Cosmetics · Quasi-drug actives
4-Methoxysalicylic Acid Potassium Salt
4-メトキシサリチル酸カリウム塩 (4-Metokishi sarichirusan kariumu en)
Also known as: Potassium Methoxysalicylate, Shiseido refers to this ingredient as 4MSK
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| Category | Cosmetics |
|---|---|
| INCI name | Potassium Methoxysalicylate↗ |
| Japanese labeling name | 4-メトキシサリチル酸カリウム塩 |
| Common Japanese notations | 4-メトキシサリチル酸カリウム塩, 4MSK |
| CAS number | 152312-71-5↗ |
| Origin | Synthetic (salicylic acid derivative) |
| Typical functions | Quasi-drug whitening (medicated bihaku) active |
| Regulatory status in Japan | Approved as a quasi-drug (医薬部外品) whitening active by Japan's 厚生労働省 (Ministry of Health, Labour and Welfare). Approval applied for by Shiseido and granted in 2003. |
4-Methoxysalicylic acid potassium salt is a salicylic acid derivative approved as a quasi-drug whitening active in Japan. Shiseido — the company that applied for the approval, granted in 2003 — refers to the ingredient using the abbreviation 4MSK across its Japanese-market communications. The ingredient is positioned around prevention of melanin-related hyperpigmentation, the standard regulatory claim wording for medicated whitening actives.
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Classification
Tags below link to other ingredients sharing the same attribute, so you can pivot from one ingredient to its peers.
Product applications
Functions
Regulatory tags
Origin
Common OEM product categories
Finished-product categories where Japanese OEM manufacturers commonly formulate with this ingredient.
- Medicated whitening serums (薬用美白美容液)
- Medicated whitening lotions and emulsions
- Quasi-drug skincare lines
- Spot-care treatment products
Ingredient profile
4-Methoxysalicylic acid potassium salt is the potassium salt of 4-methoxysalicylic acid, a synthetically produced salicylic acid derivative. Within the Japanese quasi-drug regulatory framework it is permitted as an approved active ingredient at concentrations defined by Shiseido's 厚生労働省 (Ministry of Health, Labour and Welfare) approval.
Quasi-drug status means the ingredient appears in the active ingredient (有効成分) section of finished-product ingredient lists, separate from the other ingredients (その他の成分).
OEM applications
Medicated whitening (薬用美白) lines, particularly those marketed by Shiseido. The ingredient appears in serums, lotions, and emulsions positioned around prevention of sun-induced spots.
Regulatory classification in Japan
Approved by 厚生労働省 (Ministry of Health, Labour and Welfare) as a quasi-drug whitening active in 2003 following an application by Shiseido. Permits the standard medicated-whitening claim wording: prevention of spots (シミ) and freckles (ソバカス) caused by sun exposure.
Regulatory classification in other markets
| EU | Listed in CosIng under Potassium Methoxysalicylate. Permitted for cosmetic use; not the subject of a quasi-drug-equivalent regulatory category in the EU. |
|---|---|
| USA | INCI Potassium Methoxysalicylate. Used in cosmetic products. |
| China | Verify the specific preparation against current IECIC listings. |
| Korea | Permitted for cosmetic use under KFDA / MFDS. |
Market reference formulations
Example finished products containing this ingredient are marketed primarily by Shiseido under various medicated whitening lines. Specific SKU listings will be added after each product's current full ingredient list has been verified.
All brand names and product names referenced anywhere on this site are the property of their respective owners. Example entries are provided for informational purposes only and do not imply endorsement.
Typical OEM use levels
Formulation ranges per finished-product application. Verify against the cited source before production.
| Application | Typical range | Regulatory limit | Notes |
|---|---|---|---|
| Quasi-drug whitening serum / lotion (Japan) | 1–3% | Set per individual 厚生労働省 quasi-drug notification | Marketed as 4MSK; trademarked formulations supplied by Shiseido and licensed brands(厚生労働省 医薬部外品有効成分通知) |
Stability & compatibility
- pH range
- pH 4.5–7.0
- Temperature
- Stable at standard cosmetic processing temperatures
- Incompatibilities
- Strong oxidizers
Potassium salt form is water-soluble; potassium salts of salicylates are generally stable in standard skincare bases.
Alternative ingredients
Related ingredients commonly evaluated as substitutes.
Quick answers
- What is 4-Methoxysalicylic Acid Potassium Salt?
