Shampoo bars made of “all natural” ingredients are all the rage in the hair and skin care markets. These handmade soaps and shampoo bars are especially gaining popularity in the curly-hair community because they tend to be free of sulfates and silicones and are made from moisturizing oils and gentle cleansers. Many people report that they are extremely pleased with the results they are getting, citing benefits such as increased softness, better curl formation and, in some cases, elimination of the need to use conditioner. However, not all users have had such pleasant experiences, and there is some confusion over what the advantage is of shampoo bars over traditional shampoos or low- or no-poo cleansers. There is also some debate about whether the shampoo bars should be followed up with a vinegar rinse, a conditioner, or both. As I usually do, I will delve into the basic chemistry of shampoo bars to discover what answers lie beneath the surface.
What is a Shampoo Bar?
Soap molecules used in shampoo bars are similar to some of the more familiar hair cleansers such as sodium lauryl sulfate in that they are anionic (negatively charged) surfactants. The difference is that the polar head group of the molecule is a carboxylate, rather than a sulfate (R-COO-Na+ vs. R-OSO3-Na+), which results in a milder surfactant. They are formed by reacting a fat (triglyceride) with a strong base, either sodium hydroxide (lye) or potassium hydroxide (potash), in a process called saponification. In this reaction, the fatty acids are cleaved from the triglyceride backbone and in a two-step chemical reaction soap molecules are formed, along with water and glycerin. The amount of strong base needed is calculated based upon published saponification values for the fats being used in the process. Although the source of fats is natural, there is still a chemical reaction and modification that must be done to get a useful derivative.
Typically, an excess of oils is added to the mixture prior to the mixing of fats and base. This provides two benefits:
1. The lye is completely consumed in the chemical reaction, which makes certain the final product doesn’t burn or irritate skin or damage hair.
2. The excess oils act as “superfatting” agents in the shampoo bar, which contribute to mildness and an overall luxurious feel to the soap. These oils act as moisturizing and conditioning agents, much as they would in a regular shampoo or conditioner.
Most handmade soap makers use a “cold process,” where the main source of heat used is from the exothermic reaction itself (unless the oils or fats need to be pre-melted). The lye or potash is added slowly to water, which quickly becomes hot. It is set aside for a few minutes to cool slightly while the oils are mixed separately. The basic solution is then mixed with oils and stirred until it begins to thicken. Essential oils and colorants can be added at this time, and then the soap is poured into molds. After it cools for a few hours, it can be removed carefully from the molds and cut into bars if needed. These individual shampoo bars are then covered and left to “cure” on racks for a few weeks. This ensures that all of the lye is gone and that the soap is hard.
You may note that in this process, glycerin, a byproduct of the saponification reaction, is left to add humectant and lubricative properties to the soap. It is important to be aware of this because it can potentially be problematic for those with colored hair, especially if the hair was colored recently, if temporary dye was used or the if hair color was heavy in red dye. The humectant properties of glycerin can be a boon or curse for curly hair also, depending upon the hair type, condition of the hair, and environment in which the product user lives.
