Potassium Methoxysalicylate God Antioxidant Reducerer mørke pletter Potassium Methoxysalicylate at a glance Derivative of salicylic acid Fights dark spots Originally developed by Shiseido Also known as 4MSK Potassium Methoxysalicylate description Potassium methoxysalicylate, also known as potassium 4-methoxysalicylate and by the trade name 4MSK, is a synthetic salicylic acid derivative. Originally developed by Japanese cosmetics brand Shiseido, it is now gaining wider use in skin care formulations. Despite its association with salicylic acid, potassium methoxysalicylate does not exert strong keratolytic (exfoliating) properties on skin because the potassium component keeps the acid outside the pH range it needs to exfoliate. Instead, where this ingredient shines most is in its ability to fight dark spots and brown patches. It does this by inhibiting tyrosinase, an enzyme associated with melanin overproduction. While most of the existing research is done by scientists with or for Shiseido, there is independent research indicating potassium methoxysalicylate’s efficacy in this area. Usage levels of potassium methoxysalicylate in cosmetics preparations generally range from 3-5%. Related ingredients: Salicylic Acid