FORMULATING FOR MILDNESS 75
The safety of using soap on the face was first raised as an issue before WW2, but it was not until 1948 that wash bars based on nonalkaline synthetic surfactants were introduced in the US. However, the safety of these was soon called into question and there followed much testing to explain why skin dryness was reported after exposure to alkyl sulfate-containing products. To this day, no one theory has provided an unequivocal answer, although an increase in transepidermal water loss (TEWL) generally followed alkyl sulfate exposure.2 Today most of the ‘soaps’ available are in fact syndet bars, which differ from traditional soap bars in formulation and chemistry. Produced from blends of synthetic surfactants derived from oils, fats, or petroleum, they are made using a variety of chemical processes other than traditional saponification. These synthetic surfactants can produce mild products which are often pH neutral and marketed as ‘cleansing bars’ or ‘dermatological bars’. Often the term ‘soap free’ is applied, which can cause confusion although it is technically correct. The first soap bar was Dove - launched in 1955.3
Choosing a safe surfactant system is vital
for formulators creating effective and safe products. In vivo and in vitro data should be consulted before a selection is made, but end testing is essential. Negatively charged anionics are the usual basis for any wash product. They provide the best detergency and also excellent foaming/lathering qualities. They are also the group most likely to be irritating to skin, so are used in combination with other surfactants which lower irritancy. Non-ionics have detergency which is usually equal and sometimes superior to anionics, but due to their poor foaming characteristics they are seldom used as a primary surfactant. They are often very useful co-surfactants.
The material polysorbate-20, used in conjunction with anionic and amphoteric surfactants, reduces eye irritation. It is also a very useful solubilser of perfumes and essential oils. Alkyl polyglucosides (APGs) are a group of non-ionic surfactants based on sugar which are fully biodegradable and widely used in organic certified formulations.
Amphoterics are negatively or positively
charged depending upon the pH level. When a low pH is avoided they are almost completely non-stinging to the eyes and they are widely compatible with other surfactants. Cocamidopropyl betaine is a popular co-surfactant as it adds mildness and viscosity to formulations. Positively charged cationics do not have good detergency or foaming properties, but they are great conditioners. Therefore, they are widely used in conditioners and at
April 2018
lower levels in conditioning shampoos and body washes, although not all are stable in anionic surfactant systems so careful selection is necessary. Their inclusion does impact on foam levels, so they are used in wash products at quite low levels. Certain blends of surfactants have been
produced by raw material manufacturers with specialist characteristics. For example, the Rita series of acyl lactylates are anionics which result from the reaction of fatty acid with lactic acid, and are neutralised with a cation to create a very mild non-stripping, non-irritating surfactant. They are substantive to the skin and hair, binding to proteins found on the surface, and provide a silky, soft feel that helps hold moisture at significant levels. Pationic ISL (Sodium Isostearoyl Lactylate) in particular has a strong capacity to hold water into the skin.
Non-drying
Moisturisation and preventing water loss are important for mild products because anything that dries the skin and leaves it uncomfortable is justly deemed as harsh. Dry skin is uncomfortable. If moisture levels in the skin aren’t maintained then skin can look creped or wrinkly, and if it becomes very dry it can flake. Dry skin exhibits enhanced transepidermal water loss (TEWL), which is the loss of water that passes from inside the body through the epidermis to the surrounding atmosphere via diffusion and evaporation processes. Good cosmetics should put moisture back into our skin, protect the skin barrier function and certainly not contribute to further damage. There are a number of raw material groups which can improve skin comfort. Humectants help prevent TEWL and are often moisturisers. By reducing the unattractive appearance of dryness, they
provide immediate and long-term improvement to the skin’s appearance. Glycerin is a popular, cost-effective humectant used in a variety of cosmetics to draw water to the skin and can be an especially useful addition to wash products. Panthenol is widely used in both skin and hair care formulations to improve hydration. Sodium hyaluronate has high hygroscopic capacity, even at low humidity, and certain grades can hold up to 1000 times their own weight in water. High molecular weight grades provide film-forming that reduce TEWL and low molecular weight grades can penetrate further into the skin. It is used in many skin care formulations to improve hydration and texture.
Poor skin barrier function leads to TEWL and eventually sensitised skin. To improve this function refatting agents can be applied; BASF’s Lamesoft®
range for
example is a collection of lipid layer enhancers which can be used in all wash care products. Lamesoft OD is a refatting agent with data on oil deposition demonstrating its value in all rinse-off products. The microemulsion of emollient, wax and alkyl polyglucoside has been shown to significantly improve skin-feel, softness and smoothness while reducing dryness. Lamesoft PO 65 is a blend of coco glucoside and glyceryl oleate, which is a component of human skin. The higher the level it is used at, the better its skin care benefits. At 1% it has proven lipid layer enhancing properties, at 3% it perceivably improves the softness and smoothness of skin and at 5% it provides 24-hour moisturisation for intensive care claims. It provides ultimate mildness for baby and facial wash products as well as being a natural thickener for ‘green’ cleansing concepts.
PERSONAL CARE EUROPE
©suriya/Fotolia
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