Anatomy of a Skin Cleanser

Cleansing Ingredients and Their Function

Cleansers are designed to remove oily soils, dirt, sweat, and sebum from skin through the action of surfactants.[1] Components of surfactants can bind to stratum corneum (SC) proteins, resulting in diminished ability of the SC to bind and hold water. Continued use of products formulated with harsh surfactants can dry skin and promote skin barrier damage, leading to erythema. Anionic surfactants ( Table 1 and Table 2 ) are often used in cleansers because of their excellent ability to foam and lather. Frequently, amphoteric surfactants ( Table 3 ) are used in combination with anionic surfactants in liquid cleansers because formulators consider amphoteric surfactants to be substantive to skin and act as skin conditioning agents while boosting foaming of the product. While synthetic surfactants are considered mild, impurities and changes in the synthesis of the material can alter irritation potential. Incorporation of nonionic, amphoteric, and cationic surfactants in a single formulation can further reduce the mildness of the anionic surfactant. Proteins, gums, and polymeric ingredients ( Table 4 ) may help reduce irritation potential.[2,4]

Surfactants are classified by their charge on the surface-active moiety:

  • Anionic (dissociation occurs in a negatively charged ion-anion)
  • Cationic (a positively charged ion is the carrier of the surface active properties)
  • Zwitterionic — commonly known as amphoterics (both positive and negative ions)
  • Nonionic (do not dissociate into ions in solution; commonly used in baby products; tend to suppress foam)

 

Cleanser Chemistry

Soap-based cleansers have dominated the industry. The manufacture of soap requires formation and neutralization of fatty acids from plant or animal triglycerides. The alkali alkanoates are further processed into pressed bars. While high-lathering soap is appealing to consumers, the irritation potential of soap is related to the alkalinity and fatty acid chain length (a palmitate is milder than a laurate) of the formulation.

Alkyl sulfates are considered to be highly irritating to skin. Chain length C-12- derived sulfates are believed to be responsible for the irritation. Water-soluble nonionic surfactants, betaines, and other surfactants may reduce irritation — possibly through reduction of free monomeric species in solution.

Sulfosuccinates, isethionates, tau-rates, and aliphatic and aromatic sulfonated hydrocarbons are in this group. Mildness appears to depend on the size of the hydrophilic head group and its accessibility to water. Some studies correlate skin permeation with the size of the hydrophilic head group on the sulfate. The isethionates are particularly mild and have a large hydrophilic head, as do sulfosuccinates and taurates. Aliphatic and cyclic sulfonates produce a less acceptable after-feel on skin and are less frequently used.

Anatomy of a Skin Cleanser

More recently available and apparently mild, these surfactants are more tolerant to low pH and also contain a large hydrophilic head group.

These surfactants contain both an acidic and a basic function in their structure. Their charge varies according to the pH of the system. At a lower pH, they are more likely to be irritating.[5] Formulators use amphoterics because they believe they are substantive to skin, acting as a skin conditioner. Two types used are alkylated amino acids and alkylamido alkylamines (sodium lauriminodipropionate).

These surfactants are frequently used in cleansers, producing foam in soft and hard waters. There is a possibility of sensitization in some betaines related to the presence of unquaternized amines.

The alkyl betaines are one of the few quaternary surfactants used in cleansing formulations, mostly in shampoos.

Nonionic surfactants generally are poor foaming agents. Many are used as solubilizers for lipids, helping to cleanse skin. Poloxamers, amine oxides and alkylglucosides are the key nonionic surfactants used in cleansing products.

Conclusions

A well formulated skin cleanser helps to maintain healthy skin. Hundreds of millions of people have used soap in the form of a bar or liquid with comparatively little irritation. Cleansers are designed to remove oily soils, dirt, sweat, and sebum from skin through the use of sur-factants.[1] Components of the surfactant may bind to SC proteins, reducing the ability of the SC to bind and hold water. Continued use of products formulated with harsh surfactants can dry skin, promote skin barrier damage, and eventually cause erythema.

Anatomy of a Skin Cleanser

Anionic surfactants are commonly used in cleansers because of their excellent ability to foam and lather. Frequently, amphoteric surfactants are used in combination with anionic surfactants in liquid cleansers to boost foaming of the product and because formulators consider amphoteric surfactants to be substantive to skin, acting as skin conditioning agents.[1]