Science › Clinical studies › Glutathione
Can a 2% glutathione lotion brighten skin?
A randomised, double-blind, split-face trial of 2% oxidised glutathione against placebo in 30 women — read at source, appraised in full.
−10.7%
Skin pigment in 10 weeks
Melanin index on the glutathione side of the face, from 272.8 to 243.5, against −3.1% on the placebo side (p < 0.001), read by a Mexameter probe (Watanabe et al., 2014).
77%
Saw moderately brighter-looking skin by week 10
The women's own ratings at week 10: the glutathione side moderately brighter for 77%, the placebo side for 23%. The investigator's ratings: 67% against 3%.
87% vs 10%
Rated at least a little brighter by week 6
At week 6, both the investigator and the women themselves rated 87% of glutathione sides at least a little brighter, against 10% of placebo sides. Pigment itself was already lower on the glutathione side at week 1 (p < 0.05), and at p < 0.001 every week from week 3.
Original research by Watanabe F, Hashizume E, Chan GP and Kamimura A, published in Clinical, Cosmetic and Investigational Dermatology (2014).
Appraised by the Skingenetix research team. Medically reviewed by Dr Esther Bodde, Cosmetic & Medical Physician. Last reviewed 30 September 2026.
Glutathione is an antioxidant the body makes in its own cells: a peptide of three amino acids, glutamate, cysteine and glycine. Skincare uses it for brighter-looking skin. This trial used its oxidised form, GSSG (two glutathione molecules joined together), which breaks down less easily in water than the reduced form.
The Watanabe 2014 trial is a randomised, double-blind, split-face study in which 30 women aged 30 to 50 applied a 2% oxidised glutathione lotion to one side of the face and a placebo lotion to the other, twice a day. After 10 weeks the glutathione side had brighter-looking skin: its melanin index fell 10.7%, against 3.1% with placebo (p < 0.001).
Our verdict: still the only placebo-controlled trial of oxidised glutathione on its own on skin, and a clear result: lower skin pigment than placebo from the first week, and brighter-looking skin that most of the women could see by week 10. It was run by Kyowa Hakko Bio, which makes the ingredient, in 30 women with skin types III and IV, so we cite it for the ingredient as studied.
At a glance
The nine things worth knowing before you weigh what this trial found.
Randomised, double-blind, placebo-controlled split-face trial: glutathione on one side of each face, placebo on the other, the side chosen at random.
30 healthy Filipino women aged 30 to 50 (average 36.1), skin types III and IV, all with uniform skin colour, chosen from 80 volunteers for having almost the same pigment level on both cheeks.
About 0.5 g of a lotion with 2% oxidised glutathione (GSSG), twice a day, on one side of the face, with no other skincare or make-up on the test areas.
A matching lotion without GSSG, at the same pH (6.46), on the other side of the same face. Neither the women nor the investigator knew which side had which.
10 weeks, with instrument readings every week and ratings every two weeks.
Mexameter (pigment) and Corneometer (moisture) on the cheekbone; image analysis of the crow's feet for wrinkles and texture; a Triplesense sensor for elasticity; ratings of visible change by the investigator and each woman.
2% oxidised glutathione (GSSG) by weight, stated in the methods and Table 1: 2 g in every 100 g of lotion.
Run by Kyowa Hakko Bio, which makes GSSG and supplied it; three of the four authors worked there. No outside funding; the paper declares no conflicts of interest. Carried out at a clinical testing company in the Philippines.
A− — randomised, double-blind and placebo-controlled, measured by instrument and by blinded ratings; but small, and run by the ingredient's maker, which employed three of the four authors.
What the measurements showed
Skin pigment at the start and at week 10
Melanin index on each cheekbone, read by a Mexameter probe. Lower means less pigment: skin that looks brighter.
2% glutathione sidePlacebo side
Start
Week 10
| Melanin index | 2% glutathione side | Placebo side |
|---|---|---|
| Start | 272.8 | 274.1 |
| Week 10 | 243.5 | 265.5 |
The two sides started level, 272.8 and 274.1. By week 10 the glutathione side had fallen 10.7% and the placebo side 3.1%; the difference was significant from week 1 and at p < 0.001 from week 3 onwards (Watanabe et al., 2014, Figure 2). The women's own ratings are in the key figures above.
What the researchers did
The researchers screened 80 healthy Filipino women and chose 30, aged 30 to 50, whose two cheeks held almost the same amount of pigment. Each woman received two lotions, one with 2% oxidised glutathione and one without, and the side of the face for each was chosen at random. Neither she nor the investigator knew which was which.
Twice a day for ten weeks, after washing, the women spread about half a gram of each lotion on its side of the face. They were asked to keep out of the sun and to use no other skincare or make-up on the test areas. Pigment and moisture were read on the cheekbone every week, and the crow's feet beside each eye were photographed and analysed.
