Which of the following is not a chromophore listed for LHR?

• A. Melanin
• B. Water
• C. Keratin
• D. Blood

Answer: (C)

Laser hair removal works through selective photothermolysis: energy must be absorbed by a chromophore in the hair follicle so heat is generated there rather than in surrounding tissue. The chromophores relevant to LHR are melanin in the hair, water in tissue, and hemoglobin in blood. Keratin, while a major structural component of hair, does not absorb the common LHR wavelengths sufficiently to serve as a practical target. Because keratin doesn’t meaningfully absorb the laser light, it won’t convert the energy into heat to damage the follicle, which is why it’s not used as a chromophore for LHR. The other three can contribute to how energy is deposited in tissue, especially melanin in dark hair, but keratin does not play that role.