The diagram below shows a cross section of a typical example of acne.

Acne occurs when tiny oil glands in the skin are over active, typically dead skin cells block the top of the skin pore and the oil builds up. The blocked pore becomes the perfect breeding environment for bacteria and the pore becomes infected and inflamed.

IPL light targets the acne (the heat generated by the light in this case not only degrades the oil gland but also destroys the bacteria). A typical filter used would be a broad filter of 420 nm – 1200 nm.
Acne Removal Principle with IPL - High Profile Technologies Ltd