filling In small quantities, this can be done, but is only suitable for professionals. because they must be able to observe or test the changes In terms of the stability of the formula, yes, for example, if the formula changes color. It may indicate that the ingredients added to have an effect on the efficiency of Vitamin CPlease feel free to ask. It is unknown whether these substances can be added to Natural-C Glycol you please 1. Double Hyaluron moisturizing ic 2. Group ลดการระคายเคือง