Types of moisturizers: Summary from the Nolan and Marmur paper
Posted on September 21 2017
This paper is a must read if you are interested in skin care and want to know the difference between common skincare terms such as occlusives, humectants, emollients, rejuvenators, ceramides and so on. Just a heads up -- we do not use petrolactum or dimethicone in our products. These ingredients and their efficacy are mentioned in the paper in great detail.
We have tried to summarize the paper in this blog post. The paper refers to the types of moisturizers and not a full product that is called moisturizer.
Our skin barrier has the ability to retain moisture and protect our internal tissues from infection, chemicals, and mechanical stress. Stratum corneum, or the outermost layer of the skin, does this job pretty well and is composed of anucleate corneocytes. It provides an effective barrier to water loss, although the skin does lose water anyway. This water loss, otherwise known as transepidermal water loss (TEWL) is low in healthy skin, but is interestingly often higher in people with conditions like eczema, dry skin, or psoriasis etc.
The most important element of skincare ingredients are the moisturizing elements. Whether they aim to address anti-aging, anti-wrinkle, etc, moisturizers play a critical role in the desired outcomes of these products. The efficacy of any moisturizer is in fact measured by its ability to reduce TEWL. Some type of moisturizers are:
Types of moisturizers
The dictionary meaning of occlusive is to serving to occlude or block off. Occlusives work by forming a water repellant layer on the skin and providing a seal to reduce TEWL. It is effective when applied to damp skin like applying a cream after your shower. Occlusives by nature are greasy but it reduces TEWL by 99% and is an effective remedy for dry skin or atopic dermatitis.
The role of humectants is to increase the water content of the skin by attracting moisture from the external environment. It also enhances the water absorption from the dermis into the epidermis. Humectants' hydroscopic properties enable them to attract and hold water molecules. If the skin barrier is compromised, humectants can cause water loss and therefore, humectants need to be combined with the occlusive to provide the external seal.
The most common humectant is glycerin and has the distinctive characteristic of enabling moisturizing effects in the skin long after it is no longer present.
Emollients are used to improve the appearance and texture of skin by filling in the crevices between corneocytes. Essential fatty acids such as Omega 3 and Omega 6 are examples of emollients and contributes to the softness and smoothness of the skin.
Rejuvenators are used to replenish essential proteins in this skin. Collagen, keratin, and elastin are skin proteins that are often found in rejuvenators. Proteins by nature are larger molecules and the challenge is to get them to penetrate the stratum corneum.
Ceramides are lipid molecules and are used in skin creams, lotions, eye creams etc. They are quite effective in the treatment of dry skin. Ceramides are naturally present in the skin and they are like the "mortar" in the skin building block analogy holding the "bricks" of the skin in the analogy.
Nolan, K, and E Marmur. “Moisturizers: Reality and the Skin Benefits.” Advances in Pediatrics., U.S. National Library of Medicine, www.ncbi.nlm.nih.gov/pubmed/22913439.