Keith Ertel1,2, Heather Focht1, and Karl Wei1 1 Procter & Gamble Co, Cincinnati, OH, USA 2 KDE Scientific Consulting, LLC, Sheboygan, WI, USA Cleansing to remove soils from the skin’s surface is a basic human need that serves both a cosmetic and health function. While facial cleansing receives considerable attention and the need for specialized facial cleansers is generally recognized, cleansing needs for the body are often given little thought, the assumption being that any personal cleanser will suffice. This view is somewhat surprising given that body skin accounts for more than 90% of the body’s total surface area and, as we will show, consumers have diverse needs and expectations from a body cleanser. Water alone cannot effectively remove all soils from the skin surface and surfactant‐based materials have been used as cleansing aids throughout recorded history. Surfactants, or surface‐active agents, possess both hydrophilic and lipophilic character and it is this dual nature that allows surfactants to enhance removal of oily soils from the skin surface. Soap is a surfactant and was among the first cleansing aids used. Some of the earliest references to soap preparation are found in Sumerian and Egyptian writings, although legend holds that the article we now know as soap originated by chance at Mount Sapo in Ancient Rome, when fat and wood ash from animal sacrifices were mixed by rainwater and reacted. Regardless of its origin, soap was the cleansing aid of choice for many centuries. Soap is an effective skin cleanser but has some drawbacks, for example reduced solubility in hard water. And soap can dry the skin. An important change in personal cleanser technology occurred around the time of World War I when the first nonsoap or synthetic detergent (syndet) cleanser was introduced. Synthetic detergents offer increased hard water solubility, and some have improved skin compatibility compared to soap. Cleansing bars, whether soap‐ or syndet‐based, remained the predominant product form for body cleansing until the latter part of the twentieth century, when liquid personal cleansing products for the body, such as body washes, were introduced and began to gain a foothold. These liquid cleansers are now commonplace in many markets and their use continues to increase. Shower gels are similar to body washes, but many sources distinguish these liquid cleansers from body washes on the basis of their thicker consistency. Body washes offer a number of advantages over bar cleansers. The formulas are often syndet‐based and as such can provide enhanced skin compatibility compared to soap‐based cleansing bars. Body washes are also less messy in‐use than bars (e.g. no mush), are more hygienic, and offer a greater potential to deliver materials intended to benefit skin. Many body washes contain ingredients to moisturize and improve dry skin or to provide other benefits. For example, some work shows that body washes can help mitigate photodamage via deposition of antioxidants or sunscreen ingredients on the skin [1–3]. On the downside, body washes can be less convenient to transport and can be more expensive on a per‐use basis than commodity cleansing bars. And while body wash formulas may contain ingredients intended to benefit skin, formulating a product that will deposit an effective amount of said ingredients on the skin during rinse‐off use can present a considerable challenge. Body wash products available in the market fall largely into one of three categories. Regular body washes are products whose primary function is to provide skin cleansing. As such, these products are usually based on a relatively simple chassis. Fragrance often plays an important role in such products to define product character, to influence purchase, or to evoke a physiological or psychological response in‐use or on the skin [4, 5]. For example, the calming effect of lavender is widely reported and a cursory search of the internet shows that this is a popular scent for body wash products. Moisturizing body washes are intended to not only cleanse skin but also provide dry skin improvement. However, there are different ways to define such improvement. In some cases, a product is formulated with “mild” surfactants and its ability to improve dry skin is judged relative to another (drying) personal cleanser. In this situation, the improvement in dry skin is a result of producing relatively less dryness than the benchmark product. This is sometimes termed passive moisturization. In other cases, a product contains one or more moisturizing ingredients that deposit on skin during use, and its effect on dry skin is judged relative to an untreated or water‐only control. Dry skin improvement thus reflects the effect of the product relative to the condition of unwashed skin. This is sometimes termed active moisturization. Thus, moisturizing body washes can provide markedly different levels of dry skin improvement depending on the criterion used to judge their performance. Finally, there are products that fall into a category best described as specialty body washes. These are extensions of regular and moisturizing body washes that contain ingredients intended to provide additional function or