Pulsed 830‐nm Laser Irradiation Modulates Aδ‐ and C‐Fiber–Mediated Pain Thresholds in Healthy Adults: A Randomized, Sham‐Controlled Trial

OBJECTIVES: To determine whether pulsed near-infrared laser irradiation differentially modulates pain thresholds mediated by Aδ- and C-fibers in humans. MATERIALS AND METHODS: In this randomized, sham-controlled, single-blind, parallel-group trial, healthy adults received pulsed 830-nm laser irradiation (peak power 10 W) or sham irradiation applied to the volar forearm. Aδ- and C-fiber-mediated pain thresholds were assessed before and immediately after irradiation using intra-epidermal electrical stimulation delivered via a concentric bipolar electrode. Linear mixed-effects models were used to examine group × time interactions for each fiber types. RESULTS: Significant group-by-time interactions were observed for Aδ-mediated thresholds (p = 0.034) and C-fiber-mediated thresholds (p = 0.046), indicating differential pre-post changes between the laser and sham groups. Pain thresholds increased following active irradiation in both fiber types, whereas minimal changes were observed after sham irradiation. Between-group differences in change scores were associated with moderate standardized effect sizes. CONCLUSION: Pulsed 830-nm laser irradiation induces immediate modulation of peripheral nociceptive processing in humans across Aδ- and C-fibers, supporting fiber-specific modulation of nociceptive processing under controlled experimental conditions. CLINICAL TRIAL REGISTRATION: University Hospital Medical Information Network Clinical Trials Registry (UMIN-CTR), UMIN000056285.