The primary purpose of cleansing is to remove oil, bacteria, sweat, dirt, and desquamated skin cells from the face and body. However, cleansers can react with lipids and proteins on the skin and incite keratinocytes to release cytokines, all of which can irritate or damage the skin’s surface.1,2 Surface-active substances, known as surfactants, work by reducing the surface tension on the skin and emulsifying dirt.3 There are various kinds of surfactants found in cleansers.
ANIONIC (NEGATIVELY CHARGED) SURFACTANTS
Anionic surfactants form generous foam and have the highest cleansing power. Consequently, these compounds are often found as the primary surfactants in cleansers (Table 6-1). “Soap” contains the anionic surfactant alkyl carboxylate. These anionic agents are potent irritants to the skin,4 and have been found to cause harmful swelling of cell membranes.5,6 The well-known anionic agent (a type of alkyl sulfate) sodium lauryl sulfate (SLS), which strips lipids from the skin, is so irritating that it is used in the research setting to impair the skin barrier in order to test “barrier repair products.” Sodium laureth sulfate (or sodium lauryl ether sulfate, also known as SLES) has good cleansing power but is less likely to provoke irritation than SLS.
TABLE 6-1Anionic Agents used in Surfactants ||Download (.pdf) TABLE 6-1 Anionic Agents used in Surfactants
Alkyl acyl isethionates
Alkyl ether sulfates
Alkyl ethoxy sulfates
CATIONIC (POSITIVELY CHARGED) SURFACTANTS
Cationic surfactants have lower detergent properties than anionic surfactants and are very irritating, but are typically used because of their antimicrobial properties. These surfactants often lead to the hand dermatitis seen in frequent hand washers. Cetrimide, chlorhexidine, and benzalkonium chloride are examples of cationic surfactants.
Amphoteric surfactants exhibit changing properties depending on the pH of the solution. Amphoterics are popular because they lather well, exhibit good cleansing power and compatibility with different pHs, display moderate antimicrobial activity, and cause minimal irritation. Examples include cocamidopropyl betaine, cocoamphoacetate, and cocoamphodiacetate.
Nonionic agents have no electric charge. They are expensive and demonstrate poor cleansing characteristics but are believed to cause less irritation than anionic or cationic cleansers. Nonionic agents have been found to disrupt the skin barrier by solubilizing fatty acids and cholesterol.2 Examples of nonionic surfactants include cocoglucoside, lauryl glucoside, decylglucoside, and coconut diethanolamine (cocamide DEA).
Several factors influence the irritancy potential of cleansers including the amount of time left on the skin, rinsability, pH, and the susceptibility of the skin to irritation. (Individuals with a Baumann Skin Type designated as S4 are more susceptible to irritation because their skin barrier is impaired.) The surfactant type is the main influence on irritancy. Surfactants with C10–C14 chain lengths are the most aggressive because they are the most active in solution.
NEWER CLASSES OF CLEANSERS
Attempts to diminish the irritancy of soaps through the addition of secondary components have led to the development of newer classes of cleansers such as superfatted soaps, transparent soaps, and combination bars (combars). Bars composed of synthetic surfactants are often referred to as “syndet bars.” These surfactants have a neutral pH, and include ingredients such as alkyl glyceryl ether sulfonate, α-olefin sulfonates, betaines, sulfosuccinates, sodium cocoyl monoglyceride sulfate, and sodium cocoyl isethionate. Organic preparations are also available and include ingredients such as saponins and sucrose laurate.
NATURAL INGREDIENTS IN CLEANSERS
Saponins are a large family of structurally-related compounds derived from plants. The word “saponin” originates from the plant genus Saponaria. Many saponins manifest foaming characteristics that make them a good option for natural or organic cleansers. Saponins are composed of a steroid or triterpenoid aglycone (sapogenin) linked to one or more oligosaccharide moieties by glycosidic linkage.7 The foaming action of saponins emerge by dint of the combination of the nonpolar sapogenin and the water-soluble side chain. The Sapindus mukorossi (soapnut) plant has been used as a natural cleanser and displayed antimicrobial activity in one study.8–11 Camellia oleifera has been shown to exhibit notable detergent abilities.7 Several plants contain saponins, including alfalfa foliage, peas, chickpeas, horse chestnut trees, soybeans, and daisies. Desert plants, including Yucca schidigera and Quillaja saponaria, are good sources of saponins and are found in natural cleansers on the market.
The choice of cleanser is pivotal for individuals that suffer from excessively oily or dry skin. Oily skin benefits from foaming cleansers that can strip unwanted sebum lipids from the skin, while people with dry skin are better served with lipid-sparing gentle cleansers such as milks and creams.
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