benefit. Examples include products that contain beads or other grit material (e.g. pulverized fruit seeds) to provide exfoliation and an enhanced dry skin benefit, and products that contain menthol or other sensates to provide a “cooling” or “tingling” sensation to the skin. And as already noted, some body washes might be used to deliver benefit agents other than moisturizers to the skin, e.g. sunscreen or antioxidant materials. Unlike their cleansing bar counterparts, body wash formulas contain a high percentage of water. This presents a double‐edged sword. On the one hand, eliminating the need to form materials into a bar that will hold its shape while maintaining good performance and wear characteristics removes a number of formulation constraints, and this greater freedom introduces the possibility of incorporating relatively high levels of noncleanser materials, such as ingredients to provide skin benefits, into the formulation. On the other hand, the aqueous milieu present in body washes and other liquid cleansers introduces issues not present in bars. For example, physical stability is a consideration. Many benefit agents are lipophilic in nature and an improperly formulated liquid cleaner may exhibit phase separation or creaming, not unlike the separation of oil and water phases that occurs in some salad dressings. Chemical stability is also a consideration; the greater mobility afforded by an aqueous environment increases the likelihood of molecular interactions, and water itself can participate in decomposition reactions (e.g. hydrolysis). An aqueous environment also increases the potential for microbial contamination. Thus, formulating a body wash presents a number of challenges compared to bars. And as already noted, there is the additional consideration of assuring the formula will deposit an efficacious amount of benefit ingredient(s) on the skin if a product is intended to provide an effect beyond basic cleansing. Surfactants are the workhorse ingredient in any personal cleansing product. Water is capable of removing some soils from the skin; however, sebum and many of the soils acquired on the skin through incidental contact or purposeful application (e.g. topical medicaments) are lipophilic in nature and are not effectively removed from the skin’s surface by water alone. Surfactants, or surface‐active agents, have a dual nature; part of a surfactant molecule’s structure is lipophilic and part of it is hydrophilic. This structural duality allows surfactant molecules to localize at the interface between water and a lipophilic soil and lower the interfacial tension to help remove the soil. Further, surfactants allow water to wet the skin’s surface more effectively and help to solubilize lipophilic soils after removal, which prevents the soils from redepositing on the skin during rinsing. Surfactants are also responsible for the formation of bubbles and lather, which most consumers view as necessary for effective cleansing. As with cleansing bars, the surfactants available for use in liquid personal cleansers and body washes fall into two primary groups: soaps and nonsoaps, i.e. syndets. Soap is chemically the alkali salt of a fatty acid formed by reacting fatty acid with a strong base, a process known as saponification. The fatty acids used in soap manufacture are derived from animal (e.g. tallow) or plant (e.g. palm kernel oil) sources. These sources differ in their distribution of fatty acid chain lengths, which determines properties such as skin compatibility and lather forming ability [6, 7]. Soap’s properties are also affected by external factors such as water hardness; soaps are generally more irritating and lather and rinse poorly in hard water [8]. Some specialty body washes contain soaps derived from “natural” fatty acid sources such as coconut or soybean oil; these products will behave similarly to products containing soaps derived from traditional fatty acid sources. Syndets were developed to overcome shortcomings associated with soaps, such as the influence of water hardness on their performance, and to expand the pool of available raw materials used in surfactant manufacture. Syndets vary widely in terms of their chemical structure, physicochemical properties, and performance characteristics, including skin compatibility. Syndets are not necessarily less irritating than soaps. Sodium lauryl sulfate is an example; this material and other alkyl sulfates are often used as model skin irritants [9]. Many body washes are based on syndet surfactant systems, and because syndets have a wide range of performance characteristics, such formulas often combine several surfactant types to achieve specific performance characteristics in the finished product. For example, alkyl sulfates, while having relatively poor skin compatibility, lather well. Combining an alkyl sulfate with an amphoteric surfactant such as cocamidopropyl betaine, which exhibits good skin compatibility, can yield a formula with acceptable lather and skin compatibility. The addition of certain macromolecules to body washes can also improve skin compatibility and in‐use characteristics [10, 11]. Thus, formulating a body wash chassis with syndets often involves choosing surfactants