What chromophore do most hair-removal lasers target, and why is it selective for hair follicles?

• A. Melanin in the hair pigment
• B. Water in skin tissue
• C. Hemoglobin in blood
• D. Keratin in hair shaft

Answer: (A)

The key idea is selective photothermolysis: lasers damage the hair follicle by delivering energy that is strongly absorbed by the hair’s pigment, causing enough heat to disable growth while sparing most surrounding skin. The chromophore here is melanin in the hair pigment, which concentrates energy absorption in the follicle during the growth phase when the hair is most pigmented. Because the surrounding skin contains far less melanin, the laser energy stays focused on the hair follicle, providing selective heating and minimizing skin damage. Other substances like water in skin tissue, hemoglobin in blood, or keratin in the hair shaft don’t absorb these laser wavelengths as effectively to produce the same selective follicle targeting.