Until recently, hydroquinone or hydrochinone was the most powerful active ingredient for treating hyperpigmentation. But serious concerns about its safety – particularly its risk of causing cancer – led the EU to ban its use in 2001. It’s still available in some over-the-counter remedies in the US, but only in low concentrations of 2% or less. Hydroquinone can also cause post-inflammatory hyperpigmentation, as it’s a skin irritant.
Arbutin is a natural source of hydroquinone, and is one of the key ingredients used in skin whitening products in Asia. It’s not as strong or effective as industrially produced hydroquinone, but there are concerns that it carries similar cancer risks.
Kojic acid is a by-product of the fermentation process involved in producing the Japanese rice wine, sake. It’s considered to be a relatively safe and natural option, but it’s a fairly weak inhibitor of melanin production.
Vitamin C derivatives have been shown to be relatively effective against hyperpigmentation. They’re often used in conjunction with other active ingredients.