Cosmetics Formulation Development

I want to ask Vitamin CE Ferulic ready to use formula can be mixed Phenylethyl Resorcinol 0.5% and Ergothioneine Can you add 1%?

Hello, you can add it, but it's not recommended because it may affect your system. Vitamin C and make Vitamin C deteriorate faster? But if you add it for your own use And keep it in the refrigerator all the time. You can do it, no problem.