Cysteamine 5% works on melasma. Not as fast as your retinoid worked on acne, with a real smell problem, and not for everyone. A 2024 meta analysis of seven randomized trials found a real effect over placebo. Visible fading lags by weeks, some people don't respond to any topical, and the smell is the practical hurdle.
Day 1. Unscrew a tube of cysteamine 5% over the bathroom sink and the first thing you notice is the smell: sulfur, like a struck match.
One ingredient. Twelve weeks. This piece walks through what the published trials say cysteamine 5% does to melasma, week by week, and what real life use asks of you.
Why cysteamine?
Melasma is the dermatology problem that humbles everyone. Hydroquinone, the gold standard for forty years, lost over the counter status in the United States in 2020 and now carries an ochronosis risk that scales with duration of use. Tretinoin helps, slowly. Oral tranexamic acid helps when the dermatologist will prescribe it. Lasers can drive pigment in the wrong direction in skin of color. Into that gap walked cysteamine, an aminothiol your own kidneys synthesize in trace amounts. A 2024 meta analysis in Archives of Dermatological Research pooled seven randomized controlled trials and clocked cysteamine 5% at a standardized mean difference of negative 0.84 versus placebo on the Melasma Area and Severity Index, with a 95% confidence interval of negative 1.19 to negative 0.49. That is a real effect size. Not marketing.
Week 1: the smell is the story
Cysteamine smells. Specifically it smells like a struck match, or like a hardboiled egg you forgot at the bottom of your bag. The odor is sulfur, released when the molecule oxidizes against your skin's surface. DermNet NZ describes the smell as the molecule's working signal: when you can smell it, it's reacting. The catch is that it reacts on you, in your apartment, around the people you live with.
The application protocol is the other half of why the smell is survivable. Cysteamine isn't a leave on. You apply for roughly 15 minutes, then wash. That short contact window is part of how the formula manages the odor, and it means you have to time the wash off.
How does cysteamine actually work?
The mechanism is the most interesting part of cysteamine, because the molecule does two things at once. It inhibits tyrosinase, the rate limiting enzyme in melanin production, by chelating the copper ion at the enzyme's active site. That is the same active site hydroquinone targets, but cysteamine reaches it without generating the cytotoxic semiquinone radicals that hydroquinone produces. The 2024 clinical efficacy meta analysis describes this dual action in detail.
The second mechanism is the one most marketing copy skips. Cysteamine doesn't only block tyrosinase. It also intercepts dopaquinone, an upstream intermediate, and shunts it into the synthesis of pheomelanin instead of eumelanin. Pheomelanin is the yellow red form of pigment your skin still produces in the presence of cysteamine, but in lower quantities and with a fundamentally lighter visual signature than the dark brown eumelanin you started with. Your face keeps making pigment. It just makes a different kind.
That distinction matters for two reasons. First, the depigmentation you see on cysteamine is a recoloring, not a bleaching, which is part of why ochronosis has not been reported with the molecule. Second, the effect fades when you stop, because tyrosinase activity returns and the pheomelanin pheomelanin dopaquinone shunt closes. Cysteamine is maintenance, not cure. The published trials that show the largest effect sizes all dose nightly for 12 to 16 weeks of induction and then taper to twice weekly indefinitely.
Week 4: nothing visible yet
At four weeks, expect to see little or nothing in the mirror. That tracks with the literature. The original Mansouri RCT from 2015, published in the British Journal of Dermatology, enrolled 50 patients with epidermal melasma across four months and reported that visible MASI separation between cysteamine and placebo emerged most strongly at the eight week timepoint, not at four. The trial used a colorimetry device called Dermacatch to measure pigment density objectively, because cameras lie and bathroom mirrors lie worse.
This is the part of every melasma treatment story that no influencer wants to write. It's the boring middle. It's also when most people quit.
Week 8: the inflection
Week 8 is where the Mansouri trial saw its clearest separation between cysteamine and placebo.
The mechanism behind the lag is the slow tyrosinase wind down. Cysteamine doesn't bleach existing pigment. It starves new pigment production while the old keratinocytes already loaded with melanin shed on their normal 28 day cycle. That is why the visible curve lags the molecular curve by roughly six weeks, and it's why anyone who quits at week four quits one cycle before the math begins to show on their face.
Week 12: what the trials show
By week 12, pooled data is a better guide than any single face, and the 2024 meta analysis above found a real improvement in MASI over placebo. Not everyone gets there. A pooled result is an average, and it cannot tell you in advance whether your melasma will be one that responds.
For timing, a 2023 review in the Journal of the American Academy of Dermatology by Dr. Andrew Alexis and Dr. Susan Taylor on best practices for melasma in skin of color frames a clinically meaningful response over a 12 to 16 week window.
How long the melasma has been there matters too. The literature on this is consistent. Older melasma responds less. Newer melasma responds more.
Cysteamine is not a time machine.
Who responds, and who doesn't?
Beyond the age of the melasma, the biggest variable is light, and it matters more than any cream. Melasma is a UV and visible light driven condition. A tube of cysteamine cannot outrun an unprotected lunch break. Dermatologists commonly pair melasma treatment with a tinted mineral sunscreen containing iron oxides, because visible light in the 400 to 500 nanometer range will keep melanocytes hyperactive regardless of what tyrosinase inhibitor sits on top.
Where cysteamine fits
Dr. Andrew Alexis, professor of clinical dermatology at Weill Cornell Medicine and one of the most cited voices on melasma in skin of color, has positioned cysteamine in trade journals as part of a category of non hydroquinone tyrosinase inhibitors worth folding into combination therapy rather than treating as a standalone fix. A combination plan might pair it with daily SPF 50, a tinted mineral sunscreen for visible light, and a low strength tretinoid at night on the evenings between cysteamine applications.
Cysteamine is one lever in a stack. The lever works. The stack matters more.
One combination is worth asking a dermatologist about. Tranexamic acid attacks melasma from the vascular side, which is a different pathway than tyrosinase inhibition. There is also a small early literature on cysteamine plus picosecond laser for recalcitrant cases.
What to know before you start
Plan for more than 12 weeks. The published trials that show the largest MASI deltas dose nightly for 12 to 16 weeks before tapering. Pair it with a daily SPF and a tinted mineral overlay, because sun protection is the one variable melasma cannot tolerate. And judge progress carefully: skin tone bias in standard photography is real, and a bathroom mirror is a poor instrument for a slow change in pigment.
Take the smell seriously too. A daily sulfur smell can change a morning routine. Smell is part of the compliance equation.
Timing helps. The published trials almost all dose the molecule at night, which is logistically easier and means the residual odor fades during sleep rather than during a meeting.
The price is worth checking before you commit to a 16 week course. Telederm is not an obvious shortcut for this molecule. Musely's melasma cream, The Spot Cream, costs $36 a month but draws on other actives, such as hydroquinone, tranexamic acid and tretinoin, and its treatment list shows no cysteamine product.
If you are reading this because your own melasma has not budged on whichever niacinamide serum the algorithm sold you last, or on the same vitamin C serum that oxidized in your bathroom six weeks ago, cysteamine is a real next step worth a conversation with a dermatologist who has used it. The data is replicated. The mechanism is clean. The smell is, in the end, survivable. Photograph the tube and Skinventry shows its published ingredient list, who makes it, and who owns the brand, each with its source.
The verdict: worth it for the right melasma, on the right face, with the right sunscreen. Just not at the price your nose pays in patience.
