Ingredient Beauty BenefitsInternational non-proprietary name · Hydroquinone
Hydroquinone: all of its evidence here came from other ingredients' trials
It is the name that appears most often as a comparator on this site, and not one trial here was designed to measure hydroquinone. All three were designed to measure something else, with hydroquinone as the control arm. What that arm did: 4% cream lowered the melasma score (mMASI) by an average of 33% over 90 days (95% CI 23–42%). And it did not differ significantly from thiamidol, cysteamine or tranexamic acid.
Last checked Oct 6, 2026
Start here
- What it is
A topical drug that lightens pigment by blocking the enzyme that makes melanin. It is called the old first-line choice for melasma.
- What it is used for
For melasma and pigmentation. It needs a prescription.
- How it is said to work
It is described as blocking tyrosinase and acting on the melanocyte directly.
There are no numbers and no citations in this box. What has been established, and how far, is below.
At a glance
- Category
- Prescription only
- How well established
- Moderate evidence
- Concentration studied
- 4%
- Length of the studies
- 8–16 weeks
“Concentration studied” and “Length of the studies” are taken straight from the research on this page. They are not a recommended dose, and the figure for each finding is written out in the text.
This is not how large the effect is but how well confirmed it is. It shows the highest grade among the findings on this page.
Whether and how to use it is decided with a doctor or pharmacist.
Hydroquinone is a topical drug that lightens pigment by blocking the enzyme that makes melanin. It is called the old first-line choice for melasma.
This page was written to fill a gap that the brightening comparison created. Hydroquinone is the name that appears most often in that table, and this site had no page for it. A comparison whose benchmark has no page is half a comparison.
And this page has something no other page here has: it was written without adding a single new source.
The three trials below were already registered on this site. They are the trials the thiamidol, cysteamine and tranexamic acid pages each carry as their 'tied with hydroquinone' entry.
That fact is the content of this page. All three ask whether another ingredient does as much as hydroquinone, not how much hydroquinone does. The control arm's number falls out of that question incidentally.
Which leaves the question of which way to read 'it tied'.
- read from the other ingredient's side — 'something available without a prescription did as much as a prescription drug'
- read from hydroquinone's side — 'the old first-line choice was no different from the new actives'
Both come out of the same material, and all of it is 20 to 50 people. This site does not read a failure to find a difference between two active treatments at that size as 'the same'. It can be because there is none, or because there was no power to find one.
Finally, that this is a prescription drug is what makes the comparison practical. If the side that needs a prescription tied with the side that does not, that information is about access more than about effect size.
This site does not give instructions for using medicines. Prescribing and taking are settled in a clinic.
What is established
All three were designed to measure something else, with hydroquinone as the control
Three randomised trials, each with 4% hydroquinone cream as the comparator. And in all three, something else is the subject.
One — a 2021 Brazilian trial (50 people, 90 days)
Fifty women with facial melasma were randomised to 0.2% thiamidol (twice daily) or 4% hydroquinone (at bedtime). Assessor-blinded, with both arms also using an SPF60 tinted sunscreen.
- hydroquinone arm: mMASI fell by an average of 33% (95% CI 23–42%)
- the thiamidol arm fell 43% (35–50%)
- no difference between arms (P ≥ .09)
Two — a 2021 cysteamine comparison (20 people, 16 weeks)
5% cysteamine against 4% hydroquinone, with no significant difference between the arms. The detail is on the cysteamine page.
Three — a 2024 tranexamic acid comparison (20 people, 8 weeks)
3% tranexamic acid cream against 4% hydroquinone, split-face. On the tranexamic acid page this trial is recorded as early evidence.
How to read it.
First, none of the three was built to measure hydroquinone. The design question was whether a new active does as much. The 33% in the hydroquinone arm falls out of answering that question. This site uses the figure and writes down that this is where it came from.
Second, and yet we gave it moderate. It meets all the conditions — three separate randomised trials, a graded endpoint, not all industry-funded. Mechanically that reaches 'strong'. We did not raise it. Two reasons.
- all three are 20 to 50 people. That is small for separating two active treatments
- a control arm's performance is not the value the trial spent its power on. The primary endpoint sat on the other ingredient
It is the same judgement as lowering the badge by hand on the lactoferrin page.
Third, there is no placebo-controlled trial on this page. We have not yet read a trial of hydroquinone against vehicle in the original. For a drug used this long such material surely exists — we simply have not opened it. We will write it when we have.
Fourth, sunscreen was in both arms. In the Brazilian trial both sides used SPF60. What the result is without it, this trial does not show. It is the sentence this site keeps writing about melasma.
Fifth, the durations are 8 to 16 weeks. Melasma recurs, and this length says nothing about what happens after stopping.
So it sits at 'moderate'. And to say exactly where that badge hangs — 4% hydroquinone tied with each of three new actives.
- Randomised controlled trial in people · 50 participants · 13 weeks · Compared with another active ingredient · Funding not declared · Endpoint scores from blinded assessors PMID 33988887 · abstract read
- Randomised controlled trial in people · 20 participants · 16 weeks · Compared with another active ingredient · Funding not declared · Endpoint scores from blinded assessors PMID 32981068 · abstract read
- Randomised controlled trial in people · 20 participants · 8 weeks · Compared with another active ingredient · Funding not declared · Endpoint scores from blinded assessors PMID 38918942 · abstract read
Known risks
This site does not give instructions for using this drug. It is prescription-only; what follows is what to know while reading.
Irritation and contact dermatitis have been reported. In the Brazilian trial above, allergic contact dermatitis was confirmed in 2 of the thiamidol arm (8%). We could not find the breakdown of adverse events in the hydroquinone arm in that abstract.
Pigment darkening with long use has been reported for this drug. We have not yet opened material that would let us write its frequency or the conditions. We will neither frighten without numbers nor write as if it does not happen — this one line is all we have verified. How long to use it is for whoever prescribes it.
Sun avoidance has to go with it. All the trials above used sunscreen alongside. See sunscreen.
Material on use in pregnancy is not on this page. If you are pregnant or planning to be, that is a matter for a clinic.
Nor is there material here on using it with other brightening actives. The kojic acid page has an entry about 'adding it to a gel that already worked', and that gel was a combination containing hydroquinone. Material about a combination is material about a combination.
What is not established
- No placebo-controlled trial is on this page. We have not yet read a trial against vehicle in the original. It is this page's largest gap.
- We have not opened the primary Korean authorisation record. Other pages on this site say it is prescription-only in Korea, and we have not yet attached the primary source for that sentence here. That is why the regulatory class says 'being verified'.
- We could not put numbers on the risk of long use. Exactly as written under risks above.
- There is no comparison between concentrations. All the trials above are 4%. We found no material on other strengths.
- Nothing looked past stopping. These are 8 to 16 week trials, and melasma recurs.
- Results by skin colour we could not verify. In melasma and pigmentation that is not a small gap.
- All the evidence on this page came from other ingredients' trials. We record that as a gap too — a control arm's performance is not the value the trial spent its power on.
Whether and how to use it is decided with a doctor or pharmacist.
What this article relies on
Unless marked otherwise, a paper was read to the abstract. Only papers whose full text we opened are marked as such.
- PubMed — 미국 국립의학도서관 문헌 데이터베이스National Library of Medicine · Checked on 2026-09-16