Table 1. Trials Comparing Hydroquinone to Other Skin-Lightening Agents.

HQ: Hydroquinone, KA: kojic acid, MASI: melasma area severity index, TA: tranexamic acid

Study	Treatment Groups	Results	Conclusions
Monteiro et al. [26]	4% HQ 0.75% KA and 2.5% Vitamin C	Decrease in MASI score in weeks 0-12, significant change from weeks 0-4 with 4% HQ treatment Decrease in MASI score in weeks 0-12, no significant change from weeks 0-4 with 0.75% KA treatment	The results of treatment with hydroquinone have an earlier onset than treatment with KA
Owolabi et al. [28]	Group A, control Group B, 2% HQ Group C, 2% KA Group D, 4% HQ Group E, 4% KA Group F, 2% HQ and 2% KA Group G, 4% HQ and 4% KA Group H, 4% HQ, 4% KA, and aloe vera	Groups B and D showed greater disruption of the stratum corneum Groups F, G, and H showed less disruption of the stratum corneum Groups A, C, and E did not cause observable disruption to the stratum corneum	Hydroquinone may cause greater disruption of the stratum corneum, while KA and aloe vera may ameliorate these effects
Marpaung et al. [29]	3% TA, 4% HQ	More significant decrease in MASI score and MI in 3% TA group	3% TA cream and 4% hydroquinone cream are effective in decreasing MASI score and MI
Arrowitz et al. [30]	0.2% Thiamidol-side vs. untreated side of face 0.2% Thiamidol-side vs. 2.0% HQ-side	Significant decrease in MASI score in thiamidol-treated side vs. untreated Decrease in MASI scores in both treated sides, more significant improvement in thiamidol-treated side, some worsening noted in HQ-treated sides	0.2% Thiamidol is more effective in the treatment of epidermal melasma than 2.0% hydroquinone