C peptide is a biomarker for beta cell function. In other words, it's a measure of beta cell health and insulin production, and is critical to developing new disease modifying therapies for type 1 Combining Salicylic, Lactic, and Glycolic acids with Vitamin C Skin Beauty How To Use Salicylic Acid With Other Skincare Ingredients R49 Glutathione Peel for Chemical Peeling. Professional Use 30ml Glutathione 15%, Glycolic 25%, Kojic 15%, Lactic 10%, Salicylic 2% Rejsol