Cysteamine, an aminothiol, is naturally present in human body cells as an antioxidant originating from the degradation of Coenzyme A. Physiologically, it is distributed well in mammalian tissues. 

Cysteamine is highly concentrated in human milk, which acts as an intrinsic antioxidant and has a protective role. Multiple studies have reported that cysteamine is a highly effective skin depigmenting agent. Earlier, its rapid oxidation and very offensive odor challenged its topical use until recently, stabilization of cysteamine was accomplished. This has caused an acceptable galenical form for topical application. Since 2015, multiple clinical studies, as well as case reports, have shown the efficacy, safety, and tolerability of stabilized cysteamine (st.Cys).  

Two double-blind, randomized, and vehicle control trials have also demonstrated Stabilized cysteamines substantial effectiveness in treating melasma.

Stabilized cysteamine (st.Cys) has shown equal efficacy to well-known depigmenting therapies, like triple combination cream or tranexamic acid mesotherapy, with higher tolerability. A recent clinical trial has shown the marked efficacy of topical cysteamine for treating senile lentigines, which are usually considered resistant to topical depigmenting agents. Hence, Topical stabilized cysteamine can be one of the most potent treatments for hyperpigmentation disorders in humans.

Desai S, Hartman C, Grimes P, Shah S. Topical Stabilized Cysteamine as a New Treatment for Hyperpigmentation Disorders: Melasma, Post-Inflammatory Hyperpigmentation, and Lentigines. Journal of Drugs in Dermatology : JDD. 2021 Dec;20(12):1276-1279. DOI: 10.36849/jdd.6367. PMID: 34898155.