SURFACTANT SCIENCE SERIES
MARTIN J. SCHICK
New York, New York
FREDERICK M. FOWKES
1. Nonionic Surfactants, edited by Martin J. Schick (see also Volumes 19, 23, and 60)
2. Solvent Properties of Surfactant Solutions, edited by Kozo Shinoda (see Volume 55)
3. Surfactant Biodegradation, R. D. Swisher (see Volume 18)
4. Cationic Surfactants, edited by Eric Jungermann (see also Volumes 34, 37, and 53)
5. Detergency: Theory and Test Methods (in three parts), edited by W. G. Cutler and R. C.
Davis (see also Volume 20)
6. Emulsions and Emulsion Technology (in three parts), edited by Kenneth J. Lissant
7. Anionic Surfactants (in two parts), edited by Warner M. Linfield (see Volume 56)
8. Anionic Surfactants: Chemical Analysis, edited by John Cross (out of print)
9. Stabilization of Colloidal Dispersions by Polymer Adsorption, Tatsuo Sato and Richard
Ruch (out of print)
10. Anionic Surfactants: Biochemistry, Toxicology, Dermatology, edited by Christian
Gloxhuber (see Volume 43)
11. Anionic Surfactants: Physical Chemistry of Surfactant Action, edited by E. H. Lucassen-
Reynders (out of print)
