Cysteamine is an amino thiol that is endogenously derived from coenzyme A degradation.63 The exact mechanism of cysteamine’s action as a skin lightening agent is incompletely understood. At low concentrations, cysteamine facilitates the intracellular synthesis of glutathione (the antimelanogenic properties of which were described in the preceding section), and is itself a direct scavenger of hydroxy radicals.63 Early studies conducted on black goldfish revealed cysteamine to be a more potent depigmenting agent than HQ.64,65
Two recent studies in Tehran have found cysteamine 5% cream to produce statistically significant decreases in MASI scores and melanin indices when employed as a treatment for epiderma melasma.66,67 In each randomized, double-blind, placebo controlled study, patients received either placebo or cysteamine 5% once daily for 4 months. Both studies were designed similarly, with only minor differences in the number of patients enrolled and devices used to measure melanin indices. Mansouri et al66 (n=50) measured melanin indices solely with the Mexameter® skin colorimeter, whereas Farshi et al67 (n=40) measured melanin indices with both the Mexameter® and Dermacatch® skin colorimeters. One recent case report described a 44-year old woman who was transitioned to cysteamine cream after experiencing steroid atrophy secondary to the chronic daily use of Kligman’s formula (5% HQ, 1% dexamethasone, 0.05% retinoic acid) for recalcitrant melasma.68 Cysteamine cream was applied for 15 minutes nightly, and after 4 months obtained striking improvements in hyper- and hypopigmentation, erythema, and telangiectasias, as well as significant improvements in MASI score and melanin index. Her result was sustained with twice weekly application of cysteamine cream for maintenance, which she continued for 3 years without adverse effects or lesion recurrence.