Effects of near-infrared photobiomodulation on local skin blood flow in healthy subjects

Photobiomodulation causes an immediate increase in local blood flow. This study aimed to investigate the effect of 890 nm NIR exposure on local skin blood flow in young and middle-aged healthy subjects. In this placebo-controlled clinical trial, 12 young and 12 middle-aged healthy subjects received either continuous or intermittent NIR exposure (890 nm, 5.1 mW /cm 2 , 4.6 J/cm 2 , and 35.9 J total energy) on the skin of the upper lateral arm. The continuous exposure experiment, used in young subjects only, applied 30 minutes of continuous NIR light (experiment 1). The intermittent exposure experiment, used in both age groups, applied NIR light through 10 cycles of 3 minutes NIR exposure and 2 minutes OFF (for recording blood flow), resulting in 50 minutes of total time. Laser Doppler flowmetry and thermal images were used to monitor local blood flow and skin temperature. In young subjects, continuous NIR exposure compared to placebo significantly increased blood flow for the first 20 minutes post-exposure. Further, in young and middle-aged subjects, intermittent exposure increased blood flow during the whole exposure period and 15 minutes post-exposure. In young subjects, blood flow after continuous NIR exposure was significantly higher than intermittent NIR exposure only for the first 10 minutes. For intermittent exposure comparison between the two age groups, the blood flow was significantly higher in middle-aged subjects. We conclude that NIR PBM increases local skin blood flow in young and middle-aged subjects. The mode of NIR irradiation and the subjects’ age influenced the local skin blood flow response.