12. Amphoteric Surfactants, edited by B. R. Bluestein and Clifford L. Hilton (see Volume
13. Demulsification: Industrial Applications, Kenneth J. Lissant (out of print)
14. Surfactants in Textile Processing, Arved Datyner
15. Electrical Phenomena at Interfaces: Fundamentals, Measurements, and Applications,
edited by Ayao Kitahara and Akira Watanabe
16. Surfactants in Cosmetics, edited by Martin M. Rieger (out of print)
17. Interfacial Phenomena: Equilibrium and Dynamic Effects, Clarence A. Miller and P.
18. Surfactant Biodegradation: Second Edition, Revised and Expanded, R. D. Swisher
19. Nonionic Surfactants: Chemical Analysis, edited by John Cross
20. Detergency: Theory and Technology, edited by W. Gale Cutler and Erik Kissa
21. Interfacial Phenomena in Apolar Media, edited by Hans-Friedrich Eicke and Geoffrey
22. Surfactant Solutions: New Methods of Investigation, edited by Raoul Zana
23. Nonionic Surfactants: Physical Chemistry, edited by Martin J. Schick
24. Microemulsion Systems, edited by Henri L. Rosano and Marc Clausse
25. Biosurfactants and Biotechnology, edited by Naim Kosaric, W. L. Cairns, and Neil C. C.
26. Surfactants in Emerging Technologies, edited by Milton J. Rosen
27. Reagents in Mineral Technology, edited by P. Somasundaran and Brij M. Moudgil
28. Surfactants in Chemical/Process Engineering, edited by Darsh T. Wasan, Martin E.
Ginn, and Dinesh O. Shah
29. Thin Liquid Films, edited by I. B. Ivanov
30. Microemulsions and Related Systems: Formulation, Solvency, and Physical Properties,
edited by Maurice Bourrel and Robert S. Schechter
31. Crystallization and Polymorphism of Fats and Fatty Acids, edited by Nissim Garti and
32. Interfacial Phenomena in Coal Technology, edited by Gregory D. Botsaris and Yuli M.
33. Surfactant-Based Separation Processes, edited by John F. Scamehorn and Jeffrey H.
34. Cationic Surfactants: Organic Chemistry, edited by James M. Richmond
35. Alkylene Oxides and Their Polymers, F. E. Bailey, Jr., and Joseph V. Koleske
36. Interfacial Phenomena in Petroleum Recovery, edited by Norman R. Morrow
37. Cationic Surfactants: Physical Chemistry, edited by Donn N. Rubingh and Paul M.
38. Kinetics and Catalysis in Microheterogeneous Systems, edited by M. Grätzel and K.
39. Interfacial Phenomena in Biological Systems, edited by Max Bender
40. Analysis of Surfactants, Thomas M. Schmitt
41. Light Scattering by Liquid Surfaces and Complementary Techniques, edited by
42. Polymeric Surfactants, Irja Piirma
43. Anionic Surfactants: Biochemistry, Toxicology, Dermatology. Second Edition, Revised
and Expanded, edited by Christian Gloxhuber and Klaus Künstler
44. Organized Solutions: Surfactants in Science and Technology, edited by Stig E. Friberg
and Björn Lindman
45. Defoaming: Theory and Industrial Applications, edited by P. R. Garrett
46. Mixed Surfactant Systems, edited by Keizo Ogino and Masahiko Abe
47. Coagulation and Flocculation: Theory and Applications, edited by Bohuslav Dobias *
48. Biosurfactants: Production · Properties · Applications, edited by Naim Kosaric
49. Wettability, edited by John C. Berg
50. Fluorinated Surfactants: Synthesis · Properties · Applications, Erik Kissa
51. Surface and Colloid Chemistry in Advanced Ceramics Processing, edited by Robert J.
Pugh and Lennart Bergström
52. Technological Applications of Dispersions, edited by Robert B. McKay
53. Cationic Surfactants: Analytical and Biological Evaluation, edited by John Cross and
Edward J. Singer
54. Surfactants in Agrochemicals, Tharwat F. Tadros
55. Solubilization in Surfactant Aggregates, edited by Sherril D. Christian and John F.
56. Anionic Surfactants: Organic Chemistry, edited by Helmut W. Stache
57. Foams: Theory, Measurements, and Applications, edited by Robert K. Prud'homme
and Saad A. Khan
58. The Preparation of Dispersions in Liquids, H. N. Stein
59. Amphoteric Surfactants: Second Edition, edited by Eric G. Lomax
60. Nonionic Surfactants: Polyoxyalkylene Block Copolymers, edited by Vaughn M. Nace
61. Emulsions and Emulsion Stability, edited by Johan Sjöblom
62. Vesicles, edited by Morton Rosoff
63. Applied Surface Thermodynamics, edited by A. W. Neumann and Jan K. Spelt
64. Surfactants in Solution, edited by Arun K. Chattopadhyay and K. L. Mittal
65. Detergents in the Environment, edited by Milan Johann Schwuger
66. Industrial Applications of Microemulsions, edited by Conxita Solans and Hironobu
67. Liquid Detergents, edited by Kuo-Yann Lai
68. Surfactants in Cosmetics: Second Edition, Revised and Expanded, edited by Martin M.
Rieger and Linda D. Rhein
69. Enzymes in Detergency, edited by Jan H. van Ee, Onno Misset, and Erik J. Baas
ADDITIONAL VOLUMES IN PREPARATION
StructurePerformance Relationships in Surfactants, edited by Kunio Esumi and Minoru
Powdered Detergents, edited by Michael S. Showell
Surfactants in Cosmetics
Second Edition, Revised and Expanded
Martin M. Rieger
M & A Rieger Associates
Morris Plains, New Jersey
Linda D. Rhein
Johnson & Johnson Consumer Products
Skillman, New Jersey
Preface to the Second Edition
The need for surfactants in consumer acceptable cosmetic products formed the stimulus
for the preparation of the first edition of Surfactants in Cosmetics ten years ago. Since
that time much progress has been made in creating novel surfactants for the personal
care industry and in understanding the fundamental behavior of surfactants in solution
and their interactions with skin. More importantly, there has been steady movement
toward the selection of surfactants for cosmetics that have no objective adverse impact
on human skin and elicit noor at most minimalnegative subjective reaction. Thus, this
second edition not only reflects the search for milder surfactants but also presents up-to-
date information on the activity of mixtures that interact in solution and on the skin to
enhance perceived as well as absolute safety. In addition, this edition updates the
everchanging nomenclature of surfactants in the cosmetic industry and relies on
International Nomenclature Cosmetic Ingredient (INCI) names and designations, as
provided in the sixth edition of the International Cosmetic Ingredient Dictionary (available
from the Cosmetics, Toiletries, and Fragrance Association in Washington, D.C.).
The editors determined early on that the scientific information presented in the first
edition of Surfactants in Cosmetics remains valid. In order to avoid unnecessary repetition
and unwanted redundancy, the editors decided to depend primarily on a new set of
authors and to select alternative topics for the second edition. As a result, the second
edition provides a unique and novel aspect of the topic of surfactants in cosmetics.
Readers are urged to view the second edition not as a replacement for the first but as an
extension and an addition. The table of contents from the first edition is therefore
included to assist readers in their endless search for information.
The first three chapters of this book address the fundamentals of surfactants, with
emphasis on their uses in cosmetics. These chapters provide the basic science required
for the effective use of surfactants.
Chapters 49 discuss the current status of research on the application of surfactants
in cosmetic emulsions. Chapters 1012 introduce the reader to microemulsions and
vesicles. These nine chapters are intended to help in the formulation of cosmetic
Chapters 1317 provide current information on surfactant usage in the formulation of
various types of cosmetic products, and chapters 1825 deal with the critical topic of the
interaction of surfactants with the skin. Chapters 1325 mayat timesappear to cover
similar topics, primarily because this material is of great interest and is often viewed from
The last three chapters cover topics of importance to practitioners which result from the
use of surfactants in cosmetic products.
The editors thank the authors for their contributions and for accepting our editorial
suggestions with alacrity. We regretfully note that Dr. Morton Pader passed away shortly
after submitting his contribution. The editors also recognize with deep appreciation the
help provided by the staff of the publisher.
As noted, the second edition differs materially from the first edition, and it is hoped that
readers will find the book useful and of current and continuing interest.
