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Hydroquinone: Is the Cure Worse Than the Problem?
By: Diana Howard, PhD
Posted: March 27, 2009, from the April 2009 issue of Skin Inc. magazine.
page 2 of 5
For whatever reason, hydroquinone still remains the only ingredient recognized as a “lightening agent” by the U.S. Food and Drug Administration (FDA), and its use falls under the regulations as stated in the monograph on skin lightening, which designates hydroquinone as the sole acceptable lightening agent. This means that the use of other ingredients for treating hyperpigmentation cannot be called skin-lighteners or whiteners, so the industry has coined the term “brightener” for these nonhydroquinone alternatives. As recently as 2007, the FDA reported its intent toward banning the use of hydroquinone in nonprescription products due to safety issues, but as of yet has not implemented any new regulations. The Cosmetic Ingredient Review (CIR) Board has agreed to revisit the safety of hydroquinone and report back by March 2009. Perhaps the FDA is awaiting the new report before passing any new regulations or amending the monograph on lightening.
Alternatives to hydroquinone
Most of the safe alternatives to hydroquinone impact the key enzyme, tyrosinase, that mediates two key steps in melanogenesis. See Key Steps in Melanin Biosynthesis.
Key ingredients. There are several ingredients that inhibit the tyrosinase enzyme, as well as compete with the enzyme’s substrate, L-3,4-dihydroxyphenylalanine (L-DOPA). Botanical extracts, such as Ferula foetida (giant fennel), bearberry, licorice, Sophora angustifolia, kiwi fruit, nasturtium, rumex (yellow dock), Phyllanthus emblica fruit and mulberry contain bioflavonoid components similar in chemical structure to L-DOPA, the end product of Step 1, illustrated in Key Steps in Melanin Biosynthesis. The bioflavonoids compete with the substrate L-DOPA, thereby preventing Step 2, also illustrated in the diagram, from occurring.
Tyrosinase inhibitors. Tyrosinase inhibitors also exist, such as hydroxycinnamic acid, gluconic acid, zinc glycinate, kojic acid, aspergillus ferment, rumex extract and ergothioneine, that chelate or bind copper, a cofactor required in Step 2 of the diagram. Binding the copper inhibits this reaction from occurring and controls melanin formation.
Hydroxy acids. Although the use of hydroxy acids—lactic acid, glycolic acid and salicylic acid—in skin-brightening products has generally been utilized to accelerate desquamation and removal of melanin-containing corneocytes, it has recently been shown that a 5% concentration of lactic acid will inhibit the formation of the tyrosinase enzyme, thereby slowing the process of melanin synthesis. Other exfoliating agents used in brightening products include pumpkin enzyme, sutilains (a protease enzyme), lactobacillus ferment and galactoarabian, a molecule that stimulates natural desquamation in the skin.