How to read this result
- What the headline figure measures. The melanin index is a probe reading of the pigment in the skin, taken on the cheekbone. The glutathione side read lower than the placebo side every week; the percentages are our arithmetic from the paper's means.
- What "brighter" means here. Every woman started with uniform skin colour, so the result is about the overall look of the cheek: lower pigment, brighter-looking skin. The authors define the "moderate" change that 77% of the women saw as "perceptible and visible", with a change of less than 50% in skin colour: a gradual shift, not a new complexion.
- Crow's feet. A third of the women were rated visibly softer on the glutathione side at week 10 (by the investigator 33%, by the women 30%, on placebo 0%). By image analysis the wrinkle reading was significantly lower on the glutathione side than on the placebo side at weeks 6 and 10.
- Texture and moisture. Instruments recorded smoother texture from week 6 and more moisture at weeks 8 and 9 (p < 0.05) on the glutathione side.
- Scale and sponsor. 30 healthy Filipino women with skin types III and IV, asked to avoid the sun and using no sunscreen; men and other skin types were not studied. Kyowa Hakko Bio, which makes GSSG, supplied it and employed three of the four authors; the paper declares no conflicts of interest.
- Tolerability. All 30 women completed the trial. One had mild redness over her whole face on days 2 and 3, gone by day 4 without stopping; no reaction was linked to glutathione. The authors call for more study of longer use.
Where this trial sits in the evidence
Much of the research on glutathione and skin tests supplements taken by mouth, which cannot speak for a lotion. Reviews of topical glutathione rely on this trial: an academic systematic review concluded that "topical 2.0% oxidized glutathione could brighten skin color in sun-exposed area" (Dilokthornsakul et al., 2019).
An independent double-blind trial points the same way: 46 women used a glutathione and vitamin C serum on one cheek and a placebo serum on the other for 8 weeks, and the authors concluded that topical glutathione was effective (Wahab et al., 2021). With vitamin C in the serum, it supports this result's direction, not its numbers.
Every study we rely on, graded, is on the glutathione evidence hub, beside our other ingredient research. The Clinical studies list gathers every trial we have appraised, including the copper peptide trial.
Common questions about this trial
Does this trial prove the ingredient works?
It is the strongest evidence that glutathione applied to the skin brightens its look: skin pigment fell 10.7% in 10 weeks against 3.1% with placebo (p < 0.001), and 77% of the women saw brighter-looking skin on the treated side, against 23%. It is one maker-run trial of 30 women; an independent serum trial points the same way, and the rest is on the glutathione evidence hub.
What concentration did the study use?
2% oxidised glutathione (GSSG) by weight, or 20,000 parts per million, in a simple lotion at pH 6.46. About 0.5 g, a coin-sized amount, went on each side of the face twice a day. The GSSG came from Kyowa Hakko Bio.
Is the trial independent?
No. It was run by Kyowa Hakko Bio, which makes GSSG: three of the four authors worked there, the company supplied the ingredient, and there was no outside funding. The paper declares no conflicts of interest. It was carried out at a clinical testing company in the Philippines, with ethics committee approval, and published in the peer-reviewed journal Clinical, Cosmetic and Investigational Dermatology.
Do Skingenetix products reproduce this result?
No study has tested our serum. Our Glutathione 2% Brightening Serum is a different formula from the trial's simple lotion: it pairs glutathione with a vitamin C derivative, niacinamide and peptides. So the trial's results are not our serum's results; we cite the trial as evidence for the ingredient as studied.
Before you try it
This article summarises one published study. It is not medical advice, and your own results may differ. Our products are cosmetics. As with anything new for your skin, try a small amount on your inner forearm for 24 hours first, and add one new product at a time. Stop using it if you notice redness, itching, burning or swelling. If irritation continues, or if you have a skin condition, are pregnant or breastfeeding, or use prescription skin treatments, please ask your doctor or pharmacist before starting.
What it means for our products
This trial is why glutathione is in our range for brighter-looking skin: applied twice a day, the oxidised form lowered skin pigment against placebo from the first week, and it was well tolerated.
Our Glutathione 2% Brightening Serum is a different formula from the trial's lotion, so we cite the trial for the ingredient as studied, not as a result our serum has repeated. Use it morning and evening for at least ten weeks, the length of the trial, with sunscreen in the morning. The rest of the evidence is on the glutathione research hub.
Reference
Watanabe F, Hashizume E, Chan GP, Kamimura A. Skin-whitening and skin-condition-improving effects of topical oxidized glutathione: a double-blind and placebo-controlled clinical trial in healthy women. Clinical, Cosmetic and Investigational Dermatology 2014;7:267–274. doi:10.2147/CCID.S68424
Read at source: the full text on PubMed Central, 30 September 2026. Figures on this page come from the methods, the results, Tables 1 to 3 and Figures 2 and 3, not the abstract. The percentage changes in the melanin index are our arithmetic from the paper's means.