Feel free to ask questions about using the serum. If using a serum with
Niacinamide 10% is the first bottle of serum. and want to use the second bottle of serum that is
L-ascorbic acid 10% can be used together or not? Recommend and how to use as well, for example, may leave a few minutes away from the first bottle of serum. or cannot be used together at all Thank you in advance