Thiamidol
Synthetic tyrosinase inhibitor, INCI Isobutylamido Thiazolyl Resorcinol. In melasma RCTs mMASI fell more than with vehicle, but instrumental color readings did not differ and the effect faded after stopping
Evidence by route
Topical application
Melasma and facial hyperpigmentation have the best data. In several RCTs, including independent ones, pigmentation on clinical scales decreased more than with vehicle or hyaluronic acid and did not differ from 4% hydroquinone. Instrumental color readings did not differ from vehicle, and the effect faded within 13–20 weeks after stopping. Data on post-acne marks are weaker. Lentigines and freckles did not lighten more than with vehicle, and there are no comparisons with azelaic acid
- B
Brightening
In several RCTs, including independent ones, melasma mMASI fell more than with the control (−36.1% vs −16.1% with vehicle at 12 weeks), but instrumental color readings did not differ from vehicle
- B
Post-acne marks and post-inflammatory pigmentation
In the manufacturer's vehicle-controlled RCT on post-acne marks, only self-assessment differed. In an independent RCT, applying it before laser lowered the rate of post-inflammatory pigmentation (20.8% vs 50%) without instrumental differences
- D
Comparison with 20% azelaic acid
No published study has compared thiamidol directly with azelaic acid
- D
Solar lentigines and freckles
In a vehicle-controlled RCT of 200 people, freckles and solar lentigines did not lighten more than with vehicle; positive data come only from the manufacturer's uncontrolled observation
- Lima PB et al. Efficacy and safety of topical isobutylamido thiazolyl resorcinol (Thiamidol) vs. 4% hydroquinone cream for facial melasma: an evaluator-blinded, randomized controlled trial. J Eur Acad Dermatol Venereol. 2021;35(9):1881-1887. PMID 33988887
- Disphanurat W et al. Efficacy and safety of 0.15% isobutylamido thiazolyl resorcinol combined with hyaluronic acid vs 0.15% isobutylamido thiazolyl resorcinol or hyaluronic acid alone in melasma treatment: A randomized evaluator-blind trial. J Cosmet Dermatol. 2021;20(11):3563-3572. PMID 33638926
- Vachiramon V et al. Combined isobutylamido thiazolyl resorcinol and low-fluence Q-switched Nd: YAG laser for the treatment of facial hyperpigmentation: A randomized, split-face study. J Cosmet Dermatol. 2021;20(6):1724-1731. PMID 33118677
- Roggenkamp D et al. Thiamidol(®) in moderate-to-severe melasma: 24-week, randomized, double-blind, vehicle-controlled clinical study with subsequent regression phase. J Dermatol. 2021;48(12):1871-1876. PMID 34676600
- Lekhavat C et al. Efficacy and Tolerability of 0.2% Thiamidol Cream for Facial Hyperpigmentation: A Randomized, Double-Blind, and Vehicle-Controlled Study. Dermatol Ther (Heidelb). 2026;16(3):1551-1565. PMID 41566113
- Arrowitz C et al. Effective Tyrosinase Inhibition by Thiamidol Results in Significant Improvement of Mild to Moderate Melasma. J Invest Dermatol. 2019;139(8):1691-1698.e6. PMID 30825454
- Roggenkamp D et al. Effective reduction of post-inflammatory hyperpigmentation with the tyrosinase inhibitor isobutylamido-thiazolyl-resorcinol (Thiamidol). Int J Cosmet Sci. 2021;43(3):292-301. PMID 33559186
- Vachiramon V et al. Efficacy of isobutylamido thiazolyl resorcinol for prevention of laser-induced post-inflammatory hyperpigmentation: A randomized, controlled trial. J Cosmet Dermatol. 2024;23(7):2450-2457. PMID 38497328
- Mann T et al. Inhibition of Human Tyrosinase Requires Molecular Motifs Distinctively Different from Mushroom Tyrosinase. J Invest Dermatol. 2018;138(7):1601-1608. PMID 29427586
