Long-Lasting Muscle Thinning Induced by Infrared Irradiation Specialized With Wavelengths and Contact Cooling: A Preliminary Report

Objective: Infrared (IR) irradiation specialized with wavelengths and contact cooling increases the amount of water in the dermis to protect the subcutaneous tissues against IR damage; thus, it is applied to smooth forehead wrinkles. However, this treatment consistently induces brow ptosis. Therefore, we investigated whether IR irradiation induces muscle thinning. Methods: Rat central back tissues were irradiated with the specialized IR device. Histological evaluation was performed on sagittal slices that included skin, panniculus carnosus, and deep muscles. Results: Significant reductions in panniculus carnosus thickness were observed between controls and irradiated tissues at postirradiation day 30 (P30), P60, P90, and P180; however, no reduction was observed in nonirradiated controls from days 0 to 180. No significant changes were observed in the trunk muscle over time. From day 0, dermal thickness was significantly reduced at P90 and P180; however, no difference was observed between P180 and nonirradiated controls at day 180. DNA degradation consistent with apoptosis was detected in the panniculus carnosus at P7 and P30. Conclusions: We found that IR irradiation induced long-lasting superficial muscle thinning, probably by a kind of apoptosis. The panniculus carnosus is equivalent to the superficial facial muscles of humans; thus, the changes observed here reflected those in the frontalis muscle that resulted in brow ptosis. The IR device used in this study simulated solar IR radiation that reaches the skin. Therefore, exposure to solar IR radiation may cause thinning of the superficial facial muscles. This should be prevented with sunscreen that protects against IR radiation.