What is selective photothermolysis?

• A. Absorption of all light equally
• B. Selective absorption of a specific light targeted by a chromophore
• C. Targeting multiple chromophores simultaneously
• D. Mechanical disruption of tissue

Answer: (B)

Selective photothermolysis means using light that is absorbed preferentially by a specific chromophore so the energy heats and damages only that target while sparing surrounding tissue. In laser hair removal, we choose a wavelength that melanin in the hair follicle absorbs strongly, then deliver a pulse short enough that the heat stays confined to the follicle (its thermal relaxation time). This targeted heating damages the follicle without harming most of the surrounding skin. The concept hinges on matching the chromophore (the part that absorbs light) with the right wavelength and pulse duration, so other tissues absorb little and are protected. This principle can apply to other targets by selecting different chromophores and appropriate parameters. The other ideas describe non-selective absorption, targeting many chromophores at once, or mechanically disrupting tissue, which aren’t how selective photothermolysis works.