Skin photorejuvenation effects of light‐emitting diodes ( LED s): a comparative study of yellow and red LED s in vitro and in vivo

Summary Background Red‐coloured light‐emitting diodes ( LED s) can improve skin photorejuvenation and regeneration by increasing cellular metabolic activity. Aim To evaluate the effectiveness of visible LED s with specific wavelengths for skin photorejuvenation in vitro and in vivo . Methods Normal human dermal fibroblasts ( HDF s) from neonatal foreskin were cultured and irradiated in vitro by LED s at different wavelengths (410–850 nm) and doses (0–10 J/cm 2 ). In vivo experiments were performed on the skin of hairless mice. Expression of collagen ( COL ) and matrix metalloproteinases ( MMP s) was evaluated by semi‐quantitative reverse transcription PCR (semi‐ qRT ‐ PCR ), western blotting and a procollagen type I C‐peptide enzyme immunoassay ( EIA ). Haematoxylin and eosin and Masson trichrome stains were performed to evaluate histological changes. Results In HDF s, COL I was upregulated and MMP ‐1 was downregulated in response to LED irradiation at 595 ± 2 and 630 ± 8 nm. In the EIA , a peak result was achieved at a dose of 5 J/cm 2 with LED at 595 ± 2 nm. In vivo , COL I synthesis was upregulated in a dose‐dependent manner to both 595 and 630 nm LED irradiation, and this effect was prolonged to 21 days after a single irradiation with a dose of 100 J/cm 2 . These histological changes were consistent with the results of semi‐ qRT ‐ PCR and western blots. Conclusion Specific LED treatment with 595 ± 2 and 630 ± 8 nm irradiation was able to modulate COL and MMP s in skin, with the effects persisting for at least 21 days after irradiation. These findings suggest that yellow and red LED s might be useful tools for skin photorejuvenation.