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High-Dose Ultraviolet Light Exposure Reduces Scar Hypertrophy in a Rabbit Ear Model

Background: The effects of ultraviolet light exposure on scar pigmentation are well documented. There is a commonly held belief among physicians that sun exposure may also worsen the appearance of fresh scars and result in excess collagen deposition. However, few studies have documented a relationship between ultraviolet light exposure and hypertrophic scarring. This study sought to evaluate the effect of ultraviolet light exposure on scar hypertrophy in an established rabbit model of cutaneous scarring. Methods: Four 7-mm ulcers were created on the ventral ears of eight rabbits. Starting on postoperative day 15, half of the wounds were exposed to ultraviolet-B radiation daily for either 7 or 14 days. Ultraviolet-B–exposed (n = 16) and control (n = 16) scars were harvested on postoperative day 32 for histologic and reverse-transcriptase polymerase chain reaction analysis. Results: Exposure to ultraviolet-B radiation for 7 or 14 days was associated with a 52 percent (p < 0.01) or 74 percent (p < 0.05) reduction in scar volume, respectively, compared with controls. In wounds subjected to ultraviolet-B radiation for 14 days, collagen type I-α2 mRNA expression was 29 percent lower than in controls (p < 0.05). There was no difference in the mRNA expression of transforming growth factor-β1. Conclusions: These short-term observations demonstrate that ultraviolet-B radiation exposure reduces scar hypertrophy in this clinically relevant animal model. A reduction in collagen production or increase in collagen breakdown may account for this result. However, sunscreen should still be used as primary protection when skin is exposed to direct sunlight.