Serums are usually packed with very concentrated ingredients that target a particular skin concern. Drop a few drops on your face and massage gently to help your skin absorb the product.
You can use serums depending on which one and that product’s instructions say. It can usually be used morning and nights, but it’s better to use them in the evening to give them all their time to do their job perfectly.
The serums are usually referred to as ampoules or treatments.