Here in this blog post, we will focus our attention primarily on shampoos as cleansing products for the hair and scalp. The word ‘shampoo’ is derived from Hindi word “Champo”, which means massaging or kneading. A shampoo is a liquid, gel, or a cream based upon surface-active materials that are capable of removing dirt or grime from the surface of the hair and scalp while producing foam during application and massaging of the hair and scalp. The early shampoos contained soaps that were prepared from neutralizing fats of oils with lyes such sodium or potassium hydroxides. These shampoos generally had alkaline pH in the range of 9.0 to 10.50. These liquid soaps were not very effective in cleansing the hair and scalp in the presence of hard water. Generally, hard water contains calcium and magnesium ions and they precipitate the soap, which is sodium or potassium salt of fatty acids such as stearic acid or coco-acid or oleic acid. These soap-based shampoos made hair alkaline and dull leaving behind a film of soap on the hair surface. If the hair is in alkaline pH range, generally, the cuticles are open and hair is weaker in its elasticity. Therefore, it is always desirable to not change the original pH of hair during the shampooing/cleansing process. From mid 20th century, a new class of cleansing agents was synthesized and they gained popularity over the soap – based cleansing products. These shampoos were high foaming; they performed very well in hard water and left hair surfaces squeaky clean and without a dull film on the surface of hair and scalp.
The detergents can be classified into mainly five classes such as anionic, cationic, amphoteric, non-ionic detergents, and natural or derived from naturals. The anionic detergents carry a negative charge; where as cationic detergents carry a positive charge. The amphoteric detergents carry both positive and negative charge. The non-ionic detergents do not carry any charge.
The major class of detergents that is employed in shampoos at appreciable amount is anionic in nature. The anionic shampoos are negative charged and produce rich and dense foam. The International Nomenclature of Cosmetic Ingredients (INCI) commonly used as anionic detergents are Sodium Lauryl Sulfate, Ammonium Lauryl Sulfate, TEA-Lauryl Sulfate, Sodium Laureth Sulfate, Ammonium Laureth Sulfate, TEA-Laureth Sulfate, and Sodium C14-16 Olefin Sulfonate. Some of these detergents are considered harsher to hair and scalp at their normal usage level of 15.0 %. These harsher detergents dry the hair and scalp to an appreciable level. The trans epidermal water loss (TEWL) of scalp is higher for Sodium Lauryl Sulfate and Ammonium Lauryl Sulfate, as compared to Sodium Laureth Sulfate and Ammonium Laureth Sulfate. Therefore, it is important to note that laureth sulfates are milder to scalp as compared to lauryl sulfates. Other anionic detergents are Alpha –Olefin Sulfonates such as sodium C14-16 Olefin Sulfonate and Disodium Lauryl Sulfosuccinate are also drying to scalp at 15.0% usage level. Lower concentrations are less drying to scalp but may not produce sufficient foam during shampooing. Again, the Disodium Laureth Sulfosuccinate is not as drying to scalp at 15.0% level. There is a large market trend towards using “Sulfate Free shampoos” in order to avoid the dryness of the hair and scalp, especially for those with African descent and curly hair types. There are five other sub-classes of anionic detergents and they are N- acyltaurides (Sodium Methyl Cocoyl Taurate), acylisethionates (Sodium Cocoyl Isethionate and Sodium Lauroyl Methyl Isethionate), polyethoxylated carboxylic acids (Trideceth-7 Carboxylic Acid), alkaline salts of N- acyl amino acids (Potassium Cocoyl Hydrolyzed Collagen), and sodium or potassium salts of fatty acids (Sodium Stearate or Potassium Stearate) also known as soaps. The taurates, isethionates, and alkaline salts of amino acids are gentler to hair and scalp as compare to lauryl sulfates. This sub-class of anionic detergents does not foam well and they are generally used as secondary detergents.
The amphoteric detergents are detergents that carry both a positive and a negative charge. They act as positively charged conditioners at low pH and cleansing detergents at alkaline pH. These detergents are considered gentler to hair and scalp. The most commonly used amphoteric detergents are Disodium Cocoamphodipropionate, and Sodium Cocoamphoacetate. This class of detergents does not foam well compared to anionic detergents such as sodium or ammonium lauryl sulfates but it is gentler to hair and scalp and the scalp does not lose more moisture. For a premium ethnic hair and scalp shampoo, normally a high level of amphoteric detergent such as Disodium Cocoamphodipropionate with a small amount of an anionic detergent such as Trideceth-7 Carboxylic Acid and or Disodium Laureth Sulfosuccinate are used to boost the foam. This type of combination of detergents is very mild to the hair and scalp and does not dry out the scalp.
The most commonly used detergents in this class are alkylglycosides and they are derived from natural sources. They are moderate in their foaming quality and are biodegradable. These detergents are becoming more popular nowadays because of the demand for natural or derived from natural materials. To name a few, the names that appear on the shampoo labels are Decyl Glucoside, Coco-Glucoside, and Lauryl Glucoside, etc.
These are amine oxides and quaternary ammonium chlorides such as Cetrimonium Chloride. They possess a positive charge and therefore, act as mild conditioning agents while producing moderate to poor foam. The amine oxides help to stabilize foam and help build viscosity of a shampoo. The names that may appear on the label in this class are Cocamine Oxide, Stearamine Oxide, Oleamine Oxide, Soyamidopropylamine Oxide, Tallowamine Oxide, Tallowamidopropylamine Oxide, Cetrimonium Chloride, Oleakonium chloride, etc.
Saponins: The Saponins are present in natural ingredients such as Soap Nuts (Areetha or Reetha available from Pakistan and India). Saponins are also present in Agave and green peas. The extracts based upon these natural sources are poor foamers and are not able to replace synthetic detergents. However, they can be combined with synthetic detergents in semi-natural shampoos.
In my next blog post we will talk in more detail about the history of shampoo and then give an overview on selecting the correct shampoo for different hair types.