- Vachiramon V et al. Isobutylamido thiazolyl resorcinol for prevention of UVB-induced hyperpigmentation. J Cosmet Dermatol. 2021;20(3):987-992. PMID 32757247
- Klein PA et al. Isobutylamido Thiazolyl Resorcinol (Thiamidol) for Combatting Hyperpigmentation: A Systematic Review of Clinical Studies. J Drugs Dermatol. 2024;23(11):986-991. PMID 39496126
- Sarkar R et al. Thiamidol in Melasma in Patients of Skin of Color: A Preliminary Report of Efficacy and Safety. Indian Dermatol Online J. 2025;16(5):760-764. PMID 40847672
- Vernhet L et al. First Two Cases of Allergic Contact Dermatitis From Isobutylamido Thiazolyl Resorcinol ('Thiamidol') in Depigmenting Skin Care Routine. Contact Dermatitis. 2025;93(1):63-65. PMID 40143431
- Sukakul T et al. Allergic Contact Dermatitis to Isobutylamido Thiazolyl Resorcinol (Thiamidol). Contact Dermatitis. 2025;93(3):260-262. PMID 40456229
- Erler S et al. Targeting Melanin Production: The Safety of Tyrosinase Inhibition. Int J Mol Sci. 2025;27(1). PMID 41515976
How to read tiers A–F
- BLimited evidence. One RCT or several controlled studies with limitations
- DNo data, or very weak or conflicting data
Tolerability and safety
- Working concentrations
- An independent RCT found an effect on mMASI with 0.15% (Disphanurat 2021); most RCTs used 0.2%. A systematic review describes 0.1–0.2% applied 2–4 times a day for 12–24 weeks (Klein 2024)
- Irritation potential
- Low
- Allergen risk
- Moderate
- Pregnancy
- Caution
- Suitable for
- Normal, Oily, Combination, Dry, Sensitive
About this ingredient
Thiamidol is the trade name of isobutylamido thiazolyl resorcinol, a synthetic tyrosinase inhibitor. A cosmetics company patented it and ran or funded many of the studies. In the developer's tests on recombinant human tyrosinase, the IC50 of thiamidol was 1.1 μmol/L. For kojic acid it was above 500 μmol/L, and for hydroquinone it was in the millimolar range. In melanocyte cultures it suppressed melanin production reversibly (Mann 2018). These tests did not measure any effect on skin. It is used in creams and serums for melasma and other facial dark spots; trials tested 0.15–0.2%. The manufacturer funded a vehicle-controlled RCT of 200 people (Lekhavat 2026). Over 12 weeks, mMASI fell by 36.1% with 0.2% cream and by 16.1% with vehicle, but digital color analysis showed no difference between groups. In a 24-week manufacturer trial, skin lightness did not differ from vehicle either, and 13–20 weeks after stopping, MASI was the same in both groups (Roggenkamp 2021). An independent RCT found no difference from 4% hydroquinone (Lima 2021). In another independent RCT, mMASI at week 12 was lower with 0.15% than with hyaluronic acid (Disphanurat 2021). In the Lima 2021 RCT, 2 of 25 women using thiamidol developed allergic contact dermatitis, and later reports describe more cases (Vernhet 2025, Sukakul 2025). There are no data on use during pregnancy and breastfeeding.
Frequently asked questions
Is Thiamidol safe during pregnancy?
Thiamidol should be used with caution during pregnancy. Consulting a dermatologist or OB-GYN is advisable.
What skin types is Thiamidol for?
Thiamidol suits: normal, oily, combination, dry, sensitive.
What is Thiamidol and what does it do in cosmetics?
Synthetic tyrosinase inhibitor, INCI Isobutylamido Thiazolyl Resorcinol.
What's the INCI name for Thiamidol?
The INCI name is Isobutylamido Thiazolyl Resorcinol. It may also appear as: Thiamidol.
What concentration of Thiamidol is effective?
An independent RCT found an effect on mMASI with 0.15% (Disphanurat 2021); most RCTs used 0.2%. A systematic review describes 0.1–0.2% applied 2–4 times a day for 12–24 weeks (Klein 2024)
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