Which of the following methods is an example of permanent hair reduction?

Light-based hair removal methods, such as laser hair removal or intense pulsed light (IPL), are designed to reduce hair regrowth over time by targeting the hair follicles. These methods use specific wavelengths of light that are absorbed by the pigment in the hair, which subsequently damages the follicle and inhibits future hair growth. As a result, these techniques can lead to significant and lasting reduction in hair density and growth, qualifying them as examples of permanent hair reduction.

In contrast, the other methods—shaving, sugaring, and threading—are all temporary hair removal techniques. Shaving cuts hair at the surface of the skin and does not affect the follicle itself, leading to regrowth in a short period. Sugaring and threading also remove hair from the follicle but do not provide any long-term effects on hair growth. They typically lead to regrowth within a few weeks. Therefore, the only method listed that offers the potential for permanent hair reduction is the light-based approach.