Comparison of Two Intense Pulsed Light Regimens for Facial Rejuvenation: A Randomized Controlled Study

Summary

This randomized pilot study compares 80-ms and 15-ms intense pulsed light regimens for facial rejuvenation. Objective skin measures, patient-reported pain and satisfaction, and systematic adverse-event monitoring were used to assess efficacy and tolerability during three treatment sessions and 3-month follow-up.

Abstract

Intense pulsed light (IPL) is widely used for facial rejuvenation, but comparative clinical evidence for ultra-long-pulse-duration protocols remains limited. In this randomized controlled pilot trial, 27 Chinese participants with mild-to-moderate facial photoaging received three full-face IPL sessions at 4-week intervals using either an 80-ms, higher-fluence regimen (32-50 J/cm²; n = 13) or a 15-ms, lower-fluence regimen (22–30 J/cm²; n = 14). The study compares two complete regimens rather than isolating pulse width. Wrinkle percentile, pore feature count, surface sebum, R2 elasticity, and F4 viscoelasticity were measured at baseline, after each treatment, and at 1- and 3-month follow-up. The primary 3-month ANCOVA adjusted for the outcome baseline value and age, with Holm-Bonferroni correction across five objective endpoints. The nominal between-group difference favored the 80-ms regimen for pore feature count (-264.5 features; 95% CI, -466.9 to -62.1; exact p = 0.0127), but did not remain significant after Holm correction (p = 0.0635); the other objective endpoints were also not significant after correction. Pain was lower, and satisfaction was higher with 80-ms IPL. Adverse events were mild and self-limiting, with no serious adverse events, blistering, edema, pigmentary alteration, or scarring. These exploratory findings support further adequately powered trials.

Introduction

Skin aging is an intricate biological process categorized into chronological aging and exogenous aging. Chronological aging refers to the intrinsic genetic programming of skin cells, while exogenous aging results from external environmental insults, predominantly cumulative damage from ultraviolet (UV) radiation, a process termed photoaging^1,2. The clinical manifestations of facial photoaging are multifaceted, encompassing pigmentary irregularities, telangiectasia, skin roughness, fine lines, and enlarged pores³. Existing therapeutic modalities for photoaging, including chemical peels, laser therapy, and injectable agents, have been widely explored^4,5,6,7. However, these interventions are frequently associated with adverse effects such as post-inflammatory hyperpigmentation, pruritus, and edema, necessitating the exploration of safer and more efficacious alternatives.

Intense pulsed light (IPL), a non-coherent, polychromatic light source with a broad wavelength spectrum (typically 500–1200 nm), has emerged as a versatile tool in dermatological practice⁸. IPL devices emit a wide range of wavelengths that can be absorbed by various chromophores in the skin, such as melanin, hemoglobin, and water. The therapeutic efficacy and safety of IPL are governed by the principle of selective photothermolysis, which enables targeted destruction of specific structures while minimizing collateral damage to surrounding tissues⁹. This technology has gained widespread application in treating diverse skin conditions, including dyspigmentation, vascular lesions, acne, and photoaging^1,10.

The pulse width, defined as the duration of light emission, represents a critical parameter in IPL therapy. It directly influences the spatial and temporal distribution of light energy within the skin, thereby determining treatment depth, efficacy, and safety profile⁹. Conventional IPL systems typically employ pulse widths ranging from 1 to 50 milliseconds (ms). Recent technological advancements have introduced ultra-long pulse width capabilities, extending to 80 ms or even 100 ms, though standardized definitions for "long pulse width" remain elusive in the literature¹. The strategic selection of pulse width according to specific dermatological concerns is paramount: superficial pigmented lesions often respond optimally to shorter pulse widths (2–10 ms), while vascular pathologies require pulse widths commensurate with vessel diameter (3–30 ms). Hair removal procedures typically necessitate longer pulse widths (10–40 ms) due to the larger size of follicular structures⁹.

