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Talking Tone: Melanin Under the Microscope
By: Laura J. Goodman
Posted: March 27, 2009, from the April 2009 issue of Skin Inc. magazine.
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The desire for even-toned skin is certainly driving clients to seek professional advice. For years, it has been chemical peels, microdermabrasion and laser resurfacing that have been used to treat age spots and other skin imperfections associated with aging and long-term sun exposure.10–13 Removing the outermost layers of skin through exfoliation has been proven as a means to help improve skin texture and tone, and these treatments are still on the rise. According to the American Society of Plastic Surgeons, chemical peels and microdermabrasion were both in the top five minimally invasive cosmetic procedures in 2007, and laser resurfacing treatments also increased by 32% from 2006 to 2007.14
In addition to resurfacing treatments in the clinic or spa, there are also a host of take-home products for topical application with ingredients such as alpha hydroxy acids and linoleic acids that have been shown to encourage exfoliation. Several other ingredients also have been shown in laboratory studies to interrupt the melanogenesis cycle and reduce the outward signs of hyperpigmentation and uneven skin tone.
Hydroquinone is currently considered the gold standard for depigmentation. Right now, it is available in consumer-use products with levels up to 2%, and up to 4% by physician’s prescription. And though hydroquinone is highly effective at interrupting the melanogenesis cycle, it does have several known adverse effects, including irritation, post-inflammatory hyperpigmentation or increased darkening of the skin, nail discoloration and occasionally hypopigmentation—the complete loss of pigmentation or bleaching of the skin.
In years past, the focus has been on ingredients that inhibit the tyrosinase enzyme, the key enzyme involved in the production of melanin. Ingredients such as kojic acid; arbutin; ascorbic acid, or vitamin C; ellagic acid; licorice; sulfhydryl compounds; and resorcinols are effective tyrosinase enzyme inhibitors, and laboratory studies have also shown some of these ingredients have other effects. For example, ascorbic acid and sulfhydryl compounds are also effective antioxidants, which help to protect from free radical damage when applied to the skin’s surface. “It is difficult to directly connect a specific mechanism of an ingredient to the observed effect on pigmentation,” notes P&G Beauty scientist Donald L. Bissett, PhD.
More recent targets explored in the melanogenesis cycle include both the inhibition of glycosylation, a sugar chain reaction necessary for the production of melanin, and preventing the transfer of packaged melanin from the melanocyte cell to the keratinocyte cell. N-acetyl glucosamine (NAG) is an ingredient that has been shown to inhibit the sugar chain reaction, and ingredients such as soybean trypsin and niacinamide are reported to reduce the amount of melanin transferred from cell to cell.