MARTIN M. RIEGER
LINDA D. RHEIN
Preface to the First Edition
The monetary value of worldwide sales of cosmetics and toiletries is extremely large;
however, the value of these consumer products might better be measured in terms of
their psychological and health benefits and their impact on our daily lives. Most modern
cosmetic preparations could not be produced without the use of a variety of surfactants,
and it is appropriate, therefore, to devote a volume to this topic in the Surfactant Science
The editor of a collective volume, such as this one, establishes the book's objectives,
which in turn determine its makeup and contents. It is the principal purpose of this
volume to provide a comprehensive survey of the use of surfactants in cosmetics. The
reader can expect to find specific information on all types of surfactants used in cosmetics
and toiletries and, equally important, references to the vast original literature on this
More specifically, the goal of this book is to provide answers to some pertinent questions
such as those listed below:
What surfactants are used in cosmetics?
Why are surfactants required in cosmetics?
What functions are served by surfactants in cosmetics?
How are surfactants used in cosmetics?
What problems are caused by the use of surfactants in cosmetics?
What interactions take place between surfactants in cosmetics and the substrate, i.e., the
skin and its appendages?
It should be noted that there are some omissions in this text; these are intentional. We
are attempting to avoid redundancy from chapter to chapter in this book and also within
the Surfactant Science series, which now includes about 21 books. Thus, details of the
complex chemistry of the surfactants are deliberately excluded since this subject is
expertly covered in other volumes in the series. Also avoided is the use of (the ever
changing) commercial or trade names for surfactants. Instead, the nomenclature
employed in the current issue (1982) of the CTFA Cosmetic Ingredient Dictionary is used
extensively. Last but not least, an effort is made not to create an assembly of recipes for
the preparation of cosmetic formulations; the few formulations included are presented
only for illustrative purposes.
The editor sincerely hopes that these goals have been achieved. The editor also hopes
that readers of the book will find it not only scientifically useful but readable as well.
Special thanks are due to the authors of the various chapters who have patiently endured
the need for editorial changes and the unavoidable delays incurred in a multi-authored
book. Thanks are also due the Cosmetic, Toiletries, and Fragrance Association which
granted permission to utilize CTFA surfactant nomenclature as well as many ingredient
descriptions from the Cosmetic Ingredient Dictionary. Finally, gratitude is expressed to
my faithful secretaries, Ms. G. Pilewski and Ms. G. Salmon, and to the editorial staff of
Marcel Dekker without whose help this book could not have been produced.
MARTIN M. RIEGER
Contents of the Second Edition
Preface to the Second Edition iii
Preface to the First Edition v
Contents of the First Edition xi
1. Surfactant Chemistry and Classification
Martin M. Rieger
2. Physical Properties of Surfactants Used in Cosmetics
3. The Analysis of Surfactants in Cosmetics
Jane M. Eldridge
4. Principles of Emulsion Formation
5. Emulsifier Selection/HLB
Donald L. Courtney, Sr.
6. Multiple Emulsions in Cosmetics
Monique Seiller, Francis Puisieux, and J. L. Grossiord
7. Multiphase Emulsions
H. E. Junginger
8. Stability of Emulsions
Christopher D. Vaughan
9. Phase Inversion in Emulsions: CAPICOConcept and
Armin Wadle, Holger Tesmann, Mark Leonard, and Thomas
10. Solubilization in Cosmetic Systems
Stig E. Friberg and Jiang Yang
11. Selection of Solubilizers
Francesc Comelles and Carles Trullás
12. Liposomes and Niosomes
Daniel D. Lasic
13. Surfactants for Skin Cleansers
14. Cleansing Bars for Face and Body: In Search of Mildness
Richard I. Murahata, M. P. Aronson, Paul T. Sharko, and Alan
15. Topical Antibacterial Wash Products
Boyce M. Morrison, Jr., Diana D. Scala, and George E.
16. Hair Cleansers
17. Surfactants in Dental Products
18. In Vitro Interactions: Biochemical and Biophysical Effects
of Surfactants on Skin
Linda D. Rhein
19. Surfactant Mildness
20. Surfactant Effects on Skin Barrier
21. Bioengineering Techniques for Investigating the Effects
of Surfactants on Skin
Perveen Y. Rizvi, Gary L. Grove, and Boyce M. Morrison, Jr.
