Photobiomodulation (PBM) is a green approach to maintain human health, and is often used in disease prevention or treatment. Its health enhancement, especially exercise-induced fatigue treatment with intranasal low intensity laser therapy, will be discussed. Function-specific homeostasis (FSH) is a negative-feedback response of a biosystem to maintain the function-specific conditions inside the biosystem. An individual system might be classified as FSH-essential system (FES) and FSH-non-essential system (FNS) which homeostasis can be written as FESH and FNSH for short, respectively. FSH quality might be enhanced by study or training (SOT). Extraordinary SOT disrupts the formal FSH and establishes FESH. Ordinary SOT maintains FESH and establishes FNSH and then a new FSH, and then maintains the new FSH. The cellular rehabilitation of low level laser irradiation or monochromatic light might promote the establishment of FESH, FNSH and FSH, shorten SOT period and then promote health.