Blue light LED works by killing Propionibacterium acnes, the bacteria that lives below the surface of the skin. It works to improve the presence of mild-to-moderate acne by destroying this bacteria on the face and in the pores which is responsible for causing acne.
The P. Acnes bacteria is a harmless bacteria that exists and feeds off of human skin. In some cases, however, the bacteria can spread and grow. This clogs the pores and irritates the skin, which in turn produces the inflammation and redness commonly associated with acne.
Blue light activates a specific compound in the waste products of P. Acnes, turning the waste into a toxin that, while harmless to the person, destroys the bacteria and thus the cause of the acne.