22. Skin Penetration Enhancement by Surfactants
Joel L. Zatz and Belinda Lee
23. Human in Vivo Methods for Assessing the Irritation
Potential of Cleansing Systems
F. Anthony Simion
24. The Challenge of Using the ''Inarticulate" Consumer As
an R & D Partner in Cosmetic Product Development
David W. Ingersoll
25. Toxicology of Surfactants Used in Cosmetics
26. Chemical Instability of Surfactants
Martin M. Rieger
27. Inactivation of Preservatives by Surfactants
Donald S. Orth
28. Solubilization of Fragrances by Surfactants
John N. Labows, John C. Brahms, and Robert H. Cagan
Contents of the First Edition
1. Surfactants for Cosmetic Macroemulsions: Properties and
2. Microemulsions and Application of Solubilization in
T. Joseph Lin
3. Surfactant Association Structures of Relevance to
Stig E. Friberg and Magda A. El-Nokaly
4. Low-Energy Emulsification
T. Joseph Lin
5. Surfactant Analysis in Cosmetic Preparations
Donald E. Deem
6. Interaction of Surfactants with Epidermal Tissues:
Biochemical and Toxicological Aspects
Edward J. Singer and Eugene P. Pittz
7. Interaction of Surfactants with Epidermal Tissues:
Eugene R. Cooper and Bret Berner
8. Surfactants and the Preservation of Cosmetic Preparations
Karl Heinz Wallhäusser
9. Surfactants in Shampoos
10. Surfactants in Oral Hygiene Products
11. Surfactants for Skin Cleansers
12. The Role of Surfactants in Aerosols
13. Surfactants in Cosmetic Suspensions
14. Index to Surfactant Structures and CTFA Nomenclature
Martin M. Rieger
William Abraham Research and Development, CYGNUS, Inc., Redwood City, California
M. P. Aronson Personal Washing Research, Unilever Research Laboratory Port Sunlight,
Merseyside, United Kingdom
John C. Brahms Research and Development, Colgate-Palmolive Company, Piscataway,
Robert H. Cagan Research and Development, Colgate-Palmolive Company, Piscataway,
Francesc Comelles Surfactant Technology, Centro de Investigación y Desarrollo,
Donald L. Courtney, Sr. Emulsions REZ, Landenberg, Pennsylvania
Jane M. Eldridge Analytical Services, Rhône-Poulenc, Inc., Cranbury, New Jersey
George E. Fischler Analytical Sciences/Microbiology, Colgate-Palmolive Company,
Piscataway, New Jersey
Thomas Förster Chemical Research, Henkel KGaA, Düsseldorf, Germany
Stig E. Friberg Department of Chemistry, Clarkson University, Potsdam, New York
Alan P. Greene Personal Washing Product Development, Lever Brothers Company,
Edgewater, New Jersey
J. L. Grossiord Physique Pharmaceutique, Université de Paris-Sud, Châtenay-Malabry,
Gary L. Grove KGL's Skin Study Center, Broomall, Pennsylvania
Genji Imokawa Biological Science Laboratories, Kao Corporation, Haga, Tochigi, Japan
David W. Ingersoll Consumer and Marketing Research, Givaudan-Roure, Teaneck, New
H. E. Junginger Department of Pharmaceutical Technology, Leiden/Amsterdam Center for
Drug Research, Leiden, The Netherlands
John N. Labows Research and Development, Colgate-Palmolive Company, Piscataway,
Daniel D. Lasic Consultant, Drug and Gene Delivery Consultations, Newark, California
Belinda Lee Skin Research, Colgate-Palmolive Company, Piscataway, New Jersey
Mark Leonard COSPHA, Henkel Organics, Belvedere, Kent, England
Boyce M. Morrison, Jr. Skin Clinical Investigations, Colgate-Palmolive Company,
Piscataway, New Jersey
Richard I. Murahata Clinical and Appraisal Science, Unilever Research U.S., Edgewater,
Drew Myers Consultant, Rio Tercero, Córdoba, Argentina
Donald S. Orth Research and Development, Neutrogena Corporation, Los Angeles,
Morton Pader* Consumer Products Development Resources, Inc., Teaneck, New Jersey
Francis Puisieux Physico-Chimie-Pharmacotechnie-Biopharmacie, Université de Paris-Sud,
Charles Reich Advanced Technology/Hair Care, Colgate-Palmolive Company, Piscataway,
Linda D. Rhein World Wide Therapeutic Skin Care, Johnson & Johnson Consumer
Products, Skillman, New Jersey
Martin M. Rieger Consultant, M & A Rieger Associates, Morris Plains, New Jersey
Perveen Y. Rizvi Skin Clinical Investigations, Colgate-Palmolive Company, Piscataway,
Diana D. Scala Skin Clinical Investigations, Colgate-Palmolive Company, Piscataway, New
Monique Seiller Physico-Chimie-Pharmacotechnie-Biopharmacie, Université de Paris-Sud,
Paul T. Sharko Personal Washing Product Development, Lever Brothers Company,
Edgewater, New Jersey
F. Anthony Simion Research and Development, The Andrew Jergens Company, Cincinnati,
Walter Sterzel Department of Toxicology, Henkel KGaA, Düsseldorf, Germany
Holger Tesmann CFTCOSPHA, Henkel KGaA, Düsseldorf, Germany
Paul Thau Technology Surveillance, Cosmair, Inc., Clark, New Jersey
Carles Trullás Research Department, Laboratories Isdin, Barcelona, Spain
Christopher D. Vaughan SPF Consulting Labs, Inc., Ft. Lauderdale, Florida
Armin Wadle Product Development Skin CareCOSPHA, Henkel KGaA, Düsseldorf, Germany
Jiang Yang Surfactants and Specialties North America, Rhône-Poulenc, Inc., Cranbury,
Joel L. Zatz Department of Pharmaceutics, Rutgers University College of Pharmacy,
Piscataway, New Jersey
Surfactant Chemistry and Classification
Martin M. Rieger
Consultant, M & A Rieger Associates, Morris Plains, New Jersey
I. Introductory Comments 1
A. Definitions and Structural Requirements 1
B. Utility and Selection of Surfactants in Cosmetics 2
C. Classification 3
D. Nomenclature 3
II. Group Description 4
A. Amphoterics 4
B. Anionics 6
C. Cationics 15
D. Nonionics 19
Definitions and Structural Requirements
The term surfactant is shorthand for the more cumbersome "surface active agent."
