OPINION | SKIN PIGMENTATION | hyperactive and abnormal
melanocytes, where it has an antiproliferative effect, as well as inhibiting tyrosinase. It is used medically in the treatment of acne and certain other skin conditions, including melasma and rosacea. It has also been studied in the treatment of psoriasis. Azelaic acid has been the subject of a
number of formal clinical trials. In one study1
, 20%
azelaic acid cream appeared to be more effective than 4% hydroquinone in reducing mild melasma. A study to compare the safety and effectiveness of azelaic acid gel to hydroquinone cream in the treatment of melasma is currently underway at The Callender Center for Clinical Research Recruiting in Mitchellville,
Maryland,
More powerful lasers
abnormal melanocytes, although the use of this technique to treat
while a controlled, single- blinded investigation of the efficacy, tolerability and safety of azelaic acid iontophoresis compared with topical treatment with azelaic acid cream in female patients with melasma is being carried out at the Department of Dermatology at the Medical University of Vienna. Improbably, a component of many
skin-lightening products is liquorice extract. A whole range of pharmacological properties have been ascribed to liquorice over the years, but a combination of liquorice extract, betamethasone and retinoic acid has been reported to be highly effective in
may also be used to ablate superficial segments of the skin including
hyperpigmentation is not regarded as a first-line therapy.
lightening the skin. The active ingredient of liquorice in this situation appears to be glabridin, which has been found to inhibit tyrosinase activity as well as superoxide anion production and cyclooxygenase activity. There do not appear to have been any clinical studies of glabridin itself in the context of skin lightening, although another component of liquorice, liquirtin, which does not inhibit tyrosinase but acts via other mechanisms, has been shown to be effective in treating melasma. Meanwhile kojic acid, a
metabolite found in a range of fungal species (and a by-product in the manufacture of sake, Japanese rice wine), has been found to chelate copper ions at the active site of tyrosinase, thus
inhibiting the enzyme and inhibiting the formation of melanin. It also acts as an antioxidant, simultaneously acting further along the metabolic pathway from tyrosine to melanin. Its potential as a skin lightening agent has been recognised for some time, and a cream formulation of kojic acid with hydroquinone, for the depigmentation of skin, was launched by the Spanish company Vi— as over a decade ago. More recently, derivatives of kojic acid
have been synthesised that display greater skin penetration than kojic acid itself, and greater melanin-inhibitory activity.
Medical devices Finally, certain types of hyperpigmentation can be successfully treated using medical devices rather than chemical agents. Treatment of pigmented lesions such as lentigines (conditions where areas of skin have an increased number of melanocytes), using a Q-switched (i.e. pulsed) ruby laser emitting at 694 nm or a Q-switched Nd:YAG laser emitting at 1064 nm, is generally effective. The principle of the treatment is that laser energy is absorbed by melanin-containing cells in the skin, which are thus destroyed. Laser treatment is sometimes associated with adverse effects such as mild discomfort or redness of the treated area. A recent advance in laser treatment has been fractional photothermolysis. The technique, which has a number of cosmetic applications such as removal of crowÕs feet or minor scarring, as well as minimising the appearance of age spots, uses laser energy to stimulate collagen production in the upper layers of the skin, which smoothes the skin and helps to disguise heavily pigmented areas. More powerful lasers may also be used
to ablate superficial segments of the skin including abnormal melanocytes, although the use of this technique to treat hyperpigmentation is not regarded as a first-line therapy.
In addition, some
hyperpigmentation disorders respond to treatment with intense pulsed light at 515–1200 nm.
Conclusions A recent report predicted that the global market for skin lightening products and services could be worth $10 billion by 2015, with the strongest growth being seen in Asia and Japan. There are therefore significant opportunities to be had, particularly if the trend away from the use of hydroquinone increases the demand for alternative treatments.
References
1. Balina LM, Graupe K. The treatment of melasma. 20% azelaic acid versus 4% hydroquinone cream. Int J Dermatol 30(12):893-5 (1991 Dec).
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