Jelena Barbaric, Rachel Abbott, Pawel Posadzki, Mate Car, Laura H Gunn, Alison M Layton, Azeem Majeed, Josip Car

Acne vulgaris is a very common skin problem that presents with blackheads, whiteheads, and inflamed spots. It frequently results in physical scarring and may cause psychological distress. The use of oral and topical treatments can be limited in some people due to ineffectiveness, inconvenience, poor tolerability or side-effects. Some studies have suggested promising results for light therapies. To explore the effects of light treatment of different wavelengths for acne. We searched the following databases up to September 2015: the Cochrane Skin Specialised Register, CENTRAL, MEDLINE, Embase and LILACS. We searched ISI Web of Science and Dissertation Abstracts International (from inception). We also searched five trials registers, and grey literature sources. We checked the reference lists of studies and reviews and consulted study authors and other experts in the field to identify further references to relevant randomised controlled trials (RCTs). We updated these searches in July 2016 but these results have not yet been incorporated into the review. We included RCTs of light for treatment of acne vulgaris, regardless of language or publication status. We used standard methodological procedures expected by Cochrane. We included 71 studies, randomising a total of 4211 participants.Most studies were small (median 31 participants) and included participants with mild to moderate acne of both sexes and with a mean age of 20 to 30 years. Light interventions differed greatly in wavelength, dose, active substances used in photodynamic therapy (PDT), and comparator interventions (most commonly no treatment, placebo, another light intervention, or various topical treatments). Numbers of light sessions varied from one to 112 (most commonly two to four). Frequency of application varied from twice daily to once monthly.Selection and performance bias were unclear in the majority of studies. Detection bias was unclear for participant-assessed outcomes and low for investigator-assessed outcomes in the majority of studies. Attrition and reporting bias were low in over half of the studies and unclear or high in the rest. Two thirds of studies were industry-sponsored; study authors either reported conflict of interest, or such information was not declared, so we judged the risk of bias as unclear.Comparisons of most interventions for our first primary outcome 'Participant's global assessment of improvement' were not possible due to the variation in the interventions and the way the studies' outcomes were measured. We did not combine the effect estimates but rated the quality of the evidence as very low for the comparison of light therapies, including PDT to placebo, no treatment, topical treatment or other comparators for this outcome. One study which included 266 participants with moderate to severe acne showed little or no difference in effectiveness for this outcome between 20% aminolevulinic acid (ALA)-PDT (activated by blue light) versus vehicle plus blue light (risk ratio (RR) 0.87, 95% confidence interval (CI) 0.72 to 1.04, low-quality evidence). A study (n = 180) of a comparison of ALA-PDT (activated by red light) concentrations showed 20% ALA was no more effective than 15% (RR 1.05, 95% CI 0.96 to 1.15) but better than 10% ALA (RR 1.22, 95% CI 1.05 to 1.42) and 5% ALA (RR 1.47, 95% CI 1.19 to 1.81). The number needed to treat for an additional beneficial outcome (NNTB) was 6 (95% CI 3 to 19) and 4 (95% CI 2 to 6) for the comparison of 20% ALA with 10% and 5% ALA, respectively.For our second primary outcome 'Investigator-assessed changes in lesion counts', we combined three RCTs, with 360 participants with moderate to severe acne and found methyl aminolevulinate (MAL) PDT (activated by red light) was no different to placebo cream plus red light with regard to change in inflamed lesions (ILs) (mean difference (MD) -2.85, 95% CI -7.51 to 1.81), percentage change in ILs (MD -10.09, 95% CI -20.25 to 0.06), change in non-inflamed lesions (NILs) (MD -2.01, 95% CI -7.07 to 3.05), or in percentage change in NILs (MD -8.09, 95% CI -21.51 to 5.32). We assessed the evidence as moderate quality for these outcomes meaning that there is little or no clinical difference between these two interventions for lesion counts.Studies comparing the effects of other interventions were inconsistent or had small samples and high risk of bias. We performed only narrative synthesis for the results of the remaining trials, due to great variation in many aspects of the studies, poor reporting, and failure to obtain necessary data. Several studies compared yellow light to placebo or no treatment, infrared light to no treatment, gold microparticle suspension to vehicle, and clindamycin/benzoyl peroxide combined with pulsed dye laser to clindamycin/benzoyl peroxide alone. There were also several other studies comparing MAL-PDT to light-only treatment, to adapalene and in combination with long-pulsed dye laser to long-pulsed dye laser alone. None of these showed any clinically significant effects.Our third primary outcome was 'Investigator-assessed severe adverse effects'. Most studies reported adverse effects, but not adequately with scarring reported as absent, and blistering reported only in studies on intense pulsed light, infrared light and photodynamic therapies. We rated the quality of the evidence as very low, meaning we were uncertain of the adverse effects of the light therapies.Although our primary endpoint was long-term outcomes, less than half of the studies performed assessments later than eight weeks after final treatment. Only a few studies assessed outcomes at more than three months after final treatment, and longer-term assessments are mostly not covered in this review. High-quality evidence on the use of light therapies for people with acne is lacking. There is low certainty of the usefulness of MAL-PDT (red light) or ALA-PDT (blue light) as standard therapies for people with moderate to severe acne.Carefully planned studies, using standardised outcome measures, comparing the effectiveness of common acne treatments with light therapies would be welcomed, together with adherence to the Consolidated Standards of Reporting Trials (CONSORT) guidelines.