Most “moisturizing” cream does not actually contain much water–it’s usually mostly fats or petroleum products. Instead, “moisturizers” contain humectants, chemicals which encourage your body’s cells to hold onto more liquid, and emollients, which are compounds that make skin feel softer and smoother. You also have occlusives, which work by creating a barrier that doesn’t allow moisture to escape.
So, in simple terms, moisturizers work by putting compounds into your skin that make the skin cells draw in more water, block the water the cells have from evaporating away, and make skin feel nice. Different preparations are an effort to try to capture more of the evaporation-blocking power of petroleum jelly, without being as supremely greasy.
Very little science is done on these claims, and whatever any given company does or makes is almost always a deeply-held proprietary secret.
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