Colloid & Surface Phenomena
CE457/527
4/9/2002
Moisturizing Lotion
Jason Ashbery
Jonathan Danner
Haohao Huang
Leigh Vorreuter
I. Introduction
The general title cosmetics are applicable to a wide array of products. Some cosmetics such as blush or eye shadow are used to enhance the color of the person’s eyes or cheeks. Other cosmetics are used to protect the skin, for an example to delay the aging process. Some examples are lotion, creams, and sunscreen. Each one is different and carries different responsibilities.
Lotion can hold many different responsibilities. Lotion is considered a cosmetic product. It should improve the skin and have many useful purposes. Some lotions contain sunscreen that contains UV protecting agents that may reflect the harmful affects of the sun. Other lotions contain alpha hydroxides that improve the appearance of the skin. These beneficial attributes need help to deliver the wanted components to the skin and cause adhesion to the skin and also penetrate the skin.
There is a huge assortment of lotions to assist in customer’s needs. Some people prefer scented lotions compared to unscented. Others like quick absorbing lotion. Lotions sometimes need to be very sensitive to a person’s skin. A person may need lotion to heal dry skin while another might use it to prevent dry skin. Some women may feel like their skin has aged and some “age defining” lotion can help the skins appearance. There are many different varieties of lotions for instance; for dry skin, for extra dry skin, and for sensitive skin. Some contain sunscreen and others have desired fragrances.
They are many different manufacturers of moisturizing lotion. The manufacturers market their products towards age and gender. A young girl would be more likely to buy from Bath & Body Works because they have lotions that are scented and their labeling is colorful and attractive. Men on the other hand prefer non-scented lotions. Keri and Curel make non-scented lotions. Other manufacturers such as Bristol-Meyers Squibb lean more towards the pharmaceutical side of lotions.
The manufacturers have product specifications related to customer needs. These specifications are very important towards the characteristic of the lotion and are usually over looked by the customer. The lotions need to have an appropriate shelf life and it needs to have a good physical and chemical stability as well as cosmetic appeal. This is essential for any lotion because if the lotion has a short half-life the mixture will separate and not be able to be used. It also needs to reach its goal of moisturizing which means the active ingredients need to reach the desired target. The lotion has to be non-irritating to the skin and the pH needs to be a consideration. Lotions also must be fast absorbing and non-greasy. The duration that the lotion stays on the skin is important. It also needs to be long lasting. The lotion needs to go on smoothly and evenly and removed from the skin when it is appropriate.
The product design considerations are an essential part of the manufacturing process and the formulation of the moisturizing lotion. A manufacturer must identify their consumers needs are establish the appropriate product specifications in order to be successful.
II.Components and Composition
There are many different brands of moisturizing lotion on the market today. Most manufacturers also make several different formulations of the same brand. The result is a relatively large number of formulations for the consumer to choose from. It is important to realize however, that most of the lotions being sold share several of the same components. Two major differences between competing brands are noted in this section.
Component listings may vary significantly from product to product based on the color and scent of the lotion. These various fragrances and dyes may seem to monopolize the ingredient list, but they are only present in extremely small percentages.
The second difference is definitely not as obvious as the first. Lotion manufacturers use various surfactants to enhance product performance. Common ingredients names for these surfactants include the following: Laureth-23, Ceteareth-20, Quarternium-15, and Dimethyl Distearyl Ammonium Chloride to mention just a few. Manufacturers may also include alpha-hydroxy acids such as glycolic and lactic acid.12
The following table was created using the ingredient listings located on the backside of the bottles. It is presented in this format to further illustrate how many brands share common components. For simplicity, ingredients listed on only one of the five lotions do not appear in the table. Note that surfactants vary from product to product and may not be included in this list.
Table 1.
Common Components Present in Different Brands of Moisturizing Lotion*
Suave / Bath & Body / Bristol / The Andrew / Body BenefitsWorks / Meyers / Jergens Co.