Surfactants as a group have the ability to modify the interface between various phases.
Their effects on the interface are the result of their ability to orient themselves in
accordance with the polarities of the two opposing phases. Thus the polar (hydrophilic)
part of the surfactant molecule can be expected to be oriented toward the more polar
(hydrophilic) phase at a given interfacial contact site. Similarly, the nonpolar (lipophilic)
portion of the surfactant molecule should contact the nonpolar (lipophilic) phase. Each
surfactant molecule has a tendency to reach across (bridge) the two phases, and such
substances have, therefore, also been called amphiphilic.
One of the prerequisites for an amphiphilic molecule is possession of at least one polar
and at least one essentially nonpolar portion. The orientation of a 1,2-dodecanediol
molecule at a mineral-oil/water interface is readily predictable from the preceding
discussion, but the positioning of 1,12-dodecanediol at a similar interface is not as
obvious; it would be expected to be different and more complex than that of the 1,2-
isomer. Despite their chemical similarity, the surfactant activities of these two compounds
can be expected to be different. It is apparent from this that a surfactant's behavior or
utility, e.g., as an emulsion stabilizer, is unrelated to its empirical formula. Instead, a
surfactant's spatial configuration, i.e., the molecule's structure, plays a critical role in
determining its application in cosmetics.
Utility and Selection of Surfactants in Cosmetics
Those who require and use surfactants tend to define surfactants on the basis of
performance. Regardless of diverse theoretical considerations, practicing cosmetic
formulators have developed a usage classification that they find practical in their day-to-
day activities. As a rule, a surfactant is soluble in at least one of the contacting phases
and is used to perform one or more of the following tasks:
Surfactants are useful for creating a wide variety of dispersed systems, such as
suspensions and emulsions. They cleanse and solubilize and are required not only during
manufacture but are also essential for maintaining an acceptable level of physical
stability of thermodynamically unstable systems, such as emulsions. Few modern
cosmetic products exist that do not depend on one or more surfactants to create and
maintain their desired characteristics.
It is the practitioner's responsibility to select one or more surfactants that can perform
the task at hand. As a result of prior experience, formulators usually can identify those
surfactant structures that can be expected to be most useful for achieving the desired
The cosmetic formulator's choice of surfactants is more limited than that of the industrial
chemist. Some of the criteria influencing selection are briefly noted below:
SafetyAdverse reactions to any surfactant used in a finished cosmetic must be minimized.
Odor and ColorOdoriferous or deeply colored surfactants can affect the esthetics of a
finished product and should be avoided.
PurityImpurities present in some surfactants may make the surfactant unacceptable for
Despite these and other limitations and the obvious requirement of cost, the cosmetic
chemist must make a selection from about 2000 different commercially available
The selection for the specific formulation task requires insight into the general
chemical characteristics of surfactants (this chapter) and an understanding of the
physichochemical behavior of these amphiphiles (Chapter 2).
Classification or categorization of the thousands of different surfactants on the basis of
generally recognized principles is clearly desirable. Thus it would appear practical to base
such a scheme on the surfactant's functionality. Creating groupings based on such
functional groups could in all likelihood be made without regard to commonly accepted
chemical or physical characteristics. A typical functional scheme was developed in the
CTFA (Cosmetic Ingredient Handbook)  by creating six functional categories for
Surfactants, Cleansing Agents
Surfactants, Emulsifying Agents
Surfactants, Foam Boosters
Surfactants, Solubilizing Agents
Surfactants, Suspending Agents
An entirely different means for classification might be based on the nature of the
hydrophobic portions of surfactants. Such a classification would create groups based on
the presence of hydrophobes derived from paraffinic, olefinic, aromatic, cycloaliphatic, or
heterocyclic hydrophobes. This type of classification could be of particular interest to
specialists who may wish to compare substances on the basis of physiological effects
related to the origin of the lipophilic constituents.
The most useful and widely accepted classification is based on the nature of the
hydrophilic segment of the surfactant molecules. This classification system has universal
acceptance and has been found to be practical throughout the surfactant industry. This
approach creates four large groups of chemicals: amphoterics, anionics, cationics, and
nonionics. This system categorizes surfactants on the basis of their ionic or nonionic
character, does not consider differences in the hydrophobic (nonpolar) segment, and
It is common practice to depict surfactant molecules as ball and stick figures:
In this cartoon, the hydrophobe is represented by a stick; the ball represents the
hydrophilic grouping, which may carry a positive and/or a negative charge or no charge; X
represents the counter ion required for electroneutrality of the molecule.
