Hi Dr. Irwin, I am wondering about using a Vitamin C serum in the morning under my sunscreen. I have read on several places online (and had one aesthetician tell me) that Vitamin C breaks down in the sunlight. She said that your skin won't benefit from it if you wear it during the day under your sunscreen. I'm wondering if I should only use it at night? Thanks so much. I read your book and changed my skincare routine based on it, and I'm lovining your recommendations and the results! Wendy