Water / X / X / X / X / X
Glycerin / X / X / X / X / X
(Tetra, Tri, or Di-) sodium EDTA / X / X / X / X
Dimethicone / X / X / X / X / X
Carbomer / X / X / X
Tocopheryl Acetate (Vitamin E) / X / X / X
Aloe gel / X / X / X
Petrolatum / X / X / X / X
Glyceryl Stearate / X / X
Sodium Hydroxide / X / X
Methylparaben / X / X / X
DM DM Hydantoin / X / X
Benzyl Alcohol / X / X
Magnesium Aluminum Silicate / X / X
Propylparaben / X / X
Mineral Oil / X
Isopropyl palmitate / X / X
Cetyl Alcohol / X / X / X
Cetearyl Alcohol / X / X
Ceteareth-20 / X / X
* Components present in only 1 of the 5 lotions are not listed here.
The primary ingredient in most moisturizing lotions is de-ionized water. It can be expected that water comprises anywhere between 60 and 95 weight % of the lotion. Following is a graphical display of the composition of a particular formulation of moisturizing lotion taken from U.S. Patent # 6,017,548 assigned to The Andrew Jergens Company.12
Table 2.
Approximate Composition of a Lotion Patented byThe Andrew Jergens Company (U.S. Patent# 6,017,548)
Chart # / Components / Approx. % Weight
1 / Water / 93.2
2 / Glycerin / 2.4
3 / Dimethyl Distearyl Ammonium Chloride / 1
4 / Petrolatum / 0.8
5 / Lactic Acid / 0.6
6 / Isopropyl palmitate / 0.6
7 / Cetyl Alcohol / 0.5
8 / Glycolic Acid / 0.4
9 / Dimethicone / 0.3
10 / Ammonium Hydroxide / 0.2
11 / Methylparaben / 0.02
12 / Propylparaben / 0.008
Graph 1.
III. Colloids and Surface Interactions
Throughout the diverse moisturizing lotions that are sold today there exist common ingredients that perform key universal functions to moisturizing lotions. The most abundant of these ingredients is water, whether it is purified or deionized. Since moisturizing lotion is an oil-in-water emulsion, water is the continuous phase and functions as the diluent. Glycerin (C3H8O3) serves as the humectant, which adds moisture to the stratum corneum, which is the skin, and helps to soften the skin 12. Silicone fluids are also utilized in lotions as an emollient or smoothing aid. They improve the lubricity of the moisturizing lotion when it is applied to the skin 12. An example of a commonly used silicone fluid is Dimethicone (C2H6OSi). Petrolatum and/or mineral oil are added to the emulsion to serve as an occlusive emollient. These hydrocarbons form a hydrophobic film on the surface of the skin, which prevents water loss from the skin to the environment. It traps the moisture in the skin. Disodium EDTA functions as the chelating agent 16, and carbomer, a carboxyvinyl polymer, acts as a thickening and emulsifying agent. A key difference among various lotions is the type of surfactant/emulsifier used. Despite the use of different emulsifiers the basic the function of the amphiphile remains the same, which is to stabilize the oil-in-water emulsion by acting at the oil-water interface. One example of the surfactant used in Keri Fragrance Free Lotion is Quaternium-15, which is a cationic emulsifier.
In addition to the universal ingredients, many other molecules become a part of lotion. These might include fatty alcohols such as cetyl alcohol, which combined with the surfactant aid in stabilizing the emulsion 5. Further examples include nutrients such as tocopheryl acetate (Vitamin E), preservatives, and fragrances. Some of these components, for Keri Fragrance Free Lotion, along with their basic functions are shown below in Table 3.21
Table 321
KERI FRAGRANCE FREE LOTIONComponent / Basic Function
Water / diluent
Glycerin / humectant
Dimethicone * / emollient, smoothing aid
Petrolatum * / occlusive emollient
Disodium EDTA / chelating agent
Carbomer * / thickening agent, emulsifying agent
Quaternium-15 * / cationic surfactant, cationic emulsifier
Cetyl Alcohol * / emollient, emulsion modifier, coupling agent
Tocopheryl Acetate (Vitamin E) * / nutrient
Steareth-2 * / emulsifier, wetting agent
Aloe gel / nutrient
Benzyl Alcohol / antimicrobial
Laureth-23 * / emulsifier, wetting agent
Magnesium Aluminum Silicate / thickening agent
Sodium Hydroxide / alkalizer, pH adjuster
* = "colloidal" sized molecules
A. Liquid/ Liquid Emulsion
Moisturizing lotion is a liquid-liquid emulsion. An emulsion is formed when a mixture of two immiscible liquids are separated by a surfactant molecule, which lines the interface of the liquids. The surfactants are amphiphilic molecules composed of a hydrophilic polar headgroup and a “hydrophobic” nonpolar tail. When placed into an oil-water solution, the amphiphiles spontaneously aggregate at the oil-water interface to minimize unfavorable interactions. They do so by orienting themselves in such a manner that their headgroups point into water while their nonpolar tails point into the oil. In a microemulsion of oil-in-water, O/W, the surfactants form droplets of oil in water. Likewise a microemulsion of water droplets in oil, W/O, can also be attained, where the surfactant headgroups point into the water and the nonpolar tails face outward into the oil. Depictions of an O/W (a) and W/O (b) microemulsion are shown below in figure 1. below 1.