The nomenclature of surfactants can become very complex and confusing. For the
purpose of labeling of cosmetics in accordance with U.S. regulation, the Cosmetics,
Toiletry and Fragrance Association has created names for cosmetic ingredients. It is likely
that these names will soon be accepted in many other countries in the hope that a
worldwide agreement on this INCI* nomenclature can be reached between governmental
regulatory agencies and the trade associations concerned with cosmetics.
Rules for creating these names are included in the International Cosmetic Ingredient
Dictionary . The names are intended to be descriptive for laypersons as well as the
more technically oriented. The assigned names are not as precise as the names assigned
by Chemical Abstracts and eliminate the need for using proprietary trade names. The
INCI names are used in this chapter wherever possible.
Some abbreviations used in the text are identified below:
Surfactants are classified as amphoteric ifand only ifthe charge(s) on the hydrophilic head
change as a function of pH. Such surfactants must carry a positive charge at low pH and a
negative charge at high pH and may form internally neutralized ionic species (zwitterions)
at an intermediate pH. These features of amphoterics are illustrated below with the
behavior of lauraminopropionic acid at various pH levels:
Low pH: The surfactant molecule is a cation.
Intermediate pH: The surfactant molecule is a zwitterion.
High pH: The surfactant molecule is an anion.
In this example, R represents the lauryl alkyl group, while X and C+ are the required
counter ions. The behavior of this substance must be compared with that of lauryl
Low pH: The surfactant molecule is a cation.
Intermediate pH: The surfactant molecule may be a zwitterion.
*INCI = International Nomenclature Cosmetic Ingredient
Lauryl betaine contains a quaternary nitrogen atom regardless of pH. The ionization of
the carboxylic acid group is, however, pH dependent, and internal compensation is
possible. Lauryl betaine is properly classified as a quaternary surfactant. In cosmetic
usage, betaines and related molecules exhibit some functions associated with
amphoterics. Although some authorities have at times classified betaines as amphoterics,
they are classified here as quaternaries.
The hydrophilic groups in amphoterics commonly are primary, secondary, or tertiary
amino groups and an ionizable acidic group, i.e., COO, , or rarely on the same
molecule. Two types of amphoterics exist:
A 1. Alkylamido Alkyl Amines
A 2. Alkyl Substituted Amino Acids
Alkylamido Alkyl Amines
These substances are synthesized by acylation of the primary amino group of aminoethyl
ethanolamines (NH2CH2CH2NHCH2CH2OH) with a long chain (fatty) acid derivative. The
resulting cyclic 2-alkyl hydroxyethyl imidazoline is hydrolyzed in the subsequent alkylation
step with chloroacetic acid or ethylacrylate to yield a complex mixture of mono- or
dicarboxy alkyl derivatives:
Alkylation with, for example, hydroxypropylsulfonic acid, yields a more complex tertiary
amine. Commercial products are mixtures containing soaps and the hydrolysis product of
the alkylating agent. They are sold as salts (usually sodium) or as free acids. At or near
neutral pH they may exist in zwitterionic form. The amide linkage in these molecules may
be subject to hydrolysis, but no report of chemical instability in cosmetics has been
Alkylamido alkyl amines are generally water soluble and are compatible with most other
cosmetically useful surfactants. They reportedly reduce the tendency of anionics to elicit
eye irritation without significantly interfering with their foaming characteristics.
These amphoterics exhibit substantivity to hair and skin proteins and act as conditioning
and antistatic agents. Their primary use is in shampoos and miscellaneous skin cleansers.
They are, however, not widely used as detersive surfactants (cleansing agents) and are
not effective emulsifying agents.
Alkyl Substituted Amino Acids
Alkyl substituted amino acids are prepared by alkylation of various synthetic and natural
amino acids or by the addition of an amine to an a, b unsaturated alkanoic acid. Some
typical structures follow:
As a group, these compounds exhibit excellent stability under conditions of cosmetic use.
Alkyl substituted amino acids foam copiously, especially above their isoelectric point. At
low pH levels they behave as cationics and foam poorly. They can be used as emulsifiers.
As amphoterics, they are substantive to hair and find their most important uses in various
hair coloring and hair conditioning products.
All surfactants in which the hydrophilic head of the molecule carries a negative charge are
classified as anionics. The group of anionic surfactants includes types of great industrial
importance and substances widely used in cosmetics. As a rule, they are inactivated or
even form complex precipitates in the presence of cationic surfactants. This complexation
is generally attributed to salt formation in which the ionized species react in
stoichiometric proportions. The complexes may be solubilized in aqueous systems
containing large amounts of anionics.
