How Simple soaps, Superfatted soaps, Shaving soaps and syndet bars differ?
Traditional and simple soaps are usually sodium salt of fatty acids, these fatty acids may be obtained from animal or plant sources. The pH of these soaps are typically in the range of 9 to 11 as they are salts of weak acids that form alkaline solutions on dissociation in water. Traditional soaps are not irritating to skin but modify the pH of skin that is around 5.5, for some time. The acidic pH is necessary for normal functioning of skin. The fatty acids used in soap making are generally of natural origin, derived from animal or plant sources, having anything between 12 to 18 Carbon chain. The most common coconut fatty acid has 12 carbon long chain, where as tallow/rendered animal fat has 18 carbon chain. Soaps made using 12 – 14 carbon fatty acids are soluble, lather easily and have good aesthetic properties. Whereas soaps made using 16 to 18 carbon fatty acids are easy to formulate into solid bars. Hence many formulators prefer a blend of different fatty acids to give soap the desired characteristics. The plant oils used in soap making are mostly triglycerides and when treated with lye and/or caustic soda they hydrolyze to the fatty acid sodium salts (soap) and glycerol.
Due to above mentioned factors simple soaps act, as good cleansers but tend to dry the skin. To overcome this limitation superfatted soaps were introduced in the market, these soaps are made in such a way that they leave some free fatty acid on use. Since they contain an excess of free fatty acid they are called superfatted soaps. This excess fatty acid reduces the lipid stripping and drying effects of a soap bar to a small extent. Beauty soaps available in the markets today are typically superfatted soaps.
The key difference between normal toilet soap and shaving soap is that shaving soaps are made by addition of caustic potash(KOH) to the saponification process; in combination with the correct choice of fatty acids, this creates a softer soap base with enhanced lathering characteristics. The control of free alkali is crucial and these soaps are often given a free fatty acid finish to minimize the risk of irritation in use. Processing is very similar to regular toilet soap and again the choice of a suitable superfatting material is essential to provide a good after-feel to the skin.
Technically syndet bars are Non - soap detergent bars, this technology has gained immense popularity across the globe. First time a syndet bar was introduced to the US market in 1957 as the Dove bar, the Dove bar is made using patented acyl isethionate as the surfactant component in combination with stearic acid which has a dual function of providing the physical characteristics for forming a stable bar and also acting as a significant skin protecting and moisturizing ingredient. The high level of stearic acid in the Dove bar is the basis of the one - quarter moisturizing cream in the product. When the patents for this novel technology ran out, several other acyl isethionate bars were introduced in the USA market including Caress, Olay, Cetaphil, and Aveeno. Because soap is cheap and easy to manufacture the cleansing bar market have remained predominantly soap bars but now is tilting towards syndet bars.