Substantial clinical evidence supports the application of IPL in managing facial photoaging¹. However, conventional pulse width configurations in standard IPL rejuvenation protocols pose elevated risks of complications, including blistering, erythema, and pigmentary alterations, particularly in individuals with darker skin phototypes⁸. The underlying mechanism involves rapid melanin-mediated absorption of light energy, where the energy delivery period of conventional pulse-width IPL falls short of the epidermal thermal relaxation time. This temporal mismatch precipitates abrupt temperature elevations in cutaneous tissues, compromising both treatment safety and patient comfort⁹.

Longer pulse durations may better accommodate the thermal relaxation behavior of deeper dermal targets, permitting more gradual heat deposition and retention in the dermis while reducing high instantaneous epidermal temperature. This is a biophysical rationale rather than a demonstrated mechanism in the present study: tissue temperatures and dermal heat retention were not measured. Technical innovations in IPL delivery systems, including sequential pulses with calibrated inter-pulse delays, can further modulate thermal deposition^8,9. Notwithstanding these advancements, comparative studies examining the differential effects of ultra-long versus conventional pulse widths in facial rejuvenation remain limited^1,11. The scientific community has identified an imperative to establish standardized protocols that maximize therapeutic outcomes while minimizing risks across diverse demographic populations. This study aims to address this knowledge gap through a systematic evaluation of the efficacy, safety, and patient comfort associated with long-pulse-width IPL compared to conventional pulse-width configurations in facial rejuvenation treatments. The findings are anticipated to contribute to the development of evidence-based, personalized treatment approaches in cosmetic dermatology.

This randomized controlled pilot study compared an 80-ms, higher-fluence regimen with a 15-ms, lower-fluence regimen for facial rejuvenation. The objectives were to evaluate changes in wrinkle percentile, pore feature count, surface sebum, R2 elasticity, and F4 viscoelasticity; compare treatment-related pain and satisfaction; and characterize adverse events. Comparative interpretations used ANCOVA adjusted for baseline outcome value and age, with confidence intervals and Holm-Bonferroni-adjusted p values.

Protocol

Ethics statement

This study was conducted in accordance with the Declaration of Helsinki and approved by the Ethics Committee of Wenzhou Hospital of Integrated Traditional Chinese and Western Medicine (approval number: 2024-L086). The trial was registered with the Chinese Clinical Trial Registry (registration number: CTR2400092254). All participants provided written informed consent before enrollment, including consent for standardized facial photography and publication of identifiable clinical facial images; the eyes were mosaicked in the published figures as an additional privacy safeguard. The workflow is depicted in Figure 1. The equipment, devices, and materials used in this protocol are listed in the Table of Materials.

Participant selection and randomization

Participants were recruited from the institutional database of patients seeking facial rejuvenation treatment between January 2024 and June 2024. Inclusion criteria required adults aged 23-55 years with Fitzpatrick skin types II–IV and visible facial photoaging. Exclusion criteria included sun exposure within 4 weeks, photosensitive disease, photosensitizing medication or topical retinoid use within the prior month, active skin infection, inflammatory skin disease, and pregnancy or lactation. To limit post-enrollment confounding by ultraviolet exposure, participants received the same broad-spectrum sunscreen and were instructed to use it daily and avoid new topical active treatments. Twenty-seven eligible participants were randomized to the 80-ms group (n = 13) or 15-ms group (n = 14) using computer-generated permuted blocks of four. Sequentially numbered opaque sealed envelopes maintained allocation concealment until enrollment.

Pre-treatment procedures

All participants underwent standardized facial cleansing without topical anesthesia. After retroauricular test spots were applied, the site was observed for 3–5 min for erythema and pain. Testing began at 32 J/cm² in the 80-ms group and 22 J/cm² in the 15-ms group. If only mild transient erythema occurred, with VAS pain ≤ 3 and no blistering or intense whitening, fluence was increased in 2 J/cm² increments. The highest tolerable fluence producing a mild thermal response without severe pain or immediate adverse effects was used within the respective 32–50 and 22–30 J/cm² ranges.

