skin structure cosmetics
Article by: Kelly Dobos

Our skin has many important functions, including the prevention of water loss. Dry skin, or xerosis, is a common problem that many consumers seek to treat with cosmetic moisturizers. Whether for the face, hands, feet, or entire body moisturizer formulations are an important part of any cosmetic chemist’s tool kit.

Skin Structure

First, let’s talk a little about the structure of your skin. The upper layer of the skin, the epidermis, is further subdivided into four distinct layers. These layers from bottom to top are the stratum basale, the stratum spinosum, stratum granulosum, and the stratum corneum. There presence of a fifth layer, the stratum lucidum, can be seen in thicker areas of the epidermis like the soles of your feet. skin structure cosmetics

Keratinocytes, the main type of cells in the epidermis, migrate up from the dermis and undergo many changes to become a flat, keratin rich corneocyte before being shed. During this progression through the layers of the epidermis, lipids are released into the spaces between cells and the skin’s own natural moisturizing factor (NMF) is generated. These lipids form a barrier to water loss and help retain the skin’s NMF. Disruption of this lipid matrix and subsequent loss of hydration can lead to dry, flaky skin.1, 2

Cosmetic moisturizers are used to help repair the lipid barrier and restore hydration.

How cosmetic moisturizers work

Although there are some more specialized approaches, like the use of alpha-hydroxy acids or quaternary conditioning agents, most cosmetic moisturizers improve the condition of dry skin by utilizing one of three major ingredient types including

  1. Humectants
  2. Emollients
  3. Occlusive agents.


Humectants include ingredients like glycerin, urea, and pyrrolidone carboxylic acid (PCA). Humectants work by attracting water from the dermis below and helping to keep that water bound in the stratum corneum. Glycerin is used frequently because of its low cost and high efficacy, but a tacky feel on the skin is one of the drawbacks of formulating with high levels of humectants. When optimizing skin formulations, cosmetic chemists try to reduce these negative properties of humectants.

Occlusive Agents

Occlusive agents increase moisture levels by providing a physical barrier to epidermal water loss. Ingredients with occlusive properties include petrolatum, waxes, oils, and silicones. Some occlusive agents like petrolatum can leave a heavy feel so they are often combined with other ingredients, like emollients, to improve consumer appeal.


Emollients provide some occlusivity and improve the appearance of the skin by smoothing flaky skin cells. There are many different types of emollient esters and oils available to a formulation chemist3,4 Emollients are generally grouped by their ability to spread on the skin. By combining emollients with the different spread rates you can tailor the skin feel of a moisturizer. You can test for these differences by using different emollients in a standard base lotion. Additionally, emollient lipids similar to those naturally found in the skin may also increase the rate of barrier repair. 5

Putting it together

Each of these ingredient types has a different mechanism of action and most cosmetic moisturizers will use a combination of these ingredients to create a synergistic effect and mitigate certain aesthetic or financial drawbacks. Product claims and skin feel are also considerations to be aware of, so don’t be afraid to experiment with your options when creating a moisturizer. For tips on creating successful skin formulations, see our previous article on HLB formulating.


1. Harding CR; The Stratum Corneum: Structure and Function in Health and Disease, Dermatologic Therapy; 2004. Vol. 17, pp 6 -15.

2. Wickett RR, Visscher MO; Structure and Function of the Epidermal Barrier,
American Journal of Infection Control, 2006. Vol. 34, Issue 10, pp S98 – S110.

3. Flynn TC, Petros J, Clark RE, Viehman GE; Dry Skin and Moisturizers, Clinics in Dermatology, 2001. Vol. 19, pp 387 – 392.

4. Rawlings AV, Canestrari DA, Dobkowski B; Moisturizer Technology versus Clinical Performance. Dermatologic Therapy; 2004. Vol. 17, pp 49 – 56.

5. Mao-Qiang M, Brown BE, Wu-Pong S, Feinglod KR, Elias PM; Exogenous Non-physiologic vs. Physiological Lipids. Divergent Mechanisms for Correction of Permeability Barrier Dysfunction. Archives of Dermatology, 1995. Vol. 131, pp 809 – 816



  1. Avatar
    Wendy C.

    Hi Kelly,

    Thanks for this informative post. I am just using skin care products not know how these things work on the skin. I really don’t know that each has a mechanism of actions when applying moisturizers. Can’t wait to experiment with something new making DIY moisturizers. Thanks!

  2. Avatar

    Thank you for your breakdown of how moisturizers work. I was only aware of the importance and value of humectants. You have given me a totally new perspective when choosing moisturizers for my skin type. I will now start reading the ingredients for my moisturizers.

  3. Avatar

    Hi Kelly,

    I love moisturizers and what it does to my skin. Your article gave me an understanding of skincare in a deeper perspective. Thanks for sharing!

  4. Avatar

    Could you review hydraulic acid use in skin care product?

  5. Avatar

    I would like to know…that many people put many vitamin e in creams..does this vitamin e gets into our body through pores..

    1. Avatar
      Perry Romanowski

      No. It is unlikely that topical vitamin E gets significantly into skin.

  6. Avatar

    Skin is one of the largest organs in human body and serves as a protective barrier to external noxious agents including microorganisms.So,It is very important to study on the skin care.

  7. Avatar

    This information is very usefull, i used it to revise for my exams! very easy to understand and i find it very accurate. Thank you

  8. Avatar
    Science Girl

    This is very inaccurate.. including the layers of the skin from bottom to top. I didn’t even read any further.. wow.

    1. Avatar

      The information in this post is well established by numerous research papers.

    2. Kelly

      You should consider reading the cited papers which back up my information. If you have documentation of something different, I would be interested to see it. While constructive criticism is always appreciated, there is no need to be disrespectful.

  9. Avatar

    Do you know if ingredients to give a “dry fisnish” for the formula, like silica, Nylon-12 etc. will reduce the moisturizer efficacy?

    1. Avatar

      No, they really shouldn’t reduce moisturization but it depends on how much you put in and what kind of moisturizer you are using.

  10. Avatar

    Your diagram is wrong. The dermis is below the basal cell layer.

    1. Avatar

      I just saw the picture and I noticed that the dermis label were put in the wrong place..
      It should be put in the dense irregular connective tissue bellow the basal layer (stratum germinativum of epidermis)..

  11. Kelly

    Thank you for your complements Jennifer! A book titled Antiaging: Physiology to Formulation is a good resource available from Allured Publishing, it is a bit pricey but worth it because it compiles a lot of information that you would have find in individual pieces elsewhere. -Kelly

  12. Avatar
    Jennifer Skin Care Therapist

    Thanks so much Kelly for that information, as alot of companies say how bad mineral oil is. Very interesting information about Hylauronic Acid. I think this site is brilliant – I am so glad I found it! If you have one book to recommend to me about the latest skin care ingredients i.e. peptides etc, is there any particular ones you would recommend?

  13. Kelly

    Hi Jennifer,
    Thanks for your questions! Mineral oil is a cost-effective occlusive agent. However, there is widespread belief that mineral oil is comedogenic despite a good deal of data to the contrary (see article by DiNardo in Journal of Cosmetic Dermatology, 2005). There also exists some controversy regarding the fact that mineral oil is derived from petroleum, but it is a by-product of the distillation process and is an example of the utilization of a potential waste stream. Hyaluronic acid has powerful water binding capabilities within the skin as it is considered part of the skin’s own natural moisturizing factor (NMF). It is a very high molecular weight polymer which, I believe, would limit effectiveness in topical application because the molecule is just too big to penetrate the stratum corneum.

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