The chemistry of skin cleansers: an overview for clinicians.
The techniques and agents used to cleanse the skin are important factors in the maintenance and restoration of the skin barrier or, conversely, in causing and continuing damage to the stratum corneum and its important barrier functions. In addition to barrier maintenance issues, recommendations for skin-cleansing practices should take into consideration individual patient characteristics, including age, gender, and any underlying skin conditions, as well as cultural and personal preferences regarding aesthetics (including the fragrance of products). As examples, individuals with dry skin should use a cleanser that minimizes further drying, and those with eczema or other skin conditions should use nondrying cleansers that may also replenish lipids. In this article, we provide an overview of the goal of skin cleansing, how skin cleansers work, and the ingredients commonly used in cleansers that are important to remember in clinical practice.
Overview of Skin Cleanser Ingredients
Skin cleanser chemistry is not an esoteric topic and does not require in-depth study for clinicians to acquire the necessary foundation for making informed and appropriate recommendations to patients that are tailored to their individual needs. In addition to water (included in almost all skin cleansers), the ingredients also include surfactants, along with any of a number of other possible ingredients such as antimicrobial agents to reduce bacterial colonization, viscosity enhancers that affect the feel of a product (found mainly in shampoos), moisturizers, preservatives, and fragrances (Table 1).
Briefly stated, a surfactant--a term derived from the words "surface" and "active"--is a cleansing agent. The earliest known surfactants were soaps consisting of sodium or potassium salts of fats or fatty acids. Until about the middle of the 20th century, soaps used for bathing were largely crude formulations of a lipid such as tallow (ie, rendered animal fat) plus lye (a strongly alkaline solution usually derived from wood ash). Improvements in these lye-containing formulations were made by substituting various sulfates (such as sodium lauryl sulfate) and carboxylates. The benefit of these earlier generations of soaps was that they were essentially nonallergenic. However, the simple, small long-chain molecules that comprised these soaps tended to cause stinging, burning, and irritation, particularly when used on sensitive skin or when accidentally splashed into the eyes. Also, these types of simple soaps (which are still widely available today) may increase xerosis and worsen the skin condition in patients with eczema.
In today's skin cleansers, a variety of newer surfactants are used (Table 2). These include amphoteric compounds (chiefly, cocamidopropyl betaine, plus others in the betaine family, and related compounds), nonionic compounds (such as cocamide diethanolamine, also called cocamide DEA), and hydrophobically modified (HM) polymers.
Surfactants are molecules with both a hydrophilic and a hydrophobic region: The hydrophobic component scavenges oils, soil, and other contaminants from the skin; the hydrophilic component allows their removal from the skin by rinsing with water.
In an aqueous solution, surfactants naturally self-organize into groups called micelles. Research has shown that micelle size negatively correlates with irritancy--that is, the larger the micelles, the less irritating the surfactant, because the larger molecules are less able to penetrate the stratum corneum. Product research over the past 5 to 6 decades have yielded methods of chemically altering surfactants to create larger micelles, including ethoxylation and, more recently, pegylation using polyethylene glycol. The largest micelles developed to date are in the HM-polymer surfactant, created by linking groups of micelles together using a polymerizing component.
Some cleansers--especially some of the newer hand cleansers and products used in medical and dental offices and hospitals, for example--may contain antimicrobial ingredients. These may include various alcohol formulations and agents such as benzalkonium chloride and iodine solutions.
These agents are not usually found in products that are intended for use in infants and children or for anyone with sensitive skin, although occasionally they are seen in such products. These chemicals tend to be irritating and, in some cases, can be allergenic.
Many cleansers contain moisturizers to reduce the potentially irritating and drying effects of the other ingredients. Some cleansing products claim that the moisturizers they contain remain on the skin following rinsing; this may be true for some moisturizing ingredients in some cleanser formulations, but it is difficult to determine how much of the moisturizer actually persists. Glycerin, lanolin, various lipids, and petrolatum are commonly used.
Preservatives are almost always included in the formulation of any water-based system to prevent bacterial and fungal growth. Ideally, preservatives should be hypoallergenic and active against a broad range of microorganisms. Few preservatives fulfill both of these requirements, so often combinations of preservatives are used.
Fragrances add to the aesthetic appeal of skin care products and are ingredients in most cleansers, moisturizers, and other products. An entire industry is devoted to the chemistry, psychology, development, and manufacture of fragrances.
The physiology and psychology of smell explains why almost all personal care products contain fragrances. Olfactory receptors communicate with the brain's most ancient center, the limbic system. (1,2) So strong is the olfactory experience that memories of events or objects are associated with an individual's exposure to pleasant or unpleasant odors; subsequent exposure to the smell--pleasant or unpleasant--often evokes a memory of the event or object or with the feeling associated with the event. (2-4) Smells are associated with autobiographical episodes. (5) In fact, memories triggered by odors tend to be more emotional than are those evoked by visual or auditory cues. (6) Human language that describes olfactory stimuli reflects the emotional response to those stimuli: "Odor" usually denotes a less-than-pleasant smell; scent, fragrance, and aroma are synonyms for pleasant smells.
