How do moisturizers work?

     The term “Moisturizer” is a generic term used to describe a multitude of skin care product formulations that vary in their ability to hydrate the skin, improve skin health, and improve the aesthetic appearance of the skin. Moisturizers sold in the marketplace today can be classified into four main types based on their ingredients:

  • Occlusive based – These oily substances block water evaporation by providing a film on the skin’s surface and thereby trapping water in the upper most layer of skin, the stratum corneum. The most common occlusive ingredients include petrolatum, mineral oil, vegetable oil, and cetyl alcohol. Although very effective in sealing the skin’s surface, these ingredients are often sticky and greasy, and therefore, less cosmetically appealing. Oil-free occlusives, like silicone and its derivatives: dimethicone, cyclomethicone, and amodimethicone, are also commonly found in these moisturizers. The increase in skin hydration from the use of these occlusive agents hydrates dry and damaged skin, and results in increased skin smoothness and an improvement in barrier repair.
  • Humectant based – Moisturizers containing these ingredients work by attracting water from below the epidermis and from the atmosphere, and drawing it into the stratum corneum. Common humectants include glycerin, urea, pyrrolidone carboxylic acid (PCA), lactic acid, propylene glycol, sorbitol and vitamins. Most often intended for daily use on normal skin, these moisturizers are usually water based and very aesthetically pleasing.
  • Emollients – Moisturizers that contain emollients are designed to make the skin feel soft and appear smooth. These products often provide fragrance rather than increase hydration. Emollient based moisturizers are suitable for daily use on normal skin. Emollients are often lipids and oils that soften the skin and impart a smooth and silky feel. Although emollients are less effective at sealing the skin’s surface from water loss than occlusives, they do have some occlusive ability, and therefore, can improve the appearance of dry flaky skin. Common emollients found in moisturizers include lanolin, cetearyl alcohol and sunflower seed oil.
  • Therapeutic Moisturizers – These formulations are designed to treat dry, damaged, and diseased skin conditions. They contain occlusives for water barrier effects, humectants to draw water into the stratum corneum, and emollients to soften the skin. These moisturizers often contain compounds found in the Natural Moisturizing Factor (NMF) like urea, lactic acid, and/or pyrrolidone carboxylic acid (PCA). In addition, they often contain lipids that mimic those found in the stratum corneum, such as ceramides.  

     Emollient based and Humectant based moisturizers may temporarily improve the appearance of dry skin, but they do very little to repair the skin’s barrier function. Occlusive based and Therapeutic moisturizers are more effective in decreasing water loss through the skin by improving the skin’s ability to hydrate.