For the sake of classification, anionic surfactants may be subdivided into five major
chemical classes and subgroups:
B. 1. Acylated Amino Acids and Acyl Peptides
B. 2. Carboxylic Acids (and Salts)
B. 2. (a) Alkanoic Acids
B. 2. (b) Ester-functional Carboxylic Acids
B. 2. (c) Ether-functional Carboxylic Acids
B. 3. Sulfonic Acid Derivatives
B. 3. (a) Taurates
B. 3. (b) Isethionates
B. 3. (c) Alkylaryl Sulfonates
B. 3. (d) Olefin Sulfonates
B. 3. (e) Sulfosuccinates
B. 3. (f) Miscellanous Sulfonates
B. 4. Sulfuric Acid Derivatives
B. 4. (a) Alkyl Sulfates
B. 4. (b) Alkyl Ether Sulfates
B. 5. Phosphoric Acid Derivatives
The members of these five classes form water soluble salts with alkali metals and low
molecular weight amines, especially alkanol amines.
The members of subgroups B.1 and B.2 above depend on ionization of the carboxylic acid
group for aqueous solubility. On the other hand, salts formed with alkaline earths or
heavy metals exhibit limited or no solubility in water.
Acylated Amino Acids and Acyl Peptides
These substances are usually prepared by the reaction of a natural amino acid or of a
peptide with a long-chain fatty acid derivative. In this reaction, primary amino groups are
converted into acylated amido groups. This destroys the zwitterionic character of the
amino acid or of the peptide and increases the acidity of the carboxylic acids. After
completion of the acylation, these acid groups are frequently neutralized with a suitable
alkali. The following examples illustrate some of the structures:
Collagen or some of its hydrolysis products are the most common sources of the protein.
The level of hydrolysis (enzymatic or chemical) is not generally specified, and so-called
acylated peptides are likely to contain considerable amounts of acylated amino acids.
Since some of the amino acids contain more than one site for acylation (e.g.,
hydroxyproline), the end products are probably rather complex mixtures and may include
some simple soaps.
The acyl sarcosinates (derived from N-methyl glycine) occupy a special niche in
cosmetics. These substances behave like soaps. The key to their performance and
mildness is the fact that the carboxyl group has a lower pKa than that of typical fatty
acids. The salts of the sarcosinates are water soluble and can be used at pH levels near
or even slightly below neutrality.
Acylated amino acids, depending on molecular weight and complexity, foam modestly
and are generally viewed as exceptionally mild. They find use in skin and hair cleansing
products and have been included in syndet bars. They reportedly exhibit substantivity to
hair and skin proteins. Members of this class are sometimes identified as amphoteric.
Under conditions of cosmetic usage (pH 4 to 9), acylated amino acids or peptides carry an
anionic charge that is neutralized by a suitable cation. Their reported substantivity to hair
or skin is the result of some unidentified proteinprotein interaction unrelated to the
charge on the surfactant's head group.
Acylated amino acids are amides and subject to chemical (or enzymatic) hydrolysis.
They are, however, stable at the pH commonly found in cosmetics but are subject to
microbial attack. Preservation against spoilage remains a major problem, especially in the
case of the peptide-derived products.
Carboxylic Acids (and Salts)
B. 2. (a)
The most important members of this subgroup are the fatty acids derived from plant and
animal glycerides. These natural acids normally possess an even number of carbon atoms
and carry only one carboxylic acid group. The unsaturation in natural fatty acid is almost
exclusively cis. A few natural fatty acids also contain a hydroxy group. In addition, some
alkanoic acids are prepared synthetically, especially those in which the alkyl group is
Fatty acids are obtained by the alkaline hydrolysis of fats and oils. Acidification after
removal of unsaponifiables yields a water insoluble fatty acid blend named on the basis of
its source, e.g., olive oil fatty acids. Specific fatty acids (e.g., oleic acid), can be isolated
from these mixtures by various chemical and physical techniques.
Alkanoic acids, as a group, are important industrial chemicals and are used in the
synthesis of many types of substances. One of the most important modifications of
alkanoic acids is reduction to fatty alcohols, which are then processed further to yield a
variety of surfactants. Free alkanoic acids are of limited use in cosmetics, but the water
soluble salts (soaps) are amongst the most useful surfactants known. Soaps have been
utilized as cleansers and detersive agents since antiquity. In modern practice, soaps are
the alkali or low molecular weight amine salts of alkanoic acids. Their water solubility
depends on the pH of the system and on the cation. As a rule, potassium salts are more
soluble than the sodium salts. The alkanoic acids are weak acids, with a reported pKa of
about 56. Therefore soapsas salts of weak acidsyield alkaline aqueous solutions due to
their dissociation in water.
The solubility of alkali or amine salts of alkanoic acids in water decreases as the length of
the alkyl chain increases. Thus, sodium stearate, especially in the presence of some free
stearic acid, is insoluble enough to permit manufacture into soap bars. The alkaline earth
and metal salts of alkanoic acids are water insoluble. Thus, calcium salts precipitate in
aqueous systems leading to the formation of so-called soap scum.
