Michael Hamblin, PhD, Harvard's Wellman Center for Photomedicine; internationally recognized photomedicine expert and company's chief phototherapy advisor
How does low level laser light re-grow hair and is it safe? 
"Low level laser therapy (LLLT) has been shown in thousands of peer-reviewed publications to increase cellular survival, proliferation and function. The light is absorbed by mitochondria and increases cellular respiration, and induces activation of transcription factors via reactive oxygen species. Controlled clinical trials have shown efficacy in treating stroke, stimulating wound healing, orthopedic conditions and relief of chronic inflammation. Preclinical studies have shown effectiveness in spinal cord injuries, peripheral nerve regeneration, heart attacks, degenerative brain diseases and traumatic brain injury. 

Not surprisingly LLLT is able to stimulate and preserve hair follicles in patients with androgenetic alopecia and other hair loss disorders. A peer-reviewed study published in 2009 led to FDA clearance of a laser comb device for hair re-growth. The hair follicles cannot be "brought back from the dead" but significant improvement in hair density and quality can be achieved if treatment is started before hair loss has progressed too much. Preclinical studies using LLLT to stimulate ex vivo human follicles in culture and accelerate mouse hair re-growth have also been reported. 

Michael Hamblin, PhD, Harvard's Wellman Center for Photomedicine; internationally recognized photomedicine expert and company's chief phototherapy advisor
Red light at 650-nm penetrates in tissue when applied to the head as follows. Approximately 10% will penetrate the skin and perhaps 1% will penetrate through the skull. The only known side-effect of 650-nm light to living tissue is heating. A surface irradiance of more than 200 mW/cm2 is needed to produce
significant tissue heating and many times more would be needed to produce burns to the skin. The skin is efficiently cooled by blood circulation through the dermal plexus of capillaries. The sensation of warmth produced by the lasercap is due to heat produced by the laser diodes not by optical energy absorption in tissue. There is a steady state of heat transfer rapidly established so long exposure times do not lead to heat build-up. No known or hypothesized side-effects (such as carcinogenesis) of 650-nm light at the energy levels proposed to the brain or other distant organs exist.