Remodeling of dermal collagen in photoaged skin using low‐dose 5‐aminolevulinic acid photodynamic therapy occurs via the transforming growth factor‐β pathway

5‐Aminolevulinic acid photodynamic therapy (ALA‐PDT) is known to be effective in the treatment of photoaged skin. However, the molecular mechanisms still remain elusive. Protoporphyrin IX (PpIX) fluorescence is primarily located in the epidermis while ALA‐PDT affects the dermal collagen, presumably by an indirect mechanism. This study aimed to investigate the molecular communication in low‐dose ALA‐PDT occurring between epidermal keratinocytes...