Yes they can be used together. According to Paula Begoun, retinols dont exfoliate. They are a cell communicating ingredient and help with cell turn over. BHA's are a chemical exfoliant and are anti-inflammatory and anti- bacterial. Unlike AHA, BHA cleans out the pore. You use the BHA before the retinol product. Here's some info http://www.cosmeticscop.com/learn-skin-care-facts.aspx