When we talk about serums and essences, the difference between them is very blurry… Once it was considered that essences are much lighter in texture and have less concentration and amount of active ingredients in them than those in serums. But as for nowadays this difference is not that obvious. Serums are made lighter in texture and essences become thicker, and as to the concentration of active ingredients – it depends more on the brand, the product itself and the skin problem/s it is meant to solve.
In Korean skincare routine both products are recommended to use at the same step – after toner and before moisturizer – but it should be or serum or essence and never both of them together. Which also proves, that they are if not completely the same kind of product, then certainly very close ones.
And even more than that, these names - "serum" and "essence" – sometimes look more of a marketing move. No, none is trying to cheat you, but for the manufacturers it is known, that the product with high level of active ingredients is more familiar to the western women under the name "serum", and for the Asian women under the name "essence". And because of this difference in perception, they try to name their products accordingly to their main target audience.
Now, when we made it more or less clear about serums and essences, let's move to ampoules.
This product sometimes might come in the form of real ampoules, but mostly it has just a regular form of liquid/creamy/jelly substance in a jar. Then why it is an ampoule? Because it has a VERY high concentration of ingredients which are aimed to fight a very certain skin problem. The concentration is even higher than this in serums and essences, and unlike them, which you can use as a part of your daily skincare routine on a constant basis and for a very long time – ampoules are applied by courses, only for some period of time when your skin needs an additional help/nutrition/recovery. It does remind some kind of medical treatment, and probably that's where the name "ampoule" comes from.
It is a great product, but using it just keep in mind, that it is a very strong product and it is better to introduce it to your skin by applying a very small amount in the beginning and carefully watching your skin reaction to it.
What is the right place of ampoule in Korean skincare routine? Some say right after toner before serum/essence, some say after serum/essence and before moisturizer… We'd say – read carefully the manufacturer's recommendations and directions of use and follow them (and that is also the right way to do with serums and essences!). And again – watch carefully your skin reactions (in the end – it is all matter of personal preferences and individual perception of the products by your skin).