Final answer:
Serums and ampoules containing active ingredients like peptides and antioxidants are best applied under a moisturizer to ensure deeper penetration and effectiveness, as moisturizers help to seal in these actives and prevent water loss.
Step-by-step explanation:
Serums and ampoules are designed to be applied under a moisturizer, mask, or massage cream because they contain active ingredients that are best absorbed when sealed in by an occlusive layer. These actives, such as peptides and antioxidants, can then work more effectively to hydrate, repair, and protect the skin. Moisturizers may contain occlusives that form a barrier on the skin to prevent water loss, and humectants which draw moisture into the skin. The layer of moisturizer acts as a seal over the serum or ampoule, allowing the active ingredients to penetrate more deeply and efficiently rather than being evaporated away.
Moreover, moisturizers modify the rate of water loss from the skin. Some moisturizing products contain anti-inflammatory ingredients that can help alleviate itching and inflammation, and also include other beneficial substances like ceramides and emulsifiers. By applying serums and ampoules under a moisturizer, the effectiveness of these products is enhanced, as they are better able to deliver their hydrating and anti-aging benefits to the skin.