Alkanoic acid salts in which the alkyl chain contains about ten or fewer cations are not
useful as surfactants, i.e., they do not foam well, have no detersive qualities, and are
poor emulsifiers. The stearic acid of commerce contains about 45% of octadecanoic and
55% of hexadecanoic acids. The product may include small amounts of oleic acid and
other acids normally found in the starting lipid. Modern grades of stearic acid are
primarily prepared by hydrogenation of soybean fatty acids. For illustrative purpose, the
following structures are included:
Water soluble soaps are used as skin and hair cleansing agents, while the insoluble
derivatives (e.g., zinc laurate or magnesium stearate) are used for lubricating solids to
improve flow properties, act as binders, and increase the viscosity of nonaqueous
systems. Sodium stearate is soluble in warm ethanol and tends to gel upon cooling. Thus
this substance has found extensive use in the formulation of alcohol-based stick
Water soluble and water insoluble soaps are good emulsifiers, the former primarily for
o/w emulsions, while soaps such as aluminum stearate tend to form w/o emulsions. As a
rule, oleic acid salts are especially useful emulsifiers, but their usage is restricted by the
tendency of this unsaturated acid to form malodorous or discolored peroxidation products.
One of the most important applications of soaps is represented by shaving soaps in
general. Regardless of the method of shaving (brush, brushless, or aerosol), soap stocks
from various sources are commonly blended to provide the shaver with copious and
rapidly generated foam that lasts until shaving is completed.
The topical use of soaps for skin cleansing is considered safe, although it has been shown
that soaps can elicit adverse reactions on skin during closed patch testing .
B. 2. (b)
Ester-functional Carboxylic Acids
One type of ester-functional carboxylic acid is the small group of esters derived from
polycarboxylic acids in which at least one of the carboxylate groups is free to form a salt.
A typical example is stearyl citrate, the monoester of stearyl alcohol with citric acid.
An entirely different type is represented by the acylation compounds of lactyl lactate. In
their synthesis, two molecules of lactic acid are believed to react with each other, and the
dimer then reacts with a fatty acid. The structure of a typical emulsifier created by this
reaction is shown below:
Compounds belonging to this class are safe for use in foods (baked goods), are
occasionally used as cosmetic emulsifiers, and are reported to condition hair and skin.
B. 2. (c)
Ether-functional Carboxylic Acids
Compounds belonging to the group of ether-functional carboxylic acids have recently
gained some prominence in cosmetic usage. They may be viewed as alkylethers of
polyethyleneglycol in which the terminal OH group has been oxidized to a carboxy group.
The principal synthetic route depends on the alkylation (e.g., with chloroacetic acid) of an
ethoxylated alcohol (D.3.a). As derivatives of glycolic acid, their pKa is quite low. The
presence of the polymeric ether group increases the water solubility of these substances
even if the starting alcoholic hydrophobe is relatively bulky. A typical structure is provided
below for illustrative purposes:
The water solubility of the free acids increases with increasing levels of ethoxylation. In
this form, these compounds are useful as emulsifiers. Neutralization (usually with sodium
ion) yields surfactants with detersive and solubilizing properties. These compounds are
stable under normal conditions of cosmetic use. Compounds of this type have been shown
to reduce the skin irritation potential of other anionic surfactants [4,5] and are generally
milder themselves .
Sulfonic Acid Derivatives
The extremely stable CS bonds of these alkyl sulfonic acids distinguish them from
compounds containing hydrolyzable COS bonds. The oxidative state of the sulfur atom
also precludes most elimination reactions. Organic sulfonic acids are strong acids and in
cosmetics are used only as salts. The sulfonates are generally divided into six subgroups.
All sulfonates are chemically stable in cosmetics, and most are well tolerated on the skin.
B. 3. (a)
The taurates are a small group of compounds which are derived from taurine or N-methyl
taurine by acylation. In aqueous solutions these amides are not stable and are subject to
self-hydrolysis. Oh the other hand, they are stable in neutralized (generally sodium salt)
form. A typical structure of a taurate follows:
Taurates as a group foam well and have found usage in bubble baths and cosmetic skin
and hair cleansing products.
B. 3. (b)
Isethionates are the esters formed between isethionic acid (HOCH2CH2SO3H) and long-
chain alkanoic acids. Like the taurates, the isethionic acid esters are strong acids and are
subject to self-hydrolysis in aqueous systems. They are, therefore, useful in cosmetics
primarily as sodium salts, as shown below:
Isethionates are compatible with other anionic and nonionic surfactants.
The limited number of cosmetically useful isethionates does not reflect their importance
in liquid and solid skin cleansing products. Their irritation potential is considered to be
very low, and they are important constituents of syndet bars.
B. 3. (c)
Alkylaryl sulfonates are prepared by sulfonation of a number of alkyl substituted aromatic
hydrocarbons. The starting hydrocarbon may be obtained by alkylation of benzene,
naphthalene, toluene, or similar aromatic compounds. The alkyl s