Derived from Korean beauty practices, the incorporation of essences, ampoules and emulsions into a skincare regimen places a strong emphasis on hydrating the skin. Containing higher concentration of active ingredients than serums and moisturisers, these products are water-based formulas aimed to be light enough to sink deeper into the skin, treating skin conditions on a cellular level — resulting in flawless skin as popularised in K-beauty culture. To get you started, here’s a quick guide to the differences between essences, ampoules and emulsions.
Essences
Although essences are less concentrated than serums, they do contain more hydrating ingredients that essentially soften the skin with an extra dose of hydration. This then allows the dermis to absorb the products in preparation for the next steps of your skincare routine and allowing it to reap more benefits from the overall beauty regiment and stay nourished.
How to use it: After washing and toning the face, pour a little essence into the palm of the hands and pat into the skin. Leave it to soak in for a minute or two before applying serum. 
Ampoule
Very much like serums, an ampoule commonly refers to a booster for the skin. Highly concentrated with active ingredients (often botanical in nature), not only does it hydrate the skin on a surface level, it also treats skin conditions such as ageing and brightening on a cellular level.
How to use it: Apply an ampoule after putting on serum. The product can even be mixed in with your moisturiser or foundation to keep the skin nourished while underneath thick layers of cream.
Emulsion
An emulsion is a light-weight watered down version of a facial lotion. It hydrates and moisturises the skin. Its water-based formula also makes layering other products afterwards more effective. They can also be applied underneath a sunscreen, and for those with oily skin types and aren’t fond of the heavy, thick or oily textures of face creams, emulsions are lighter and more breathable on the dermis, and therefore more comfortable to wear.
How to use it: Emulsions would typically go after toner, essence, serum, and ampoules (in that order), and just before a moisturiser because it is thinner in texture than a cream, but thicker and less concentrated than a serum or essence.