Photobiomodulation effects on keratinocytes cultured in vitro: a critical review

Photobiomodulation therapy (PBMT) has been widely used for the promotion of tissue repair. Despite these therapeutic benefits, in some cases, PBMT appears to be unsuccessful, and the strongest hypothesis is that this failure is due to inadequate light dosimetry and wavelengths. The objective of the present critical review was to evaluate the effects of PBMT on cultured keratinocytes using blue, red, or near-infrared light categorized into arbitrary ranges of energy density (0.1-5.0, 5.1-10.0, 10.1-15.0, and over 15.0 J/cm²). The electronic searches were conducted in PubMed, Web of Science, Scopus and LILACS databases, and included LASER or LED devices. A total of 55 articles evaluating the effects of PBMT on cell viability, proliferation, migration, and cytokine and growth factor production were included. Overall, the studies failed to provide detailed information about light dosimetry or detailed experimental conditions. The vast majority of the energy densities tested produced unmodified results regardless of the wavelength applied. However, it was possible to observe that red and near-infrared light had more stimulatory effects than blue light. In addition, for all parameters analyzed, favorable outcomes were mostly obtained in the range of 0.1-5.0 J/cm². The less explored energy densities were within the 10.1-15.0 J/cm² range. Energy densities above 15.0 J/cm² were ineffective or tended to cause cell death. The heterogeneity of the data does not allow us to define a PBMT range setting protocol that would have beneficial effects on keratinocytes.