Background and Objectives: The use of the long-pulsed 755-nm alexandrite laser has been an effective tool in hair removal. A dynamic cooling device (DCD) is commonly used with this laser in order to minimize epidermal damage. No studies have examined how fine changes in DCD duration may affect comfort and epidermal damage during laser hair removal. This study was designed to determine what effect, changes in the duration of dynamic cooling would have on pain and epidermal damage with laser hair removal (755 nm alexandrite) in patients with darker skin types. Study Design/Materials and Methods: Ten volunteers with Fitzpatrick skin types III-V were enrolled. A 755-nm alexandrite laser with a pulse duration of 3 milliseconds and equipped with a DCD was used with the 12 mm spot size on matched treatment sites. We compared cryogen spurt durations of 0, 20, 40, 60, 80, and 100 milliseconds on pain and epidermal changes. The spray delay was set at 1 millisecond. Pain rating scales and epidermal changes (skin sloughing, hyperpigmentation, hypopigmentation and scarring) were assessed. Results: Overall a decrease in pain was seen with increases in spurt duration. A spurt duration of 20 milliseconds was beneficial for pain reduction in all patients. Longer spurt durations were associated with additional pain relief especially when geographic spacing of pulses was maximized to prevent thermal build-up. In regards to epidermal protection, most patients benefited with shorter cryogen durations of 20-60 milliseconds. There was little advantage with longer spurt durations. Some patients treated at higher fluences without cooling had no detectable side effects. Conclusions: Increasing DCD spurt duration in laser hair removal provides its strongest benefit in the area of pain reduction, particularly in type V patients. Increasing cryogen spurt durations above a protective threshold shows no significant benefit in terms of epidermal protection. Changing the spurt duration may not be as important in some patients with darker skin types.
