Most cleansing is accomplished with a product known as soap, which is obtained through the chemical reaction between a fat and an alkali, resulting in a fatty acid salt with detergent properties. Modern refinements include adjustments in the alkaline pH to decrease skin irritation and to incorporate substances that prevent precipitation of calcium fatty acid salts in hard water, known as soap scum.
Nevertheless, modern soap is basically a blend of tallow and nut oil, or the fatty acids derived from these products, in a ratio of 4:1. Increasing this ratio results in superfatted soaps designed to leave an oily film on the skin.
Bar and liquid cleansers can be divided into 3 basic types, as follows: (1) true soaps composed of long chain fatty acid alkali salts with a pH of 9-10; (2) combars composed of alkaline soaps to which surface active agents have been added, also with a pH of 9-10; and (3) syndet, or synthetic detergent, bars composed of synthetic detergents and fillers that contain less than 10% soap and that have an adjusted pH of 5.5-7.
The purpose in developing new synthetic detergents is to provide a product that is less irritating to the skin than traditional soaps are. Common detergents in bar-type cleansers are sodium cocoate, sodium tallowate, sodium palm kernelate, sodium stearate, sodium palmitate, triethanolamine stearate, sodium cocoyl isethionate, sodium isethionate, sodium dodecyl benzene sulfonate, and sodium cocoglyceryl ether sulfonate.
Detergents in liquid formulations are sodium laureth sulfate, cocoamido propyl betaine, lauric acid diethenolamine (lauramide DEA), sodium cocoyl isethionate, and disodium laureth sulfosuccinate.
The normal pH of the skin is acidic, between 4.5 and 6.5. Applying alkali soap theoretically raises the pH of the skin, making it feel dry and uncomfortable. However, healthy skin rapidly regains surfactant; induced irritation remains a controversial area under investigation.
Special additives to the previously discussed formulations allow for the tremendous variety of soaps marketed today. Lanolin and paraffin may be added to a moisturizing syndet soap to create a superfatted soap, whereas sucrose and glycerin can be added to create a transparent bar. Adding olive oil instead of another form of fat distinguishes a Castile soap.
Medicated soaps may contain benzoyl peroxide, sulfur, or resorcinol antibacterials, such as triclocarban or triclosan. Triclocarban is excellent for eradicating gram-positive organisms, but triclosan eliminates both gram-positive and gram-negative bacteria. These soaps have a pH of 9-10 and may cause skin irritation.
Moisturizing syndet bar soaps contain sodium lauryl isethionate with a pH adjusted to 5-7 by using lactic or citric acid. These products are less irritating to the skin and are sometimes labeled beauty bars. Most bar soaps marketed by cosmetic companies are of this type.
Additives to soap also are responsible for its characteristic appearance, feel, and smell. Titanium dioxide is added in concentrations as high as 0.3% to opacify the bar and to increase its optical whiteness. Pigments, such as aluminum lakes, can color the bar without producing colored foam, which is considered an undesirable characteristic.
Foam builders, such as sodium carboxymethylcellulose and other cellulose derivatives, can make the lather feel creamy. Perfume in concentrations of 2% or more also can be added to ensure that the soap bar smells pleasant until it is completely used up.
Lipid-free cleansers are liquid products that clean without fats. They are applied to dry or moistened skin, rubbed to produce lather, and rinsed or wiped away. These products may contain water, glycerin, cetyl alcohol, stearyl alcohol, sodium laurel sulfate, and (occasionally) propylene glycol.
Lipid-free cleansers leave behind a thin, moisturizing film and can be used effectively to remove facial cosmetics and dirt in persons with sensitive or dermatitic skin. Lipid-free cleansers cause less cutaneous irritation in photoaged skin than other cleansers. However, propylene glycol can cause stinging, and sodium laurel sulfate is a detergent.
Cleansing creams are applied to the face both to clean and to moisturize. They are composed of water, mineral oil, petrolatum, and waxes. The classic cream for facial cleansing is known as cold cream.
Cold creams combine the effect of a lipid solvent, such as beeswax and mineral oil, with detergent action from borax, also known as decahydrate of sodium tetraborate. These products are popular to remove cosmetics and to provide cleansing for patients with dry skin.
Body washes are a special subset of liquid synthetic detergents that combine mild skin cleansing with moisturizing and emollient qualities. They are applied with a puff that does not support bacterial growth to break the emulsion through the incorporation of generous amounts of air and water. High amounts of petrolatum can be incorporated in body wash emulsions to improve skin dryness and hydration.
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