Cysteamine is approved by the FDA to treat cystinosis, which is a lysosomal storage disease. However, cysteamine also has been shown to have skin-lightening effects and to inhibit melanogenesis. It is available in Europe, and may also be found in some cosmeceutical products. It has been investigated in the treatment of melasma in two randomized clinical trials (study 1, study 2). In both studies, melasma was reduced after several months of use. Erythema, dryness, itching, burning, and irritation were noted as side-effects.
Cysteamine is not readily available in the United States, but can be compounded by specialty pharmacies.
Cysteamine may be an up and coming treatment for melasma, possibly eventually challenging the gold-standard hydroquinone.