ABSTRACT
The skin ages both from the inside, chronological or intrinsic aging, and from the outside, particularly from exposure to solar radiation causing photoaging. Photoaging works in synergy with intrinsic aging mostly through the induction of oxidative stress which accelerates the gradual natural deterioration of the structure of all components of both the epidermis and the dermis. The pool of dermal mesenchymal cells which differentiate into new, active fibroblasts is gradually depleted, and the integrity of the skin, dependent on collagen fibers for its shear strength and elastic fibers for its capability to reform after deformation, weakens, allowing both wrinkling and skin laxity. A range of interventions is available, from the noninvasive such as the regular application of moisturizing and nutritive creams to the frankly invasive such as plastic and reconstructive surgery, but neither really turns back the skin aging clock. What is required is repair of all fibrous aspects of the elastotic ECM with recruitment of “young” fibroblasts together with a healthy vascular plexus. This sounds like wound healing: in fact, it can be argued that good skin rejuvenation depends on the same proliferative and remodeling processes associated with wound healing. In the past two decades a variety of more or less invasive laser modalities has been developed deliberately to damage the aging skin and force it to repair and regenerate itself, but patient downtime is long and the potential for side effects is high. Since photodamage plays the major role in skin aging, how elegant it would be to fight the damage caused by light with a different, noninvasive form of light which could encourage skin repair from the inside out by photobiomodulating the activity of skin cells without heat and without damage: to use therapy with light, phototherapy, to turn back the skin aging clock. It is already happening, and the why, what, and how is the subject matter of this chapter.
