We all have heard of face serums and may even use a variety of face serums already, but what the heck are they are exactly used for? You are not alone in having no idea what a serum is. They can seem confusing... they're moisturizing, but you still need to use moisturizer. They can be oily, but it's not necessarily a face oil. Let's get down to the truth of serums. Here are the top three FAQs: