Evaluation of Wavelength-Dependent Hair Growth Effects on Low-Level Laser Therapy: An Experimental Animal Study

In a 2015 study, researchers evaluated the effects of low-level laser therapy (LLLT) on hair growth in 25 male Sprague-Dawley rats using wavelengths of 632, 670, 785, and 830 nm. The study found that the 830-nm wavelength was the most effective in promoting hair growth, followed by the 785-nm wavelength. The treatments were administered over a 2-week period with an energy density of 1.27 J/cm², later increased to 1.91 J/cm², on alternating days. Photographic and histological analyses confirmed the positive correlation between longer wavelengths and hair growth rate, with no significant thermal effects observed. The study suggested that hair color and type might influence LLLT effectiveness due to melanin absorption, recommending future research with diverse hair loss models and fur colors. The research was funded by the Catholic University of Daegu and adhered to ethical animal research standards.