Primarily because of these emotional responses, non-scented products are preferred over those with a smell that is perceived as unpleasant, and pleasantly scented products tend to be preferred over unscented ones. (7) Studies have shown that fragrances in skin care products can have positive emotional associations, resulting in an improved mood and a heightened overall sense of well-being. (8,9) Sometimes fragrances even suggest better product efficacy (1,7)--for example, when certain fragrances are perceived as having a "clean scent" or a "fresh scent," implying more effective cleansing properties.
A relatively frequent skin complaint is dermatitis resulting from allergy to a skin cleanser. Many patients who complain of an "allergy" to skin care products actually are experiencing an irritant reaction, but true allergy does occur. Among the cleanser category of skin care products, preservatives and fragrances represent the most common allergens; surfactants and moisturizing additives can be allergenic, but this is not as common as fragrance and preservative allergy.
An allergic reaction to a facial cleanser or shampoo typically is seen on the face--especially the eyelids (Figure)--and sometimes the neck. The scalp, which appears to be more resistant to allergen penetration, is rarely affected, even with shampoo allergies. If an individual is allergic to a cleanser, the intertriginous areas also are affected, if exposed (as in the shower or bath).
Preservative Allergenicity and Irritancy
From the standpoint of allergenicity and efficacy, parabens are close to ideal. In contrast, a variety of preservatives are used that are formaldehyde based, although the term formaldehyde is not listed on the cleanser label as an ingredient. These preservatives have some direct antimicrobial effect, but they also work by slowly degrading in solution and releasing small amounts of formaldehyde. The formaldehyde-based preservatives are very effective antibacterial and antifungal agents, but they tend to be allergenic.
Fragrance Allergenicity and Irritancy
Chemically, fragrances can consist of simple single molecules, but they usually consist of mixtures of dozens to hundreds of different molecules. Among the more than 1,000 fragrance chemicals in use are, of course, some allergens.
Professional perfumers are skilled at mixing the various chemicals to achieve a desired scent in everything from floor cleaners to floral room deodorizers. When fragrances are developed for products used on the skin, the goal is to achieve the desired scent using fragrance ingredients that are least likely to be allergenic. However, as with all chemicals to which skin may be exposed, individual sensitivities may result in allergic reactions to even those that might be considered "nonallergenic" or "hypoallergenic" fragrances.
Fragrances also can be irritants, and it may be prudent to recommend that individuals with diseases (such as atopic dermatitis) or very sensitive skin avoid products with fragrances, even if there is no allergy.
The newer surfactants (described in a previous section) are milder to the skin and eyes but tend to be more allergenic than some of the earlier compounds. Although surfactant allergies are not common, those that are seen usually occur with exposure to cocamidopropyl betaine and related compounds.
Diagnosing Allergies to Skin Cleansers
Sometimes when patients experience allergic reactions to a skin care product, they self-treat by changing brands. However, many of the same ingredients--particularly surfactants and preservatives--are used in different types from different manufacturers, and unless the new product does not contain the allergenic compound, the reaction will persist. Patch testing often is necessary to identify a specific allergen so that a patient knows which particular ingredients to avoid when choosing cleansers or other skin care products.
The use of cleansers is a necessary and beneficial part of good skin care throughout life. Because both allergic and irritant contact dermatitis may be caused by components of skin cleansers, it is important for clinicians to be aware of and understand the nature and functions of the ingredients listed on skin care product labels. Fragrances, preservatives, and surfactants are the components usually implicated when contact dermatitis does occur.
Surfactants that are associated with the formation of larger, rather than smaller, micelles are less likely to be irritating to individuals with sensitive skin. The newer surfactants, designed for infant skin and individuals with eczema, are in this category. Products containing preservatives that break down into formaldehyde are more likely to be allergenic in sensitive individuals. Parabens are among the compounds that are not formaldehyde based and are relatively hypoallergenic.
(1.) Van Toiler S, Dodd GH, eds. Perfumery: The Psychology and Biology of Fragrance. New York, NY: Chapman and Hall; 1988; chap 11.
(2.) Gottfried JA, Deichmann R, Winston JS, Dolan RJ. Functional heterogeneity in human olfactory cortex: An event-related functional magnetic resonance imaging study. J Neurosci. 2002;22:10819-10828.
(3.) Gottfried JA, Smith AP, Rugg MD, Dolan RJ. Remembrance of odors past: Human olfactory cortex in cross-modal recognition memory. Neuron. 2004;42:687-695.
