Influence of the Anagen : Telogen ratio on Q-switched Nd : YAG laser hair removal efficacy

Background and Objective: Laser hair removal is believed to affect only ana gen hairs. However, proof of this belief in humans is lacking. The objectiv e of this study was to determine the influence of the anagen: telogen ratio on the results of Q-switched Nd:YAG laser hair removal. Study Design/Materials and Methods: Fifteen subjects had four test sites delineat ed in one body area. The test sites were chosen by trimming the hair and ev aluating the area in 2 weeks. At that time, the anagen hairs were at least twice as long as the nongrowing telogen hairs and, therefore, could be diff erentiated and counted. Two sites with a low anagen number and two with a h igh number were chosen for comparison. All sites were then treated with a Q -switched Nd:YAG laser. Follow-up examination was in 1 month. Results: Test sites with a low anagen number demonstrated a low level of ha ir loss compared with those sites with a high anagen number. A significantl y higher percentage of hair loss was noted when comparing the anagen-only w ith total hair loss. In addition, lasing plus shaving demonstrated more hai r loss than lasing alone. These findings indicated that anagen hairs were c learly affected, but the immediate clinical effect on telogen hairs was min imal. Conclusion: Q-switched Nd:YAG laser treatment of anagen hairs results in a rapid switch to telogen and a subsequent clinically obvious shedding of the hair shaft. This process causes a greater percentage hair loss at sites wi th high anagen number. Telogen hairs demonstrate no such effect and remain in their pretreatment phase after lasing. (C) 2000 Wiley-Liss, Inc.