Light-based hair reduction treatments are effective only when hair is in which growth stage?

• A. Anagen
• B. Catagen
• C. Telogen
• D. Exogen

Answer: (A)

Light-based hair reduction is most effective when hair is actively growing, in the anagen phase. During anagen, the hair is firmly anchored in the follicle and contains melanin near the root, which is what the light energy targets. The absorbed energy heats and damages the hair follicle’s growth cells, reducing future growth. In the other phases—catagen (transition), telogen (resting), and exogen (shedding)—the hair is not actively growing or the pigment is less available near the follicle, so the energy has less to absorb and the treatment is far less effective. A series of sessions timed to catch hairs as they enter anagen yields the best overall results.