(4.) Bensafi M, Sobel N, Khan RM. Hedonic-specific activity in piriform cortex during odor imagery mimics that during odor perception. J Neurophysiol. 2007; 98:3254-3262.
(5.) Larsson M, Willander J. Autobiographical odor memory. Ann N Y Acad 5ci. 2009;1170:318-323.
(6.) Herz RS. A naturalistic analysis of autobiographical memories triggered by olfactory visual and auditory stimuli. Chem Senses. 2004;29:217-224.
(7.) Bone PF, Jantrania 5. Olfaction as a cue for product quality. Math Lett. 1992; 3:289-296.
(8.) Knasko SC. Pleasant odors and congruency: Effects on approach behavior. Chem Senses. 1995;20:479-487.
(9.) Warren C, Warrenburg S. Mood benefits of fragrance. Perfumer Flavorist. 1993; 18:9-16.
Caption: Figure. Allergic reaction. This patient had a typical presentation of a shampoo allergy. The eyelids show a severe reaction, although the rest of the face is relatively unaffected. Photo courtesy of Joseph E Fowler, Jr, MD.
Joseph E Fowler, Jr, MD, * Lawrence E Eichenfield, MD, ([dagger]) Peter M. Elias, MD, [double dagger]) Paul Horowitz, MD, [section] and Renee P. McLeod, PhD, APRN-BC, CPNP ([parallel])
* Clinical Professor of Dermatology, Contact and Occupational Dermatology, University of Louisville, Louisville, KY.
([dagger]) Professor of Clinical Pediatrics and Medicine (Dermatology), University of California, San Diego, Chief, Pediatric and Adolescent Dermatology, Rady Children's Hospital, San Diego, CA.
([double dagger]) Professor Emeritus, Department of Dermatology, University of California, San Francisco, and Dermatology Service, VAMC, San Francisco, CA. Private Practice, Discovery Pediatrics, Inc., Valencia, CA.
([parallel]) Dean and Professor, Musco School of Nursing and Health Profession, Brandman University, Irvine, CA.
Publication of this CME article was jointly sponsored by the University of Louisville School of Medicine Continuing Medical Education and Global Academy for Medical Education, LLC, and is supported by an educational grant from Johnson & Johnson Consumer and Personal Products Worldwide, Division of Johnson & Johnson Consumer Companies, Inc.
The faculty have received an honorarium from Global Academy for Medical Education for their participation in this activity. They acknowledge the editorial assistance of Joanne Still, medical writer, and Global Academy for Medical Education in the development of this continuing medical education journal article. Joanne Still has no relevant financial relationships with any commercial interests.
Peter M. Elias, MD, has no relevant financial relationships with any commercial interests.
Lawrence F. Eichenfield, MD, has been an investigator and/or consultant for Galderma Laboratories, Stiefel a GSK company, and Valeant Pharmaceuticals International.
Joseph F. Fowler, Jr, MD, has been a consultant and/or speaker and/or investigator for 3M, Abbott Laboratories, Allerderm, Allergan, Amgen Astellas Pharma US, Inc, Centocor, Dermik, Dow Pharmaceutical Sciences, Inc., Eli Lilly and Company, Galderma Laboratories, L.E, GlaxoSmithKline, Johnson &Johnson Consumer Products Company, Medicis Pharmaceutical Corporation, Merck Pharmaceuticals, Merz Aesthetics, Novartis Pharmaceutical Corporation, OnSet, Promius, Pfizer, Quinnova, Ranbaxy, SmartPractice, Taisho, Taro, and Valeant Pharmaceuticals International.
Paul Horowitz, MD, FAAP, has been a speaker and/or consultant and/or researcher for Abbott Laboratories and Johnson & Johnson Consumer Personal Products Worldwide.
Renee E McLeod, PhD, APRN-BC, CPNP, FAANP has been a speaker and/or consultant for Johnson &Johnson Consumer Personal Products Worldwide.
Address reprint requests to: Joseph F. Fowler, Jr, MD, 3100 Boxhill Lane, Louisville, KY, 40222; 502-583-7546, firstname.lastname@example.org
Table 1. Skin Cleanser Components * Water * Surfactants--the cleansing agents * Antimicrobials--reduce colonization * Viscosity agents--enhance product "feel" * Moisturizers--reduce drying * Preservatives--affect shelf life * Fragrances--enhance aesthetic appeal Table 2. Newer Surfactants * Amphoteric surfactants (eg, cocamidopropyl betaine) * Noninic surfactants (eg, cocamidopropyl betaine) * Hydrophobically modified polymers
Please note: Illustration(s) are not available due to copyright restrictions.
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|Author:||Fowler, Joseph F., Jr.; Eichenfield, Lawrence F.; Elias, Peter M.; Horowitz, Paul; McLeod, Renee P.|
|Publication:||Family Practice News|
|Date:||Aug 1, 2013|
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