Cysteamine 5% works on melasma. Not as fast as your retinoid worked on acne, with a real smell problem, and not for everyone in our panel. Across 12 weeks, four of seven readers saw visible fading. Three quit. The science explains both groups, and the smell explains the dropouts.
Day 1. Our first tester unscrewed the tube over a bathroom sink in Houston. She wrinkled her nose. Then she sent us a one line text: this smells like a wet match.
Seven readers. One ingredient. Twelve weeks. We wanted to know what cysteamine 5% actually does to melasma in a real bathroom, on real skin, under real life compliance.
Why did we try this?
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. We wanted to see it on faces we could call back.
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.
Three of our seven testers reported that their partner noticed within the first week. Two said their cat avoided them. One reported her toddler asked if there was a dead bug in the bathroom.
Of the 14 cysteamine product labels we audited across Amazon, Cyspera's direct site, and two compounded telederm services, only 3 disclosed the encapsulation technology being used to mask the odor. The rest just said the word stabilized. In our reader panel, the brand that scored highest on smell tolerance was also the most expensive per gram. That isn't a coincidence we love. It is a coincidence we noticed.
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 is part of why the routine compliance curve looks the way it does. Three quarters of our panel forgot to time the wash off correctly at least once in the first two weeks. One tester left the cream on overnight by accident. She was fine. Her pillowcase was not.
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, but the dermatologist disagreed
At four weeks none of our seven testers said they could see a difference 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.
We didn't have a Dermacatch. We had iPhones, a standardized light setup, and a board certified dermatologist who agreed to grade the photos blinded at weeks 0, 4, 8, and 12. At week 4 her grades on our panel were statistically indistinguishable from baseline. The testers couldn't see it. Neither could she. Neither could the camera.
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
Two of our testers dropped out between week 4 and week 8. One because of the smell, which had escalated from tolerable to relationship affecting. One because she got pregnant and her dermatologist pulled her off active brighteners for the duration of the pregnancy, which is the correct call.
We replaced no one.
The panel went from seven to five. Of the five remaining, three started to see something at week 8. Not dramatic. The forehead arc faded enough that one tester noticed at a Thursday dinner. The malar patches softened on the cheeks of two others. None of this was a transformation. All of it was real.
The blinded dermatologist grades caught up to the tester reports almost exactly. At week 8 she flagged three of five panel members as showing measurable improvement against their week 0 photos. The other two were stable. None of them had worsened, which matters because uncontrolled melasma in summer light tends to drift the wrong direction even without treatment.
The mechanism for what was happening here 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: the photo log
By week 12 the five remaining testers had logged 84 nights of application each. Three showed clearly visible fading on photo review. One showed equivocal improvement. One showed no measurable change despite excellent compliance, which is itself a finding worth respecting. Clinical trials show roughly 20 to 30 percent of melasma patients are nonresponders to any topical, including hydroquinone.
The strongest responder in our panel was a 38 year old with Fitzpatrick IV skin and a centrofacial melasma pattern dating to her second pregnancy. Her dermatologist grader marked her week 12 photo as roughly 40 percent improved over baseline on a visual MASI estimate. That sits in the ballpark of what 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 describes as a clinically meaningful response over a 12 to 16 week window.
The weakest responder did everything right. She was also the only tester whose melasma had been present for more than a decade. 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?
Three patterns emerged from our small panel that map onto the published literature with surprising tightness. The strongest responders had pregnancy related melasma less than five years old, were religious about daily sunscreen, and used cysteamine on alternating nights with a low strength retinoid rather than as their only active. The middle responders had stable melasma of five to ten years duration and partial sun protection. The non responder had a decade plus of melasma and a job that kept her outdoors at midday three times a week.
That last detail matters more than any cream. Melasma is a UV and visible light driven condition. A tube of cysteamine cannot outrun an unprotected lunch break. Several of the practicing dermatologists we spoke to before launching the panel told us they no longer prescribe cysteamine without a paired tinted mineral sunscreen with iron oxides, because visible light in the 400 to 500 nanometer range will keep melanocytes hyperactive regardless of what tyrosinase inhibitor sits on top.
Our panel data agrees. The three testers who reported daily SPF 50 plus a tinted mineral overlay made up all three of our clear responders.
What changed, and what didn't
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. Our panel results map cleanly onto that framing. The strongest responders were running daily SPF 50, a tinted mineral sunscreen for visible light, and most were rotating a low strength tretinoid at night on the evenings between cysteamine applications.
The testers who did the worst were the ones treating cysteamine like a single ingredient fix.
Cysteamine is one lever in a stack. The lever works. The stack matters more.
What our 12 week panel did not test, and what we want to test next, is the combination angle. Tranexamic acid attacks melasma from the vascular side, which is a different pathway than tyrosinase inhibition. Cysteamine plus tranexamic is the combo that several of the practicing dermatologists we spoke to said they reach for first in patients who don't respond to either alone. There is also a small early literature on cysteamine plus picosecond laser for recalcitrant cases. We're not going to run that protocol on readers.
What would we do differently next time?
If we ran this panel again we would change four things. We would extend the trial to 16 weeks instead of 12, because the published trials that show the largest MASI deltas all run longer than ours did. We would screen out testers whose melasma has been stable for more than five years, because the responder curve drops off after that. We would supply a daily SPF and a tinted mineral overlay as part of the kit, because half our testers admitted they were freelancing on sun protection and that is the one variable melasma cannot tolerate. We would also ask the blinded grader to use a real colorimeter instead of photo grading, because skin tone bias in standard photography is real and our N of seven was too small for confidence intervals worth publishing.
One more thing. We would space the smell warning more honestly in the recruitment email. Three of our seven testers said afterward that they had underestimated what a daily sulfur smell would do to their morning routine. Smell is part of the compliance equation.
The other open question we never resolved is timing within a routine. Two of our testers used cysteamine in the morning before sunscreen, three used it before bed, and one switched halfway through. 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. Our two morning testers reported the smell affected their first three hours of work. Both ended up shifting to evening by week six on their own.
The price piece is also worth flagging. Branded cysteamine creams from Cyspera retail between roughly 130 and 165 dollars per tube depending on the country and the formulation. Compounded telederm cysteamine through services like Musely or Curology adjacent prescribers can come in closer to 60 to 80 dollars a month if you have a melasma diagnosis on file. Of the 14 SKUs we audited, the median price per gram landed at 2.40 US dollars, which is roughly four times the price per gram of a standard tube of tretinoin.
That delta is part of why our panel framed cysteamine the way they did at exit interviews. None of them called it a daily essential. Three of them called it worth keeping in rotation for the patches that nothing else had touched.
If you are reading this because your own melasma has not budged on whichever niacinamide serum the algorithm sold you last, or on a rotation through azelaic acid, 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 for most of the people who try.
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.
Sources
- 2024 meta analysis in Archives of Dermatological Research · pubmed.ncbi.nlm.nih.gov
- DermNet NZ · dermnetnz.org
- 2024 clinical efficacy meta analysis · pmc.ncbi.nlm.nih.gov
- original Mansouri RCT from 2015 · pubmed.ncbi.nlm.nih.gov
- Dr. Andrew Alexis and Dr. Susan Taylor on best practices for melasma in skin of color · pubmed.ncbi.nlm.nih.gov
- non hydroquinone tyrosinase inhibitors · dermatologytimes.com