Licorice Extracts—Licorice extracts have been safely used in several cosmeceutical skin lightening products.10 The main active compounds in licorice root are glabridin and liquiritin, which work to disperse melanin. These compounds often are used topically at concentrations of 10% to 40%. A study by Amer and Metwalli11 found that topical liquiritin produced a reduction of pigmentary intensity, with 80% of patients showing an excellent response, which was described as no difference between the previously pigmented area and the normal skin surrounding it.
Aloesin—Aloesin is a low-molecular-weight glycoprotein found in aloe vera plants. Its mechanism of action includes competitive inhibition of the dihydroxyphenylalanine oxidation site, resulting in the inhibition of tyrosinase.12 It often is combined with arbutin for an enhanced lightening effect.
Niacinamide—Niacinamide is a form of vitamin B3 that works by suppressing the transfer of melanosomes to keratinocytes.13 In addition to its skin lightening effects, it also is photoprotective and antimicrobial, and its tolerability and safety have led to its inclusion in many cosmeceutical and prescription products.14
Ascorbic Acid—Ascorbic acid affects the monopherase activity of tyrosinase, thus reducing the synthesis of melanin. It also serves as an antioxidant in the skin by preventing the production of free radicals that can induce melanogenesis.15 Although it tends to be well tolerated with a low adverse effect profile, its relative instability and varying permeability can present a challenge. It is less effective as a monotherapy, so it often is combined with other lightening ingredients for greater efficacy.
Corticosteroids—Topical corticosteroids are anti-inflammatory and impact melanogenesis, though the mechanism of action of the latter has not been fully elucidated.16,17 Low- to mid-potency topical steroids often are used in conjunction with skin lightening products to diminish irritation and decrease inflammation.18 However, prolonged use of corticosteroids can lead to cutaneous adverse effects such as striae, hypopigmentation, and acne, as well as systemic side effects if there is sufficient absorption over time.
Soybean Extracts—Soybean extracts contain serine protease inhibitors that reduce the transfer of melanosomes into keratinocytes by inhibiting the PAR-2 (protease-activated receptor 2) pathway.19,20
Ellagic Acid—Ellagic acid is found in common plants such as eucalyptus and strawberry as well as green tea.21 It works as an antioxidant and decreases melanogenesis through inhibition of tyrosinase activity.