Figure 1
Moisturizing lotion is an oil-in-water, O/W, emulsion. However, the process of making lotion begins with a W/O emulsion. During the mixing procedure, a phase inversion occurs changing W/O to O/W. There are at least three possible factors that can be altered to achieve this phase inversion. They are: (1) temperature, (2) surfactant composition, and (3) water concentration.
The temperature of the emulsion can lead to a phase inversion if temperature sensitive emulsifiers, such as ethoxylate emulsifiers, are used as surfactants 9. Ethoxylate emulsifiers become less hydrophilic when heated. Therefore, emulsions that use them change achieve a reversible phase inversion from O/W to W/O at a well-defined temperature, called the phase inversion temperature (PIT). “Cosmetics O/W emulsions with improved stability and small droplet size can be manufactured by producing a W/O emulsion at high temperature and cooling through a phase inversion” 9. This technique of varying the emulsion temperature only leads to a phase inversion if ethoxylated surfactants are used. This is because other types of surfactants do not show a significant sensitivity to temperature change 9.
The surfactant composition in the emulsion can also be altered in order to achieve a phase inverse. For example, consider a W/O emulsion that is generated using a hydrophobic emulsifier and to which is added an aqueous solution of hydrophilic surfactant. At low hydrophilic surfactant concentration the system remains as a W/O emulsion. However, as the hydrophilic concentration increases, the system will eventually undergo a phase inversion from a W/O to an O/W emulsion 9.
Finally, a third variable that can lead to a phase inversion is the water concentration in the emulsion. Starting with a W/O emulsion, if a sufficient amount of water is added to the system, a catastrophic phase inversion will occur resulting in an O/W emulsion 9. This is the technique by which the Andrew Jergens Company prepares moisturizing lotion:
The oil-in-water emulsions of this invention are prepared by first forming an aqueous mixture of the water-insoluble component and the humectant. The water-insoluble components include the cationic emulsifier, the petrolatum or mineral oil component, the fatty alcohol component, the fatty ester emollient, and the silicone component. The components are preferably added to water in the following sequence: humectant, petrolatum/mineral oil, fatty ester, silicone oil, fatty alcohol. After these components are thoroughly mixed, the cationic emulsifier is added to the aqueous moisture at a temperature of about 80 to 95 degree C. under agitation to form a water-in-oil emulsion. The input of the mixing energy will be high and will be maintained for a time sufficient to form a water-in-oil emulsion having a smooth appearance (indicating the presence of relatively small micelles in the emulsion). Water is then directly injected into the emulsion to cool it to a temperature of about 45 to about 60 degree C. The temperature is critical. Unstable emulsions result if the temperature drops below about 45 degree C. Higher temperatures promote unacceptable water loss through evaporation. During this quench step the emulsion, initially water-in-oil, inverts to form an oil-in-water emulsion.12
B. The Effect of Amphiphiles on Delivery to the Skin
One type of surfactant used in moisturizing lotions is the cationic surfactant; positively charged molecules in solution. The behavior of ionic micelles can be explained by ‘hydrophobic’ tail and headgroup characteristics. As the temperature of the emulsion increases, the critical surfactant concentration for micelle formation (CMC) increases and the number of amphiphile molecules per micelle (No) decreases. The increase in temperature leads to a greater repulsion between headgroups, resulting in a higher Gel, a higher Gmic, and an increase in CMC. 1 Gel is the free energy associated with purely electrostatic interactions arising from headgroup repulsions. Gmic is the free energy of micelle formation. Ultimately, the increase in temperature decreases the stability of the emulsion by decreasing the stability of the micelles. Furthermore, the addition of salt lowers the CMC while increasing the No. Adding salt has the opposite effect on ionic micelles than raising the temperature. 1
The effect of temperature on ionic micelles may also effect the mechanism of moisturizing lotion on the skin. While the exact mechanism is not entirely understood, it is believed that the temperature change that occurs when the lotion is applied to the skin induces a phase change; causing the humectant (glycerin) to move from the micellular interface to the external surface of the emulsion. The humectant is then able to transfer to the stratum corneum in order to moisturize the skin12. Perhaps the higher temperature of the skin destabilizes the micellular structure, releasing the humectant inside.
