Abstract: Objective To study the effects of different doses of UVA1 on the development of hypertrophic scar in rabbit ears induced by excision of full-thickness skin. Methods A hypertrophic scar model was established by excision of full-thickness skin （2 cm × 5 cm） on the ventral surface of rabbit ears. A total of 18 New Zealand rabbits were randomly divided into 3 equal groups to receive UVA1 radiation on the left ears immediately, 1 month, and 2 months after the excision, respectively, and every group were classified into two subgroups to be irradiated with 60 and 110 J/cm2 of UVA1, respectively, for 30 sessions. The right ears served as control without irradiation. HE staining and Masson staining were used to examine the dermal thickness and collagen content in scar, respectively. Results Compared with pre-irradiation, the dermal thickness （t = 5.85, 4.94, respectively, both P < 0.05） and collagen content （t = 6.50, 8.02, respectively, both P < 0.05） significantly decreased in scar irradiated with UVA1 of 110 J/cm2 one and two months after the excision. The difference value in dermal thickness and collagen content at the beginning and at the end of the study significantly differed between irradiated and non-irradiated ears in the rabbits treated with UVA1 of 110 J/cm2 （P < 0.05）. The effects of UVA1 on dermal thickness and collagen content were dose-dependent （P < 0.05）. On the contrary, the dermal thickness and collagen content markedly increased in scars of rabbits irradiated with UVA1 immediately after the excision （P < 0.05）. Conclusions To begin UVA1 exposure of hypertropic scar in rabbits after epithelialization may lead to the softening of scar, thinning of skin, and decrease of collagen content. However, immediate irradiation with UVA1 after wound could not prevent the development of hypertrophic scar in rabbits, in contrast, it exacerbated the severity of scar.

Key words: scar, model, wound repair, ultraviolet A1, long-wave ultraviolet, animal