Light therapy attempts to help prevent papules and pustules, the everyday "zits" that many people get that are inflamed and red. Smaller acne lesions such as non-inflamed whiteheads and blackheads, as well as severe acne lesions such as cysts and nodules tend to respond more poorly. Light therapy, usually administered with at-home devices is normally performed twice per day, and uses blue and sometimes blue + red light. When blue light reaches the sebaceous (oil) glands in the skin, it can help excite porphyrins, which are compounds inside acne bacteria.1-2 When activated by light, these porphyrins kill the bacteria from the inside out.3 Red light, while it is less researched, may help reduce inflammation and improve healing.4 Certain light spectrums may also inhibit sebum (skin oil) production and lessen inflammation. Exactly how light therapy exerts its effects is still not understood.5 Tabletop light therapy devices normally require 10-15 minutes of treatment, with the user sitting very close to the device. Handheld devices, which some experts claim help with light penetration, require a person to hold the device directly on several areas of his/her face and requires a total of 30 minutes to 1 hour of treatment time twice per day.6 Goggles are required with both types of devices since blue light can harm the retina. People can normally use light therapy in conjunction with other acne therapies, with the exception of isotretinoin (Accutane).
We do not have enough data at this time to make conclusive statements about how well light therapy works. Studies have generally been small and results tend to vary widely, from "statistically insignificant" clearance7 all the way up to 81% clearance8 of acne. Current literature points toward blue + red light showing slightly better results than blue alone at this time. Emerging research is pointing toward at best moderate and temporary improvement of acne. According to a meta-analysis published by the British Journal of Dermatology in 2009, "our review found only limited or no benefit is given by light therapies alone."9
At-home light therapy machines usually have very few side effects, which include slight irritation or redness only in very sensitive individuals. The level of UV light in these devices is also very low and appears to be well within the range of safety.
Using light therapy requires much patience. Devices cost from $150-$350, and results are normally moderate at best. While light devices may help kill some acne bacteria, benzoyl peroxide, when used in adequate dosages, kills acne bacteria almost entirely, and does so without much of the complications to one's daily schedule.