- 4-Methoxysalicylic acid potassium salt is a salicylic acid derivative approved as a quasi-drug whitening active in Japan. Shiseido — the company that applied for the approval, granted in 2003 — refers to the ingredient using the abbreviation 4MSK across its Japanese-market communications. The ingredient is positioned around prevention of melanin-related hyperpigmentation, the standard regulatory claim wording for medicated whitening actives.
- What is the regulatory status of 4-Methoxysalicylic Acid Potassium Salt in Japan?
- Approved as a quasi-drug (医薬部外品) whitening active by Japan's 厚生労働省 (Ministry of Health, Labour and Welfare). Approval applied for by Shiseido and granted in 2003.
- What products typically use 4-Methoxysalicylic Acid Potassium Salt?
- Medicated whitening serums (薬用美白美容液) / Medicated whitening lotions and emulsions / Quasi-drug skincare lines / Spot-care treatment products
- Where does 4-Methoxysalicylic Acid Potassium Salt come from?
- Synthetic (salicylic acid derivative)
- What is the INCI / JSCI labeling name for 4-Methoxysalicylic Acid Potassium Salt?
- INCI: Potassium Methoxysalicylate / JSCI: 4-メトキシサリチル酸カリウム塩
Explore related ingredients
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Sharing similar functions
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From the same origin
Other ingredients that share an origin classification.
Regulatory guidance
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FAQ for OEM buyers
Q. What is the regulatory status of potassium methoxysalicylate in Japan?
It is approved as a quasi-drug (yakubu-gai-hin) whitening active by 厚生労働省 (Ministry of Health, Labour and Welfare) for prevention of sun-induced spots and freckles. Use in finished products requires quasi-drug application/notification, not just cosmetic notification.
Sources · Last reviewed: 2026-04-26
- 厚生労働省 (Ministry of Health, Labour and Welfare) — quasi-drug approval lists (medicated whitening actives)
Q. Can an overseas brand use this active in their own OEM line?
It is a Shiseido-developed active (commercial name 'm-tranexamic acid' / 'Methoxy'-positioned ingredient family was developed in-house), and supply outside Shiseido's group is restricted in practice. Most third-party OEMs cannot source it for non-Shiseido brands.
Sources · Last reviewed: 2026-04-26
- Industry knowledge — Shiseido proprietary actives
Industry-knowledge claim — not yet pinned to a single primary source
Q. What CAS number and INCI should be on the spec?
CAS 152312-71-5; INCI 'Potassium Methoxysalicylate'. Confirm spec sheet matches Japan-domestic 薬用美白 ingredient nomenclature.
Sources · Last reviewed: 2026-04-26
- PubChem CID — CAS 152312-71-5 (Potassium 4-Methoxysalicylate)
Q. What claim language is permitted in Japan with this active?
Quasi-drug whitening claims permit 'メラニンの生成を抑え、しみ・そばかすを防ぐ' (suppresses melanin formation; prevents sun-induced spots and freckles), but no broader anti-aging or treatment claims. Export markets need separate claim review (US FDA does not recognize Japanese whitening claims).
Sources · Last reviewed: 2026-04-26
- 厚生労働省 (Ministry of Health, Labour and Welfare) — Standards for permissible quasi-drug efficacy claims
Use cases
Medicated whitening serum (薬用美白美容液)
- Positioning
- Premium Shiseido-group whitening line
- Formulation notes
- Water-phase active in quasi-drug formulation; pH-stable in mildly acidic formulations.
Sources
- Industry knowledge — Shiseido medicated whitening line composition
Industry-knowledge claim — not yet pinned to a single primary source
Medicated whitening lotion / emulsion
- Positioning
- Daily-use whitening regimen
- Formulation notes
- Combined with other whitening actives (e.g., tranexamic acid, ascorbyl glucoside) within Shiseido group products.
Sources
- Industry knowledge — Shiseido whitening product lineup
Industry-knowledge claim — not yet pinned to a single primary source
Premium spot-care concentrate
- Positioning
- Targeted spot/dark-area treatment
- Formulation notes
- Higher-strength leave-on serum format; quasi-drug registration mandatory.
Sources
- Industry knowledge — premium spot-care category
Industry-knowledge claim — not yet pinned to a single primary source
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Official regulatory databases
External links to public Japanese / international regulatory authorities. We are not affiliated.
References
- Japan 医薬品医療機器総合機構 PMDA (Pharmaceuticals and Medical Devices Agency) — quasi-drug active ingredient approval registry
- Shiseido official corporate publications referencing 4MSK
Last updated: 2026-04-22. Ingredient entries are reviewed at least annually against current regulatory listings.