I have always wondered about the formula for layering daily SPF application, and today's post on The Beauty Brains has give me the most comprehensive answer in years. This is generally a preference thing but I prefer to have separate SPF to my moisturiser as I find that generally the 2-in-1 tends to block my pores leading to a most annoying dry skin WITH spots!! Anyhoo, here is the comprehensive and concise description from the Beauty Brains: "For physical blocking sunscreens (minerals) like Titanium Dioxide or Zinc Oxide, it doesn’t matter. They’ll work just the same whether it’s put on first or last. In this case, we recommend putting it on after your moisturiser just so the sunscreen doesn’t inhibit the penetrating ability of the moisturiser (or other treatment). Chemical sunscreens (e.g. Oxycinnamate) are a bit different because the raw materials in the formulas can have an impact on the final SPF rating. That means if you use apply it after your moisturizer, you may reduce the SPF efficacy. So, Zinc & Titanium on last, all other sunscreens on first. Of course, you could actually solve the entire problem by using a moisturizer that contains sunscreen."