In 1967 a few years after the first working laser was invented, Endre Mester in Semmelweis University in Budapest, Hungary wanted to find out if laser might cause cancer. He took some mice, shaved the hair off their backs, divided them into two groups and gave a laser treatment with a low powered ruby laser to one group. They did not get cancer and to his surprise the hair on the treated group grew back more quickly than the untreated group. That was how “laser biostimulation” was discovered (Effect of Laser on Hair Growth of Mice. Mester, E. Szende, B. and Tota, J.G. (1967). Kiseri Orvostud 19. 628-631).
Photobiomodulation (PBM) also known as low-level laser (or light) therapy (LLLT or LILT), has been known for almost 50 years but still has not gained widespread acceptance in the United States due to its more recent implementation into this country (it was FDA approved in 2003). However, in recent years, much knowledge has been gained about the molecular, cellular, and tissular mechanisms of action.
In more common terms: Light therapy or Laser therapy works at a cellular level. The photons of light penetrate into the tissues and stimulate a cascade of effects that lead to tissue healing. This includes an increased production of ATP in the mitochondria and increased DNA synthesis both of which lead to increased production of new healthy collagen fibers and proteins. Muscles are formed of protein filaments called actin and myosin. Collagen is the main component of connective tissues (tendons and ligaments) and is also abundant in cartilage, bones and discs. Therefore light therapy helps form new healthy tissue in an injured area. It also stimulates increased white blood cell formation, including a portion of our white blood cells called macrophages. Macrophages are a bit like little “Pac-men” in that their job is to clean up scar tissue and debris. So the light therapy also helps in the reduction of scar tissue in an injured area.
For the science geeks: “One of the most important chromophores is cytochrome c oxidase (unit IV in the mitochondrial respiratory chain), which contains both heme and copper centers and absorbs light into the near-infra-red region. The leading hypothesis is that the photons dissociate inhibitory nitric oxide from the enzyme, leading to an increase in electron transport, mitochondrial membrane potential and ATP production. Another hypothesis concerns light-sensitive light-sensitive ion channels that can be activated allowing calcium to enter the cell. After the initial photon absorption events, numerous signaling pathways are activated via reactive oxygen species, cyclic AMP, NO and Ca2+, leading to activation of transcription factors. These transcription factors can lead to increased expression of genes related to protein synthesis, cell migration and proliferation, anti-inflammatory signaling, anti-apoptotic proteins, antioxidant enzymes. Stem cells and progenitor cells appear to be particularly susceptible to LLLT (Proposed Mechanisms of Photobiomodulation or Low-Level Light Therapy, IEEE J Sel Top Quantum Electron, 2016 May-Jun; 22 (3), de Freitas LF, Mablin MR).