Hair-Care Products

SHAMPOOS

•Shampoo is a hair care product used for the removal of oils, dirt, skin particles, dandruff, environmental pollutants and

other contaminant particles that gradually build up in hair. The goal is to remove the

unwanted build-up without stripping out so much as to make hair unmanageable

SHAMPOOS Shampoos are more than just hair cleansers. If cleanliness were the only goal, any heavy-duty laundry detergent would do a super job. But shampoos must also help keep hair healthy, soft, and shiny. These additional requirements call for a specialized product.

•Your hair, being all keratin, has many of the same requirements as your skin. In particular, it needs sebum as an emollient to soften it and give it natural body and luster. Every hair follicle has its own sebaceous gland for this purpose (see Figure 4.3). But sebum needs to be present in the optimum amount. With too little sebum, your hair is dry and strawlike; with too much, it is greasy and matted. Therefore, shampoos must be able to wash away the greasiness without removing the shine. They do this with mild surfactants (Section 3.1) that have only limited cleaning ability. Sodium lauryl sulfate (Figure 4.12) is the most widely used surfactant in shampoos. It helps you keep that "Goldilocks" quantity of sebum on your hair: not too much, not too little, but just right

Figure 4.3 Cross section of skin.

Harsh shampoo can damage hair. Extremes in acidity or alkalinity can cause your hair's protein to denature and decompose. Hair needs a pH between 4 and 6—that is, slightly on the acid side of neutral—to achieve its maximum wet strength. Because most surfactant-water mixtures are strongly alkaline, typically with pH values of 10 or more, shampoos often contain acids to lower the pH. The most common are citric acid (the same compound that gives tartness to citrus fruits) and phosphoric acid, a mild acid often found in soft drinks (Figure 4.13). So many people are uneducated in chemistry that manufacturers advertise their products as "nonalkaline" or "pH-controlled" or even "acid-balanced,"

but they don't dare say that their shampoos are acidic.

•The price of shampoo is higher than it needs to be because of those uneducated consumers. Each shampoo is filled with unnecessary ingredients including foaming agents (such as lauramide diethylamine; Figure 4.14) to make rich lathers, moderators to help the foaming agents work, and thickeners (such as lauramide diethylamine and sodium chloride) to give the runny liquids a richer texture. But the performance of the shampoo is not raised by any of these additives—only the price

Liquid Shampoo

•R/

•Texapon 15

•Water 85

Shampoo paste

•R/

•SLS 40

•Cetyl Alcohol 5

•Citric Acid 1

•Water 54