“A moisturizer’s job is to reduce the amount of water that evaporates off of the skin to minimize transepidermal water loss. They lock in and seal in moisture,” explains Dr. Guanche. Moisturizing is particularly helpful for skin that is dry and peeling or flaking after undergoing a chemical peel, using Retin-A or during the winter, according to Dr. Guanche, a Los Angeles dermatologist.  Essentially, moisturizers differ from serums in that they function as a Barrier to keep moist in.