Ampoules: These are designed to be used occasionally, such as when you need to address a specific skin concern quickly or when your routine needs a boost. Ampoules are highly concentrated with a key ingredient and may provide visible results faster than serums. They are often packaged in small glass vials and have a more runny texture than serums, so they are added to the face before serum or moisturizer. Not all ampoules are meant to be used in your daily skincare routine. 

Serum: These are typically designed to be suitable for daily use. Serums have a clear, gel-like, or liquid-based texture and often combine many different active ingredients, so you get the benefits of several at once, but in smaller concentrations. Serums are slightly more viscous than ampoules and should go into your routine after cleansing, but before moisturizing.