IPL treatment parameters and procedure

The study compared two complete IPL treatment regimens that differed in both pulse width and fluence; it was not designed to estimate an isolated pulse-width effect. The 80-ms regimen used 32–50 J/cm² and the 15-ms regimen used 22–30 J/cm². Both used a fixed 525-nm long-pass filter (525-1200 nm spectrum), single-pulse mode, a 2-mm layer of clear optical cooling gel, and a single non-overlapping pass with a 12 × 28 mm spot. Integrated synchronous contact sapphire cooling was used throughout. The same senior dermatologist (Y.K.; >5 years of experience with energy-based aesthetic procedures) performed all treatments. Standard post-treatment care included 15 min of cooling and daily broad-spectrum sunscreen.

Skin parameter assessment protocol

To ensure consistency in longitudinal assessment and eliminate evaluation bias, all objective skin parameter measurements and visual documentation were conducted by the same clinical research technician across all participants, who was fully certified in biophysical skin analysis and completely blinded to participants' treatment group assignments.

Biomechanical properties assessment and parameter definitions

Skin elasticity was measured with a 2-mm aperture suction probe at the forehead midline, bilateral zygomatic prominences, and bilateral masseter regions. Ten 1-second suction/1-second relaxation cycles were acquired at 450 mbar; three acquisitions per site were averaged, then the five site means were averaged to obtain one participant-level value per visit. R2 is a unitless gross-elasticity ratio (elastic recovery divided by maximum deformation); higher values indicate greater elasticity. F4 was exported by the device in mm/s and was treated in this study as a viscoelasticity index, with lower values indicating improvement. Analyses used the raw participant-level R2 and F4 values, not percentages.

Sebum production quantification and interpretation

Sebum content was quantified with a photometric sebum cassette probe at the same standardized sites after a 30-second contact. Three readings per site were averaged, then site means were averaged to obtain one participant-level value per visit. Sebum is reported in µg/cm²; lower values indicate less surface sebum. Measurements were performed at 22 ± 2 °C and 50 ± 5% relative humidity.

Standardized imaging and digital facial analysis parameters

Standardized frontal and 33° lateral images were acquired with a multispectral facial complexion analysis system under consistent positioning, lighting, and background conditions. The wrinkle outcome was a device-derived percentile on a 0–100 scale; higher values indicate fewer detected wrinkles. Pore feature count was the number of algorithm-detected pore features in the standardized region; lower values indicate improvement. The same software, capture geometry, and analysis regions were used at every visit. Image analysts were blinded to group assignment.

Anatomical and subcutaneous layer evaluation

To assess individual variation in subcutaneous tissue over bony prominences (maxilla and mandible) relative to deep-tissue sensory responses, soft-tissue thickness at the mid-cheek and lower buccal regions was evaluated during baseline 3D multispectral facial imaging and biophysical assessment. Subcutaneous thickness was estimated at standardized anatomical landmarks based on standardized cross-sectional contour mapping and high-resolution optical surface profilometry integrated into the facial analysis system. All anatomical site measurements were calibrated under standardized room conditions and evaluated by the same blinded technician.

Patient-reported outcome measures

Treatment satisfaction was assessed using a validated 5-point Likert scale (1 = very dissatisfied, 5 = very satisfied) at each follow-up visit. Pain intensity during treatment was evaluated using a digital visual analog scale (VAS: 0–10) administered immediately following each treatment session. All patient-reported outcomes were collected using standardized electronic data capture systems operating on a secure institutional database to minimize recording errors.

Safety monitoring and adverse event documentation

A comprehensive safety-monitoring protocol was used throughout the study. Erythema, edema, blistering, pigmentary change, scarring, and transient localized deep-tissue sensitivity/gum soreness were assessed and documented on a standardized adverse-event registration form. Severity, duration, and management were recorded; participants were instructed to report events between visits.

