Many lasers have claimed the clinical efficacy on skin rejuvenation. Generally, there are two main laser effects consistent with clinical applications. Systematic and comparative studies are needed to compare different laser effects and probe into the mechanism of laser skin rejuvenation. To conduct a comparative study of collagen remodeling with two different laser effects on mice model in vivo. After depilation, the back skin of KM mice was used for the study. The 1064 nm Q-switched (5 ns) and long-pulsed (0.3 ms) Nd:YAG lasers were applied based on optimal tissue reaction fluence test to irradiate one side of the mice back and leave the other side as the control. Then the collagen remodelling were evaluated at 0, 1, 7, 21, 30 and 60 days, with biophysical parameters' measurements, histological and biochemical examination.

The two lasers applied showed statistical improvements in skin elasticity, dermal thickness and synthesis of hydroxyproline compared with their own controls. Between the two lasers, the Q-switched 1064-nm laser resulted in greater improvements than that of the long-pulsed 1064-nm laser after two months of resultss. Collagen type III increased markedly after the Q-switched 1064-nm laser results whereas more collagen type I was elicited by the long-pulsed 1064-nm laser. Q-switched 1064-nm laser was more effective in collagen remodeling compared with long-pulsed 1064-nm laser. Photo-mechanic reaction can cause more synthesis of collagen type III whereas the photo-thermal effect is in favor of formation of collagen type I.