How do skin moisturizers actually work?

I was an average science student, honestly, but it always interested me. I have a proclivity for artistic expression, having a BA in Fine Arts and all, but have always had a very scientific approach, either in subject matter or execution of the work. Being able to combine both art and science when creating skincare formulas is endlessly fascinating, and I consider myself extremely fortunate that I have discovered this form of art.

That being said, it’s time for a science lesson.

When our skin feels dry, tight, and uncomfortable, we apply a moisturizer – but how do moisturizers actually work to make our skin feel better?

epidermis

Diagram of the layers found in the epidermis.

It starts with understanding the layers of our skin. Most of us know that the epidermis, dermis, and subcutaneous layer makes up the skin. Within the epidermis, however, there are even more layers, and these are what we are treating when we apply moisturizers.

Under normal circumstances the topmost epidermal layer, the stratum corneum (SC), is the main barrier to protect skin from moisture loss and environmental stressors. The SC has natural moisturizing factors (NMF) to prevent against transepidermal water loss (TEWL). NMF properties keep the SC flexible, which prevents cracking and flaking.

Still with me?

Dry skin conditions appear when the barrier function and NMF have been compromised. When the stratum corneum moisture content drops below 10%, it is perceived as dry. The ways this can happen are too many to list for this post, but the end result is skin that is flaky, tight, uncomfortable, and in extreme cases it can crack and bleed.

So, we reach for a bottle of lotion. A well-formulated one provides immediate skin benefits and also helps stimulate the production of natural barrier-building substances such as epidermal lipids and NMF. Most formulas work with three basic types of moisturizers; occlusives, emollients, and humectants.

Occlusives

This class of ingredients creates a barrier over the skin, trapping water in the epidermis and stopping evaporation. Occlusives are hydrophobic, meaning they repel water, and the trick when formulating with them is to find a balance that blocks the passage of water out of the skin without completely occluding the pores. Depending on where the product is to be used, you may want to avoid some heavier occlusives; for instance, you wouldn’t want something as heavy as beeswax or castor oil to be used on the face because they can be comedogenic (blocking the pores and causing comedones, like whiteheads or blackheads).

Common occlusives used in Bonnie products are plant oils like almond, marula, and argan oil, and waxes such as carnauba, candelilla, and beeswax.

Emollients

The word emollient is derived from the Latin word mollia, which means soft. Emollients are ingredients that traditionally impart a smooth, lubricious feeling on the skin. However most emollients used today are multi-functional and have numerous benefits, such as thickening the formula, improving skin elasticity, reducing the appearance of wrinkles, and increasing cell turnover.

There are several chemical types of emollients, including esters, fatty alcohols, fatty acids, ethers, silicones, and hydrocarbons.

Some of the naturally-derived emollients used in Bonnie skincare products include olive squalane (hydrocarbon group), caprylic/capric triglyceride (ester), stearic acid (fatty acid), cetyl alcohol (fatty alcohol), bamboo isoflavones (silicone), and meadowfoam seed oil (fatty acid).

Humectants

Humectants are hydrophillic ingredients that attract water (the opposite of an occlusive). Used in skincare, they can do two things; draw water from the atmosphere into your skin, or draw water from the lower skin layers up into the epidermis. In formulation, humectants are used with occlusives to draw water into the epidermis and keep it there. Humectants also promote the production of ceramides, which are crucial components of NMF.

Naturally-derived humectants used in Bonnie products include glycerin, 1,3-propanediol, honey, and sodium lactate.

____

There are many other types of ingredients which can contribute to a successful moisturizer, but basic no-frills lotions should have ingredients from each of the occlusive, emollient, and humectant categories.

 


Sources:

Epidermis image https://mutagenetix.utsouthwestern.edu/phenotypic/phenotypic_rec.cfm?pk=359

Molecular basis for stratum corneum maturation and moisturization http://onlinelibrary.wiley.com/doi/10.1111/bjd.13303/full

Everyone should know the difference between the three types of moisturizers http://www.businessinsider.com/how-do-moisturizers-work-to-keep-your-skin-soft-and-smooth-2015-7

Stratum Corneum Moisturization at the Molecular Level http://www.sciencedirect.com/science/article/pii/S0022202X94904472?_rdoc=1&_fmt=high&_origin=gateway&_docanchor=&md5=b8429449ccfc9c30159a5f9aeaa92ffb&ccp=y

Stratum Corneum Moisturization at the Molecular Level: An Update in Relation to the Dry Skin Cycle http://www.jidonline.org/article/S0022-202X(15)32301-0/fulltext

An Overview of Emollient Technology http://knowledge.ulprospector.com/5840/pcc-emollient-technology-overview/

Moisturizing Strategy: Tips and Recommendations for Formulation http://knowledge.ulprospector.com/883/pcc-moisturizing-strategy/

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