Laser hair reduction works best on hair in which phase?

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

Answer: (A)

Laser hair reduction works best when the hair is in the growth phase because that’s when the hair follicle is actively processing and contains concentrated pigment near the follicle, which is what the laser targets. The energy from the laser is absorbed by melanin in the hair shaft and converts to heat, damaging the hair follicle to slow or stop future growth. In the growth (anagen) phase, the hair is firmly attached to the follicle and the pigment concentration near the follicle is highest, making the laser most effective at delivering its damaging heat to the follicle.

In other phases, the situation changes. During the transition phase, the hair follicle shrinks and the hair stops growing, with less pigment near the follicle, so absorption and damage are reduced. In the resting phase, hair isn’t actively growing and may be less pigmented or not anchored as strongly, further lowering the laser’s effectiveness. The shedding phase involves hairs that are already releasing from the follicle, so there’s little target for the laser to act on. Because hairs cycle asynchronously, multiple treatment sessions are needed to catch as many hairs as possible during their anagen phase for lasting reduction.