Long established as the most effective ingredient for treating brown spots. Hydroquinone does not bleach the skin, which is why “bleaching agent” is a misnomer; it can’t remove pigment, it works by inhibiting the synthesis of excess melanin before it can appear on skin’s surface.
Over-the-counter hydroquinone products can contain 0.5% to 2% concentrations of hydroquinone; 4% (and sometimes higher) concentrations are available only from physicians.
Some concerns about hydroquinone’s safety on skin have been expressed, but despite the controversy, abundant research from reputable sources shows hydroquinone to be safe and effective. If you’re struggling with brown spots or skin discolorations, hydroquinone remains among the best ingredient to treat them.
A reminder that no skin-lightening ingredient will work to lighten brown spots if you’re not diligent about daily application of a broad spectrum sunscreen. Unprotected sun exposure is the root cause of most dark spots, so forgoing sunscreen means you won’t see the results you want, no matter how well formulated the lightening product may be.
References for this information:
The Journal of Clinical and Aesthetic Dermatology, August 2014, pages 13-17
Journal of Drugs in Dermatology, March 2013, pages S32-S37
The Journal of Dermatological Treatment, September 2010, pages 272-275
Journal of the American Academy of Dermatology, November 2007, pages 854-872
Dermatologic Therapy, September-October 2007, pages 308-313
Critical Reviews in Toxicology, October 2007, pages 887-914; and May 1999, pages 283-330
Journal of the European Academy of Dermatology and Venereology, August 2006, pages 781-787
Journal of Toxicology and Environmental Health, June 1998, pages 301-317