Traditionally, lasers have been utilized in many aspects of medicine, such as surgery, cancer treatment, and cosmetic applications. The laser irradiation that was commonly used in cosmetic surgery or cancer therapy is high intensity laser irradiation which can cut through the human bodies and burn the tissues. Except this well-known high intensity laser therapy, there is another type of laser therapy, photobiomodulation (PBM), in which a low level/intensity/power laser irradiation or monochromatic light is used to modulate biological functions without irreversible damage. It has been widely used to reduce pain and inflammation, accelerate wound healing and hair growth, prevent cell death and tissue damage, and improve blood circulation since the invention of lasers in the 1960s. Currently, PBM is not only used to treat diseases, but also used to promote health.

Despite many laboratory experiments and clinical trials, the cellular and molecular mechanisms of PBM continue to be elusive. In this special edition, we present peer-reviewed up-to-date studies which focused on the mechanisms of PBM and its clinical applications.

The original research articles covered many aspects of PBM, from basic biomedical research to clinic applications, from in vitro cell-based studies to in vivo human tissues. In the two review papers, the authors proposed an interesting theory of PBM based on the function-specific homeostasis, which is a negative feedback response for a function to be perfectly performed. Besides the studies on PBM, we also selected several papers on photodynamic therapy and laser surgery in the current issue.

We highly appreciate the quality, originality, and novelty of the studies submitted to this special issue, and we welcome the proposal of the journal to publish a second special issue dedicated to the field of PBM in the near future.

Timon Cheng-Yi Liu
Rui Duan
Lutz Wilden