Cysteamine

Amino acid that breaks down melanin and brightens skin tone.

Also known as: L-cysteamine, cysteamine HCl, 2-aminoethanethiol

What it is

Cysteamine is a small amino acid derivative containing a reactive thiol (sulfhydryl) group. It's a reduced form of cystine and occurs naturally in the body in trace amounts.

What it does

Cysteamine works by reducing melanin through its thiol group, which breaks disulfide bonds in melanin polymers and converts them to colorless compounds. This leads to visible lightening of hyperpigmentation, melasma, and post-inflammatory hyperpigmentation. It also has mild antioxidant and anti-inflammatory properties.

The evidence

Strong clinical evidence supports cysteamine's efficacy for melasma and hyperpigmentation; multiple randomized controlled trials show 50–70% improvement in pigmentation over 8–12 weeks. Mechanism is well-established in vitro and in vivo.

Best for

Melasma, post-inflammatory hyperpigmentation, uneven skin tone, and general brightening in all skin types, especially darker skin tones.

Pairs well with

Hydroquinone, tretinoin, vitamin C, niacinamide, sunscreen (essential). Works synergistically with other depigmenting agents.

Use cautiously with

Avoid combining with strong oxidizing agents (benzoyl peroxide, high-dose vitamin C at extreme pH) as they may inactivate the thiol group. Use cautiously with other thiol-containing compounds.

Cautions

Can cause mild irritation, redness, or odor (sulfur-like smell) at higher concentrations. Pregnancy safety data is limited; consult physician. May increase photosensitivity; strict SPF 30+ sunscreen required. Patch test recommended.