Cationic surfactants are not the only type of emulsifiers that are used to prepare moisturizing lotion. For example Noveon has formulated a moisturizing lotion with Pemulen polymeric emulsifiers. Pemulen emulsifiers have the ability to form long-term stable O/W emulsions that have a triggered release mechanism. “Pemulen emulsifiers instantly deswell upon contact with the electrical charge on the skin to release the oil phase and provide immediate coverage, eliminating the lengthy lag time seen using traditional surfactant systems.”16 In traditional surfactant systems liquid crystals made up of oil, water, and surfactant are formed and are deposited on the stratum corneum. These liquid crystals temporarily prohibit the oil phase from being released to the skin so that it cannot form a desired occlusive film. The crystals can last for up to 90 minutes before they are degraded due to the evaporation of water from the liquid crystals to the environment. An illustration is shown below, Figure 2, comparing the application of traditional surfactant systems to emulsions formulated with Pemulen polymeric emulsifiers. 16
Figure 2
Unlike cationic surfactants, Pemulen appears to be electrically sensitive rather than temperature sensitive. Cationic surfactants and Pemulen are examples of how the use of different surfactants directly influences the mechanism by which moisturizing lotion aids the skin.
IV. Product Attributes
The colloids, polymers, and surfactants enhance and affect the product specifications. Each ingredient serves at least one purpose. Many of the ingredients have multiple purposes. For the four chosen moisturizing lotions one can see the similar components. Water is the main component of lotion and its main purpose to serve as a diluent. Dimethicone, Glycerine, EDTA, and Carbomer serve many different basic functions for example as emollients, humectants, chelating agents, and thickening agents. In Table 3 Keri fragrance free lotion shows its main functions of its ingredients.
Some examples of colloids and polymers that enhance the affect the product specification are described. Dimethicone is a silicone fluid mixture that enhances the durability, gives a nice soft feeling and is also an anti-whitening agent. It gives the skin a pleasant shine. Laureth-23 is a non-ionic emulsion that is often used as a conditioning agent in lotions. It gives skin luxurious feeling when applied. Fatty acids such as Benzyl or cetearyl alcohol thicken and stabilize the lotion. 5
The functionality of primary ingredients in relation to customer needs is one of the most important characteristics of lotion. The lotion’s shelf life, absorption properties, consistency, and fragrance are altered through different colloids, polymers, and surfactants. Also sunscreens, alpha hydroxide, slow release of fragrances, and prolonged hydration properties are achieved by different colloidal particulate systems.8
The shelf life of moisturizing lotion is extremely important. A company can estimate the amount of time it takes for a bottle to be bought. Once the bottle is bought it could take up to a year to finish and it all depending on the amount of lotion in the bottle. Bigger bottles of lotion are much more economically efficient, but no one would buy the lotion if it were going to go “bad”. This is why the shelf life is such a crucial part of lotion. Adjusting the hyrdophile and lipophile balance of the emulsifier is a very important aspect for achieving emulsion stability. 12 Emulsions prepared with hydrophobically modified water-soluble polymers are stable for years. The lotion’s dermatological emulsions are thermodynamically unstable due to its positive interfacial energy. When the emulsion tries to reach its thermodynamic equilibrium it causes the emulsion to break up back into its component phase. In order for the product to be able sustain it shelf life qualities, the formula must attempt to delay the separation process. The delay can be accomplished by adding specific mixed emulsions compiled of ionic or non-ionic surfactants combined with fatty amphiphiles (Table 4). 5