Light-based therapies have been proven to influence and perhaps reverse skin ageing at clinical, molecular and histologic levels. Laser technology decreases photodamage by promoting collagen type I and III synthesis and enhancing the expression of heat shock protein. : This study aims to assess different doses of 675 nm irradiation on human dermal fibroblast cells to evaluate the potential therapeutic effects on the rejuvenation process. This study employed a laser system that emits 675 nm wavelength: 260, 390, 520 and 650 J/cm doses were tested on adult human dermal fibroblast cells. Cellular viability, proliferation, and synthesis of type I and III collagen were studied. No dose tested showed effects on cell viability and proliferation at 24 and 48 h from the irradiation. Doses of 260 and 520 J/cm causes a significant decrease in type I collagen fluorescence intensity, while 390 J/cm elicits a significant increase in type III collagen expression. Our results showed that 675 nm laser irradiation does not affect cell viability while modulating cell proliferation and collagen synthesis in human adult cultured fibroblasts in vitro. These findings suggest that 675 nm laser irradiation potentially plays a role in skin rejuvenation.