513-518.