Study	Reason for exclusion
Abdel 2015	It was reported that "All participants underwent facial chemical peeling: 25% TCA on the right half of their face and 30% salicylic acid on the left half every 2 weeks for 2 months." The whole randomisation remains doubtful: individuals were not randomised because all persons received the same treatment. The side of the face was not randomised because all persons received the test intervention on the right side and the control intervention on the left side. Finally, there was no obvious and no described randomisation.
Anonymous 1996	This report was not a RCT (summary review).
Barak‐Shinar 2017	Comparison is salicylic acid + botanicals plus soap versus soap. Botanicals are only given in the treatment group; hence, we cannot determine the efficacy of salicylic acid in the comparison.
Barkovic 2012	The study was published as an abstract. No randomisation was reported or implied. The study author could not be contacted to obtain clarification.
Bissonnette 2009	The type of intervention (lipo hydroxy acid) was ineligible for inclusion.
Breno 2002	The type of intervention (lipo hydroxy acid) was not eligible for inclusion.
Capitanio 2012	The type of interventions was not eligible for inclusion (zinc‐oligosaccharide versus vehicle control).
Chantalat 2006a	No randomisation was reported or implied and the study author could not be contacted to obtain clarification.
Chassard 2006	This was a pharmacokinetic study.
Chu 1997	The type of interventions was not eligible for inclusion.
Cochran 1985	The study author could not be contacted and we were unable to obtain clarification. No wording that might connected to a RCT could be found (no randomisation, no concealment, no "accidental" assignment, no generation of randomisation numbers, no central management of allocation).
Coret 2006	The study author could not be contacted and we were unable to obtain clarification. No randomisation was reported or implied.
Cotterill 1980	This report was not a clinical trial (summary review).
Cunliffe 1992	This report was not a RCT (summary review).
Danto 1966	The type of interventions were not eligible for inclusion (5% sulfur‐10% benzoyl versus 5% sulphur) and sulphur was the concomitant topical medications for acne vulgaris.
De Bersaques 1972	The type of interventions (topical vitamin A acid) was not eligible for inclusion.
Dos 2003	The study author could not be contacted and we were unable to obtain clarification. No wording that might connected to a RCT could be found (no randomisation, no concealment, no "accidental" assignment, no generation of randomisation numbers, no central management of allocation).
Draelos 2006	There were two studies in this report (Japanese and USA study) and the participants in the two studies were healthy subjects.
Elstein 1981	The type of intervention (sulfurated lime) was ineligible for inclusion.
Fang 2001	Not a RCT
Fu 2003	The type of intervention (lipohydroxyacid) was ineligible for inclusion.
Gebicki 2003	The type of intervention (1‐methylnicotinamide) was ineligible for inclusion.
Gollnick 1989	This report was published as a summary review.
Gollnick 1997	This was a non‐systematic review (this report was published in German and Frank Peinemann provided the information).
Green 2013	The type of interventions (MaxClarity, Proactiv, Murad) were not eligible for inclusion.
Gupta 2004	This report was published as a review.
Habbema 1989	The type of interventions was not eligible for inclusion.
Hjorth 1989	The report published two studies. The type of comparisons in the two studies were not eligible for inclusion (20% azelaic acid cream versus oral tetracycline).
Khodaeinai 2014	The type of interventions was not eligible for inclusion (10% azelaic acid gel with hydro‐alcoholic base versus alcohol‐free base).
Kirton 1967	The study design was not eligible for inclusion (non‐randomised).
Kreysel 1967	The type of interventions (aknichthol versus aknichthol dexa) were not eligible for inclusion. (This report was published in German and Frank Peinemann provided the information).
Lee 2003	The study design was not eligible for inclusion (not RCT).
Leyden 1997	The participants were not eligible for inclusion (healthy subjects).
Linss 1981	The type of interventions (oral medications) were not eligible for inclusion. (This report was published in German and Frank Peinemann provided the information).
MacDonald 1976	The type of intervention (actinac) was not eligible for inclusion.
Miller 2005	The study was published as an abstract. No randomisation was reported or implied and the study author could not be contacted.
NCT00848744	The trial compared formulations from the same treatment.
Norris 1987	This study was published as a summary of a poster. No randomisation was reported or implied and the study author could not be contacted.
Pastuszka 2012	This paper was published as a review.
Pereira 1994	The study was not described as randomised. All included patients received the same treatment/intervention: salicylic acid and sulphur lotion for topical use. (This study was published in Portuguese and Carolina Freitas provided the information).
Pierard‐Franchimont 1995	The participants were not eligible for inclusion (healthy subjects).
Plewig 1969	The type of interventions (vitamin A acid versus sulphur‐resorcinol versus benzoyl peroxide) were not eligible for inclusion.
Rougier 2002	The type of intervention (lipohydroxyacid) was ineligible for inclusion.
Sardesai 2003	The study author could not be contacted and we were unable to obtain clarification. No wording that might connect to a RCT could be found (no randomisation, no concealment, no "accidental" assignment, no generation of randomisation numbers, no central management of allocation).
Schachner 1990	The type of interventions were not eligible for inclusion (erythromycin‐zinc versus vehicle).
Shemer 2002	All participants received same intervention (non‐randomised).
Souza 2005	The participants were not eligible for inclusion as patients with rosacea were included.
Tarimci 1997	The study design was not eligible for inclusion (non‐randomised).
Thomas 1951	The study design was not eligible for inclusion (not RCT).
Touitou 2008	The type of interventions was not eligible for inclusion (clindamycin‐salicylic acid versus placebo).
van Steenbergen 1968	The study author could not be contacted and we were unable to obtain clarification. There was no wording reported that might be connected to a RCT. No randomisation, no concealment, no "accidental" assignment, no generation of randomisation numbers, no central management of allocation were founded. (This study was published in German and Frank Peinemann provided the information).
Wang 1997	The study was not randomised due to the patients being divided according to the degree of greasiness of their facial skin.
Wilkinson 1966	The study design was not eligible for inclusion (not RCT).
Wilson 2007	The type of intervention was ineligible for inclusion.
Woodruff 2013	The study was published as an abstract. No randomisation was reported or implied and the study author could not be contacted.

RCT: randomised controlled trial
TCA: trichloroacetic acid