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Skin Care Moisturizers
By: Eric S. Abrutyn, TPC2 Advisors Ltd., Inc.
Posted: November 30, 2010, from the December 2010 issue of Cosmetics & Toiletries.
Moisturizers are an important category of personal care products,1 and such formulas are designed to add moisture to the skin. Developing a good moisturizer requires carefully balancing the ingredients in a formula so that, upon application, the product maintains proper water content in the skin, i.e., 10–30%, to maintain its plasticity and barrier integrity. Insufficient water content can lead to the thickening or thinning of skin; fissure development, which produces chapped, rough and cracked skin; and the loss of pleasing skin aesthetics. Therefore, choosing the right moisturizer requires knowledge of its chemical, physical and performance properties and how to best utilize it against the targeted performance claims and consumer expectations. In addition, it requires knowledge of the skin to which it will be applied.
In general, skin conditioning needs can be classified based on skin health: normal, varying degrees of dry, oily, sensitive, dermatologically damaged and mature. There are other ways to classify skin types, most notably by the well-known and modified Fitzpatrick systems, all of which are more centered on the physiological health of skin and effects of sun exposure. Skin discomfort is unacceptable to consumers, thus moisturizers containing emollients and humectants are used to help alleviate the symptoms of skin discomfort. Since moisturizing lotions provide temporary relief of these symptoms, they are applied to the skin as a constant routine for skin management, to help to provide a healthy skin feeling. Following is an abbreviated explanation of the performance criteria of moisturizers, humectants and emollients.
Approaches to Moisture
Moisturizers: Moisturizer is a generic term used to signify an ingredient that adds moisture to the skin; to refer to humectants, which maintain skin hydration; and to describe emollients that soften skin.2–4 Unfortunately, these terms are used interchangeably but each of these materials provides different performance benefits to skin and is quantified by different clinical methods. Moisturizer typically describes the function of a finished product and tends to include polar materials that are hygroscopic and able to hold water in place. The skin’s natural moisturizing factor (NMF) also plays an important role in moisturizing the stratum corneum (SC).5 The average NMF composition consists of approximately: 40% amino acid; 12% PCA; 12% lactate salt; 7% urea; 1.5% glucosamine/creatinine; 0.5% citrate salts; 18.5% Na, K, Ca or Mg phosphate; chlorine; and 8.5% sugars, organic acids and peptides. Thus, moisturizing ingredients are chosen based on their ability to substitute, replenish or maintain skin’s natural moisturizing components.
Classic moisturizers: Classic ingredients used as moisturizers include petrolatum as an occlusive barrier to hold moisture in the epidermis and SC; dimethicone (250–5000 cps) to modulate moisture in the skin; lanolin and its derivatives; vegetable butters/oils and their derivatives, e.g. shea butter, avocado oil, olive oil, etc.; high molecular weight linear fatty acid esters such as arachidyl propionate and cetyl palmitate; potassium lactate, alkyl methyl siloxanes, e.g. C30-45 alkyl dimethicone; and film-forming polymers.
Humectants: Humectants are ingredients that have hygroscopic properties and can thus modulate moisture and retard moisture loss from skin.3, 6 They typically are associated with skin moisturization and can be divided into two classes of chemistry—inorganic, e.g. calcium chloride, etc., and organic, including polyols, organic salts and amino acids. Popular humectants include glycerin, urea, pyrrolidone carboxylic acid (PCA) and others (see Commonly Used Humectants). They provide good water-binding capacity with good skin substantivity.