IPL (Intense Pulsed Light) hair removal devices achieve hair removal effects through a principle known as Selective Photothermolysis. The specific principles are as follows:

1. The role of light energy
IPL devices emit a broad-spectrum intense pulsed light, typically within the wavelength range of 600-1200nm. These light energies are selectively absorbed by melanin in the skin (mainly present in hair follicles).

2. Conversion to thermal energy
The light energy absorbed by melanin is converted into thermal energy, rapidly increasing the temperature of the hair follicle, destroying the hair follicle cells and dermal papillae (structures responsible for hair growth) within the hair follicle, thereby inhibiting hair regrowth.

3. Protection of surrounding tissue
Since the IPL light waves are specially filtered and combined with the cooling system in the device (such as the Sapphire Cooling System), they only act on the melanin in the hair follicle, causing minimal harm to the surrounding skin tissue, ensuring safety and comfort during use.

4. Effectiveness on anagen hair
IPL is mainly effective on the anagen phase of hair growth because at this time, the melanin content in the hair follicle is the highest, and the absorption of light energy is the strongest. When other hairs are in the catagen or telogen phase, the effect will be reduced, thus multiple treatments are needed to cover different hair growth cycles.

In summary, IPL hair removal devices emit intense pulsed light, utilize the selective absorption of light energy by melanin, convert light energy into thermal energy, and destroy hair follicles to achieve hair removal effects. The destroyed hair follicle cells and dermal papillae will be naturally absorbed and metabolized by the body and expelled.