IPL filters out most of the light so that only specific wavelengths of visible light are used for the treatment. The energy/heat from the light will be absorbed by different pigments inside the skin, such as melanin and haemoglobin. When the pigments are heated, the result will be a controlled damage inside the skin. Since it is only the pigment containing cells that are heated, the damage will be selective. The selective damage will trigger a healing response and rejuvenation of the skin. IPL is marketed to reduce the appearance of wrinkles, pigment spots, superficial capillaries, redness and to stimulate new collagen formation. IPL has a similar mode of action as lasers but uses light of a broader spectrum.
Reference:
Ganceviciene R. et al, Dermato endocrinol. 2012;4(3):308–319.