sentences:  Once the light activates the sensitizing substance, this generates free radicals and reactive oxygen species in the skin, which purposefully damage the sebaceous glands and kill "C. acnes" bacteria.Many different types of nonablative lasers (i.e., lasers that do not vaporize the top layer of the skin but rather induce a physiologic response in the skin from the light) have been used to treat acne, including those that use infrared wavelengths of light.Ablative lasers (such as CO2 and fractional types) have also been used to treat active acne and its scars.