Statistical analysis plan

Analyses included all 27 randomized participants, each with complete observations at six visits. This was an exploratory pilot trial based on clinical feasibility. Continuous outcomes are summarized as mean ± standard deviation. Baseline-to-3-month within-group changes were used in paired t-tests. For each primary objective endpoint, the 3-month ANCOVA included randomized group, the corresponding baseline outcome value, and age (years) as covariates. Model-based adjusted means, standard errors, 95% confidence intervals, and exact two-sided p values are reported; differences are 80 ms minus 15 ms. Holm-Bonferroni correction controlled the family-wise error rate across wrinkle percentile, pore feature count, sebum, R2, and F4. Standardized sunscreen instructions and behavioral restrictions were used to minimize differential sun exposure, but individual ultraviolet exposure was not directly quantified. Change-score analyses were sensitivity analyses; longitudinal patterns used mixed-design repeated-measures analysis of variance with Greenhouse-Geisser correction. Patient-reported outcomes used Welch t-tests and categorical safety outcomes used Fisher exact tests.

Results

Participant demographics and baseline characteristics

All 27 randomized participants (80 ms, n = 13; 15 ms, n = 14) contributed complete data at all six visits. Mean age was 39.62 ± 9.78 years in the 80-ms group and 37.14 ± 9.31 years in the 15-ms group (p = 0.508). Twenty-five participants were female, and two were male. Baseline R2 was higher in the 80-ms group (0.721 ± 0.078 vs 0.641 ± 0.096; p = 0.023), supporting baseline-adjusted comparisons. Other obje...

Discussion

This randomized comparison does not support a claim that the 80-ms regimen is uniformly more efficacious or safer than the 15-ms regimen. Because pulse width and fluence differed together, all findings compare complete clinical regimens and cannot be attributed to pulse width alone. After adjustment for both baseline outcome value and age, no objective endpoint remained significant after Holm correction. The nominal pore-count difference and patient-reported outcomes should be viewed as exploratory signals for a larger, ...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Adverse Event Registration Form (CRF)	Institutional Clinical Trial Unit	Adverse Event Registry	Standardized case report forms to document occurrences, severity, and duration of erythema, blistering, hyperpigmentation, scarring, and gum soreness / deep-tissue sensitivity.
Broad-spectrum Sunscreen	Local Commercial Source	SPF 50, PA+++	Provided to participants for strict post-treatment daily photoprotective care.
Cooling Materials & Gel	Foshan Pingchuang Medical Technology Co., Ltd., Foshan, China	Pingzhichuang Photonic Cooling Gel	Applied topically during IPL treatment as an optical coupling and thermal protective medium.
Cutometer Probe	Courage + Khazaka Electronic GmbH, Cologne, Germany	MPA580-CUT	2 mm standard aperture probe for skin elasticity (R2, F4) measurements.
Electronic Data Capture System	Microsoft Corp., Redmond, WA, USA	Excel 2019 / Institutional EDC	Secure database used to collect patient-reported outcomes (VAS and satisfaction scores) to minimize recording errors.
IPL Device	Cynosure, Westford, MA, USA	Icon	Total spectrum: 525-1200 nm; fixed built-in 525 nm long-pass filter; spot size 12x28 mm; max fluence 90 J/cm²; integrated synchronous contact sapphire cooling.
Mild Cleanser	Local Commercial Source	N/A	Used for standardized pre-treatment facial preparation without topical anesthesia.
Randomization Tool	Microsoft Corp., Redmond, WA, USA	Excel 2019	Used for computer-generated sequence generation with block randomization.
Sebumeter Probe	Courage + Khazaka Electronic GmbH, Cologne, Germany	MPA580-SEB	Photometric cassette probe for quantifying sebum levels.
Semi-solid Ice Packs	Local Commercial Source	N/A	Applied for precisely 15 minutes immediately post-treatment for epidermal cooling.
Skin Analysis System Main Unit	Courage + Khazaka Electronic GmbH, Cologne, Germany	Multi Probe Adapter (MPA 9)	Main delivery system anchoring the biophysical probes.
Statistical Software	IBM, Armonk, NY, USA	SPSS Statistics 26.0 (RRID: SCR_002865)	Used for all two-tailed parametric and non-parametric statistical analyses.
Thermography Device	FLIR Systems, Wilsonville, OR, USA	FLIR E4	Handheld infrared thermography device used to monitor skin temperature (15–33 °C) during immediate post-treatment ice pack application.
VISIA Imaging System	Canfield Scientific, Parsippany, NJ, USA	VISIA 7	Standardized multi-spectral facial complexion analysis.