The application of ultra-weak photon emission in dermatology

• The pros and cons of UPE as a non-invasive tool to study oxidative stress in human skin in vivo are discussed.
• The in vivo spontaneous and UVA induced UPE in skin may help us better understand how skin reacts to external challenges.
• UPE can assist the development of new treatment in skin including topical antioxidants and sunscreens.

Ultra-weak photo emission (UPE) is a phenomenon closely associated with life and provides us a rare window to look into oxidative reactions in life directly without the aid of other agents. Dozens of independent studies have investigated UPE in skin in the last 2 decades. Skin serves as a convenient target for the application of UPE. As the outmost layer of our body, skin is also subjected to the influences from environmental factors such as ultraviolet light. Therefore UPE measurement can help us better understand the interaction between skin and the outside world.A variety of dermatological interventions may benefit from UPE studies. In particular, those treatments aiming to manage the oxidative status of the skin can be monitored directly by UPE measurements. In recent years, UPE has already been used as a valuable in vivo tool to assist the selection of better skin care ingredients and products. The knowledge gained by UPE studies of skin may also help generate new insights and new targets for future treatments.This review emphasizes in vivo and clinical measurement of UPE in skin. The applications of UPE in skin research related to antioxidants and sunscreens are discussed.