| dermatology | aRTicle
indicating that topical applications of zinc solution twice daily for 2 months was effective with a percentage of improvement of more than 50% according to the maSI score, with no significant side-effects other than a slight stinging sensation in some patients that subsides with continuous therapy21
. the exact mechanism cannot be
understood, but it might be attributed to its peeling, antioxidant, and sun-screen effects.
Arbutin arbutin, or arbutoside, is a glycosylated hydroquinone found at high concentration in certain plants, such as the ‘corbezzolo’ (strawberry tree) or ‘uva ursina’ (bearberry). It is a water-soluble compound, the optimal pH of which may be 5 or 7. Its mechanism of action seems to be related to the inhibition of tyrosine hydroxylase and doPa oxidase. this is a competitive mechanism caused by areas of tyrosine binding, so that arbutin inhibits the enzyme activity and not its production. arbutin is a precursor of hydroquinone, but there are studies which show that it is a more effective and less toxic skin lightener than hydroquinone as it can also be added to a number of topical compounds22
. the action of arbutin is dose–dependent and
less toxic than hydroquinone. deoxyarbutin is a recently developed derivative of arbutin that has been produced by removing the hydroxyl groups from the molecule. this produces reversible skin-lightening by direct inhibition of tyrosinase. although good controlled clinical trials are lacking, initial in vitro and in vivo experimental studies have demonstrated that it could be a safe and effective treatment for hypermelanotic disorders15
.
Azelaic acid azelaic acid is a natural, saturated straight-chain dicarboxylic acid, which has selective effects on hyperactive and abnormal melanocytes, such as the inhibition of tyrosinase, of the cell membrane-associated enzyme thioredoxin reductase, of specific mitochondrial dehydrogenases, and of dNa synthesis23
. the reported
preparations are 10%, 15%, 20% and 35%, the 15–20% preparation the most commonly used, which has also shown efficacy as a monotherapy. azelaic acid has to be applied twice daily for a number of (up to 8) months, even though lightening starts after 1–2 months. generally speaking, early cases respond better than those that are long-standing, and epidermal melasma generally responds faster than mixed melasma24, 25
. Side-effects are mostly mild with transient itching and
burning; however, acneiform eruptions and telangiectasia have also been reported, as well as rare cases of asthma, vitiligo and hypertrichosis26
. a combination of azelaic acid 20% cream and glycolic
acid 15% or 20% lotion in a clinical comparison with hydroquinone 4% was demonstrated by Kakita et al as effective in the treatment of moderate or severe melasma and other facial hyperpigmentation in darker- skinned patients, with only a slightly higher rate of mild local irritation27
.
Ellagic acid ellagic acid is an antioxidant substance that can be found in certain plants and in some nutrients such as green tea and strawberry20, 22
. recently, ellagic acid was
shown to inhibit skin hyperpigmentation and experiments in vitro have indicated that it suppresses melanogenesis by inhibiting tyrosinase activity22
. this
inhibition is caused by chelation of the copper atoms on the tyrosinase molecules. ellagic acid reacts to activated melanocytes, suppresses the melanogenesis, does not create any damage in cells, and has antioxidant properties. No significant side-effects have been described in the literature.
Kojic acid Kojic acid is one of the last depigmenting agents used to treat melasma. Chemically (5-hydroxy-2- (hydroxymethyl)-4-pyrone), it is an antibiotic produced by species of Aspergillus and Penicillum, with an anti-inflammatory and pain relief activity. Its whitening activity is a result of its slow-binding inhibition of tyrosinase28
preparations, twice daily for 2 months; higher concentrations do not improve its depigmenting activity. garcia et al have shown its efficacy in combination with 5% glycolic acid29
. those who do not respond to
hydroquinone and glycolic acid, may find the addition of kojic acid beneficial. the most significant side-effect of kojic acid is contact
allergy. this has been observed with a higher frequency in Japan, where the compound is widely used as a topical agent30
.
Mequinol mequinol is another phenolic derivative, which causes less irritation than hydroquinone in animal studies31 mechanism of action is unclear; however, being a
prime-journal.com | July 2011 ❚ Recently, ellagic acid was shown
to inhibit skin hyperpigmentation and experiments in vitro have indicated that it suppresses melanogenesis by inhibiting tyrosinase activity
Steroids a range of topical corticosteroids have been used in the treatment of melasma and other hyperpigmentary disorders. mild steroids (hydrocortisone 1%) have been used with poor results (20), while potent (betamethasone 2%) and very potent steroids (clobetasol propionate 0.05%) gave better results, as they have a better efficacy when combined with tretinoin or hydroquinone2, 15
are those typical of their long-term use; atrophy, itching, acne, and telengiectasias, especially frequent in areas more susceptible to local steroid damage (e.g. the face).
. the adverse effects of topical steroids
. Kojic acid is normally used in 1%
. Its 21
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