This is a guest post by Gary Neudahl. He is currently Product Application Manager, Personal Care Ingredients, for the HallStar Company and is based at the HallStar Manufacturing and Technical Center in Bedford Park IL USA.
In this second article in the series, we move from the underarm area to general skin care. Product application areas may include the feet, legs, genitals, breasts, trunk, arms, hands, cuticles, neck, face, eye area, scalp, or entire body. Product forms include emulsions such as milks, lotions, creams, soufflés and butters; liquids, as solutions, sera, mists, or sprays; semi-solids like gels, sticks, balms or ointments; and solids, including powders.
The benefits of topically applied products are often not entirely cosmetic. Active ingredients may be incorporated to provide any of a variety of benefits including, among others, sun protection, pain relief (analgesics or anesthetics), itch relief (anti-inflammatories), redness (“erythema”) reduction, age spots reduction (e.g., fade creams), acne treatment, and fungal and/or bacterial infection prevention or treatment.
Hand and body lotion
With all these possibilities, what will we examine today? The ubiquitous hand & body lotion. Whether the lotion is a well-known brand name or a new introduction, natural or organic, luxury or value priced, it is going to contain certain components core components, and will often have more:
Emollients 5 — 20%
Emulsifiers 2 — 7%
Humectants 2 — 5%
Stabilizers 0.1 — 2%
Preservatives 0.1 — 1%
Feel Modifiers 0 — 2%
Protectants 0 — 1+%
pH-Adjusting 0 — 1%
Chealants 0 — 0.1%
Antioxidants 0 — 0.1%
Fragrance q. s.
Colorants q .s.
Water to 100%
Emollients are substances that are used to correct or mask skin dryness and scaling. They are typically oil soluble and make skin look and feel smoother. Emollients are often grouped according to their longevity and intensity of effect. Those that are volatile or are absorbed rapidly into the skin, and so provide only a transient effect, are termed very light, dry emollients. These include Cyclopentasiloxane and esters such as Ethylhexyl Isononanoate and Diisobutyl Adipate. Light emollients are typically slightly more viscous and have a light oily to cushiony feel on skin. Examples include light mineral oil and Butyloctyl Salicylate. Heavy emollients are viscous liquids or semi-solids that penetrate the skin slowly and that are often occlusive (trap moisture within the skin). The best known examples may be Petrolatum and Lanolin. Waxy emollients may be included as feel modifiers (see below). They include fatty alcohols such as Cetearyl Alcohol and fatty esters such as Cetyl Palmitate.
Humectants are substance that have an affinity for water and so increase the water-holding capacity of skin. They are also included to improve finished product freeze-thaw stability, which is very important in frigid climates. The gold standard for humectancy is Glycerin. Because of the high degree of tack it imparts to skin on its own, it is often combined with one or more glycols, such as Butylene Glycol, to reduce the tackiness to an unobjectionable level.
Emulsifiers are surfactants that, when appropriately selected, align at the interface of two immiscible liquids (e.g., oil and water). Put under shear, a quasi-stable dispersion of droplets of one of the liquids in the other, called an emulsion, is formed. As is common for emulsions in general, hand and body lotions typically use a combination of both oil-loving (low hydrophilic-lipophilic balance = HLB) and water-loving (high HLB) emulsifiers to achieve optimal stability. The vast majority of hand and body lotions marketed in the USA are oil-in-water (O/W) emulsions. This makes a lot of sense because water, which is both inherently nonoily and low cost, is the primary component and the continuous phase. Probably the most commonly utilized low HLB emulsifier is Glyceryl Stearate. Frequently utilized high HLB emulsifiers include PEG-100 Stearate, Potassium Stearate and in situ formed TEA-Stearate. At near neutral pH these Stearate salts also contribute liquid crystalline structure to the emulsion, markedly enhancing its stability.
Emulsion stabilizers are materials added to extend the shelf-life of the lotion by preventing creaming, settling, and coalescence of the droplets that have been suspended in the continuous phase. As mentioned earlier, Stearate soaps function in this capacity, in addition to being high HLB emulsifiers. The most commonly utilized emulsion stabilizers are water swellable polymers that form a matrix of high yield value, yet low viscosity under shear. The gold standard in this area is Carbomer, with modified polyacrylates and polyacrylamides also commonly utilized.
Preservatives (antimicrobials) are incorporated to reduce the risk of microbial contamination of the lotion during manufacture, storage and use. Among those commonly used globally is Phenoxyethanol with various parabens or Caprylyl Glycol. For those interested in a preservative-free positioning, specially selected botanical extracts and/or essential oils may be used.
Other components that are often present include feel modifiers. Although almost all components of a hand & body lotion contribute to the feel of the product on the skin during application and/or after drydown, feel modifiers may be added to affect specific attributes. For example, Aluminum Starch Octenylsuccinate may be added to reduce oiliness, while Cetearyl Alcohol may be added to impart a richer, thicker, waxier feel, as well as to increase opacity.
The monographed skin protectant most commonly utilized in hand & body lotions is Dimethicone. It is relatively low cost, has a low required use level, is essentially odorless and colorless, and can also improve the spreadability and reduce the whitening of the lotion during rub-in.
The rest of the ingredients
The most commonly used pH adjusting agent is probably Triethanolamine, which can be used to neutralize Stearic Acid that has been incorporated as part of the oil phase, as well as polyacrylates such as Carbomer that have been added to improve shelf-stability. As a weak base (in comparison to Potassium Hydroxide), its addition late in the batching process is less likely to induce localized emulsion inhomogeneity.
Chelants, such as Disodium EDTA, may be used to tie up multivalent ions that become part of the composition. These ions may promote both the oxidation of unsaturated ingredients and the growth of microorganisms. By inactivating metal ions, chelants enhance fragrance stability and microbiological integrity, and so extend product shelf life.
Antioxidants such as Tocopherol or BHT may be added as an alternative, or as a supplement, to the stabilizing effects of chelants. The intent is to extend shelf life by reducing oxidative processes.
Fragrance (parfum) is frequently added, if for no other reason than to mask the base odor of the product. When a signature fragrance is part of the market positioning for the lotion, up to about 2% fragrance may be present. When hypoallergenic and/or “no fragrance” claims are made for the product, carefully selected essential oils, botanical extracts and/or individual synthetic chemicals may be added to control product odor without needing to use the word “fragrance” on the label.
Colorants, most commonly water soluble, may be added at very low level for their esthetic benefits.
And that’s it until next month! If you have additional questions, you may contact the author at firstname.lastname@example.org.