and other ingredients to optimize performance, aesthetics, and skin compatibility. Some body washes contain ingredients that are intended to provide skin effects beyond simple cleansing. Dry skin, which is a pervasive dermatologic issue, is one of the most common benefit targets for body washes. Not surprisingly, moisturizing ingredients such as petrolatum, various oils, shea butter, and even glycerin, which are found in leave‐on moisturizers, are often used in moisturizing body washes. However, simply including a moisturizing ingredient in a rinse‐off product is not sufficient; the product must deposit an efficacious amount of the material onto the skin during the washing and rinsing process. And as previously noted, criteria for judging moisturizing efficacy differ. Our work shows that moisturizing body washes exhibit a wide range of effects on dry skin and that some can actually worsen skin dryness and irritation [12]. In addition to moisturizing ingredients to improve dry skin, body washes might also contain particulates such as beads or pulverized fruit seeds to aid exfoliation. A particulate’s size, surface morphology (i.e. smooth or rough), and in‐use concentration will determine its ability to provide such a benefit. Finally, body washes may contain ingredients such as antioxidants and sunscreens, which are intended to protect from or to reduce the effects of environmental insults. As with moisturizing ingredients, an efficacious amount of these materials must remain on skin after washing and rinsing for the product to be effective for this purpose. Body wash formulas contain additional ingredients that act as formulation and stability aids. The addition of polymers and salt will alter a product’s viscosity, which can modify performance characteristics and improve physical stability. Feel modifiers such as silicones are sometimes used to improve the in‐use tactile properties of body washes that deposit lipophilic benefit agents on skin. Chelating agents such as ethylenediaminetetraacetic acid (EDTA) and antioxidants such as butylated hydroxytoluene (BHT) and are added to improve chemical stability, and buffering a body wash formula to a specific pH value can help inhibit microbial growth and improve the product’s chemical and physical stability. Color and fragrance are an important part of the in‐use experience for many body washes. Colorants are usually present in relatively low amounts. Still, colorants used in cosmetics in the EU require safety approval before product marketing, and in the United States, cosmetic colorants require approval under the US Food, Drug, and Cosmetic Act. Fragrances are also usually present in relatively low amounts, although the apparent concentration may seem higher because of “bloom” that results from lathering a body wash on a mesh cleansing puff, the recommended application procedure for many of these products. Although exposure is reduced in rinse‐off versus leave‐on application, certain fragrances can be a source of cosmetic allergy in some individuals. Some body washes incorporate natural oils to impart fragrance but such occult fragrances are not without issue because some of these natural materials also have a potential cause sensitization. The mechanical action associated with applying a personal cleanser to the body helps to loosen and remove some soils, but surfactants are the primary agents responsible for aiding soil removal, particularly lipophilic soils. However, surfactants and the cleansing products based on them differ in their abilities to remove sebum and lipophilic soils [13]. These cleansing performance differences are a greater consideration in body washes than in bars because of the relatively lower surfactant concentrations present in the former compared with the latter. Because lipophilic soils present the greatest cleansing challenge, oil‐based makeup materials are often used as model soils in tests intended to measure cleansing efficiency. These materials are poorly removed from the skin by water alone and their inherent color makes them easy to detect and measure on the skin’s surface. To assess the cleaning efficiency of different skin cleansing products, we conducted a study that compared the cleansing abilities of a high petrolatum‐depositing body wash (HPDBW), a syndet detergent bar, and water [14]. A commercial oil‐based makeup product served as a model soil and was applied to discrete treatment sites on the volar forearms of 13 light‐skinned females. The makeup was allowed to dry for 15 minutes and baseline colorimeter L* values were recorded at each site. Lather was generated from each cleansing product in a controlled manner and applied to a randomly assigned site for 10 seconds with gloved fingers. The sites were rinsed with warm water for 15 seconds and allowed to air dry for 30 minutes then colorimeter measurements were repeated. The results, which are summarized in Figure 13.1
CHAPTER 13
Personal Cleansers: Body Washes
Background
Types of body wash products
Major formula components of body washes
Water
Surfactants
Skin benefit agents
Ancillary ingredients
In‐use performance considerations for body washes
Cleansing ability
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