Skin absorbs lotion by drawing the material through the permeable outer layer of the skin, known as the epidermis. The amount of moisture already present in the skin, the duration of contact, and the physical condition and health of the skin determine the amount of lotion that is absorbed into the epidermis.
Between the skin cells of the epidermis are fats and lipids. Water soluble amino acids and salts in the skin help the cells retain moisture. The skin acts as a protective barrier against the elements and chemicals present in the environment, but its permeable surface may require moisturizer to keep it adequately hydrated. Natural enzymes that help to remove dead skin cells also need moisture in order to function properly.
The top layer of the epidermis is known as the stratum corneum, which determines the absorption of material put on the skin. It also regulates and prevents water loss from the deeper layers of the skin. The stratum corneum is thicker than other cell layers of the epidermis, which is made up of dead skin cells that are constantly being shed and renewed. Material rubbed into the skin is absorbed through the stratum corneum and into the bloodstream, including ingredients in the products being used, especially those contained in lotions that typically remain on the skin for a period of time.