Wound healing comprises of sequential changes in different cell initiation, activation and migration events. Those changes are categorized into different, yet overlapping, phases: (1) hemostasis; (2) inflammatory; (3) proliferative; and (4) remodeling.48,49 This study has demonstrated the feasibility of an optical microscopy-based noninvasive approach, capable of providing insight into these sequential phases in terms of cellular activity and collagen regeneration independently. Negligible concentration of cells relative to the extra-cellular matrix (ECM) at the exposed dermal layer prohibit us from detecting significant cellular autofluorescence on the day of wound formation that can be used for statistical lifetime fitting.50 The higher metabolism observed both at the center and the edge of the wound, from the first to third day indicates the execution of the inflammatory response by the neutrophils and monocytes sequentially to clean the wound site by phagocytise the debris, bacteria and the damage tissue.1,51,52 The initiation of granulation phase, by fibroblast and epidermal cell migration to the center of the wound, maintained the metabolism higher after the third to sixth day of wound formation and was comparable to the first three days.53,54 However, the wounded edge healed faster than the center, and the phases of healing were also of shorter duration. Previously, Stedelmann et al. found that in the first two or three days after injury, fibroblasts migrate and proliferate. Meanwhile, after a week, they are the main cells that lay down the collagen matrix in the wound site.48 Approximately a week after wounding, contraction begins in the wound, as fibroblasts had differentiated into myofibroblasts.55 When the actins in myofibroblasts contracts, the wound edges are pulled together.55 Fibroblasts lay down collagen to reinforce the wound as the myofibroblasts contract.48 The cellular metabolic rate was observed to have decreased both at the center and edge after the tenth day. This state of lower cellular activity appears at the edge earlier than at the center, as the edge heals faster than the center due to greater access to the nourishment and growth factors from the undamaged tissues. The mean lifetime () of wounded tissues was more diverse than that of the normal skin during first few days of wound healing, but it gradually becomes similar to the normal one as it heals. Observed mean lifetime change indicates that in healed tissue, the micro environmental difference within the cell was negligible in comparison to the normal skin cells. But during the first few days of wound healing the microenvironment within the cell was different in terms of viscosity, pH and temperature that reflect cellular mobility, enzymatic reactions and inflammation respectively.46 During the first three days, collagens were observed in the exposed dermis and were degraded by the metalloproteinase enzymes secreted by the migrating epidermal cells at the wound bottom. However, as time proceeds, regeneration exceeded the degradation, and a newly laid matrix of collagen was formed gradually to fill up the wound gap, which was detected by the increase in SHG signal intensity (Fig. 5). The collagen regeneration started earlier at the edge than the center, and it remained higher throughout the process owing to its direct communication with the undamaged tissues. The collagens are deposited in the wound until the gap is filled, and the wound enters into the remodeling phase, which can last from weeks to several months. The remodeling phase is a slow process, which does not require high cellular activity. During this process, the older collagens are replaced by young and stronger ones to strengthen the wound.56 Originally disorganized collagen fibers are rearranged, cross-linked, and aligned,57 which can be observed from the images of (Fig. 6). Briefly our results indicate that at the initial phase of wound healing the metabolic rate of cells was higher, which was caused by the activated cells due to inflammation and initial cell migration. At the edge wound heals faster, which was reflected by the decrease in metabolic rate than that of center and was comparable to normal skin after three days. After eight days, new skin regenerates at the center too, and the metabolic rate becomes comparable to normal skin. But as the healing completed, the regenerated new skin forms a scar mainly comprised of collagen, which is differing from the normal skin in terms of strength and physiology. Our result indicates lower cellular activity in scar tissue than that of normal skin.