The skin is the largest organ of the human body with several important functions to perform. The skin protects us from the sometimes-harsh external environment (e.g. microbial invasion and physical injuries), regulates our body temperature, provides sensory input and eliminates waste. The skin can lose its ability to perform these functions when compromised or damaged.
While there are many causes leading to damaged or compromised skin, one main preventable cause is dry skin. The top layer of the skin, the epidermis, has an outer-most layer, the stratum corneum. The stratum corneum is where moisture content is controlled. Within the stratum corneum, two main components aid in this function–keratin and phospholipids. When the skin is healthy, these two components work in conjunction to keep out irritants and keep in moisture.
Dry skin occurs when the skin loses its phospholipid bilayers. The result is potential irritants entering and moisture exiting through the skin.
Thus, moisturizers can be used preventatively or to help restore the stratum corneum to its more normal function.
There are two means in which to moisturize the skin. Moisture can be added back into the skin or transepidermal water loss (TEWL) can be blocked or inhibited. TEWL is the process by which moisture migrates from the dermal tissues to the epidermis into the stratum corneum and evaporates into the atmosphere.
Moisturizers fall into two categories: lipids and humectants. Humectants attract moisture, and depending on their size (molecular weight), they are either absorbed into the skin or stay on the surface of the skin. Examples of humectants are glycerin, urea, and hyaluronic acid. Lipids perform differently than humectants by blocking moisture from leaving the skin. They are occlusive or semi-occlusive materials that are applied topically, provide a barrier and allow skin to better restore itself. Common lipids are petrolatum, lanolin, and mineral oil. Synthetic lipid materials are emerging technologies, which allow the lipid to penetrate the skin and fill spaces where natural phospholipids are missing. Lipids work best when applied soon after soaking, bathing, or showering. At this time, your skin will retain some of the moisture, and a lipid-based moisturizer will provide a barrier to moisture loss. The Skin Protectant Tentative Final Monograph for OTC drugs lists multiple materials with specific active percentages that protect injured or exposed skin or mucous membrane surface from harmful or annoying stimuli. These products can be used to lessen or inhibit TEWL. Some of the active ingredients are petrolatum, zinc oxide, dimethicone, allantoin, and glycerin.
Our skin performs many important functions–moisturizing the skin is an important step in maintaining healthy skin.