I don't know that much about it. But I do know that it was the only thing that helped my cousin. A quick Google search says: (Of course check w/ HV on this as I'm not even close to being an expert.)
"Infrared light activates ATP (adenosine triphosphate) in the skin cells. ATP is the main energy source for cellular function. This sets in motion the body's natural processes to kill the bacteria that cause Acne and to restore the skin through cell renewal.
Using a 1450-nm diode laser treatment on 19 patients, scientists reported that Acne lesions were decreased by 37 percent after one treatment, according to Jeffrey S. Dover, MD, FRCPC. After two treatments, they were reduced by 50 percent, and after three treatments lesions were reduced by 83 percent.
The study also reported that patients commonly experienced erythema and edema after treatment, but it went away in 24 hours or less. No other side effects were noted. It was unclear from the study whether the treatment worked by reducing the numbers of Propionibacterium acnes or by shrinking the sebaceous glands by thermal damage, although probably the latter. Shrinking the sebaceous glands is how the popular Acne treatment Accutane(R) works."