Creative Developments (Cosmetics) Limited
Formulators;
it is time to widen your horizons
Paper given
before the Society of Cosmetic Scientists, Chepstow, 2000
Copyright John Woodruff
“…. it would seem that practically everything
has been done by now to perfect the technique of permanent waving. Little
remains to be known………. employing new chemicals may perhaps be a possibility,
but the chemist, as yet, has not taken a deep interest…..” “…X-ray treatment may be used to break
down the structure of the hair and reform it and it is obvious that professional
scientists rather than chemists and hairdressers will be responsible for any
future developments”. Quotation by a Professor Astbury from a book published in
1947 on hair.
Abstract
In 1941 De Navarre in The Chemistry and Manufacture of
Cosmetics, referred to the use of triethanolamine alkyl sulfates in shampoos
and in the 2nd Edition published in 1962 formulations using
ethoxylated lauryl sulfates in shampoos and bubble baths were described. In
1983 Hunting surveyed 483 shampoos on sale in the USA and listed ingredients by
the % of products in which they were found. Alkyl sulfates and cocamide DEA
headed the list and ethoxylated alkyl sulfates were the second most popular of
the primary surfactants. In 2001 Woodruff surveyed the current market and
realised that not only were there few differences in their composition but
almost all could have been made with ingredients available in 1983 and most
with those of 1962. Similar comments can be made about conditioning and styling
products.
The following paper is a reminder to formulating
chemists that there are many more ingredients available than sodium laureth
sulfate and cocamidopropyl betaine and that illustrating a label with a pretty
flower does not count as product improvement.
Keywords
Shampoo, Formulation, Surfactants, Condition,
Rheology, Foam, Cleansing, Anionic Surfactant, Amphoteric Surfactants,
Introduction
In 1941 De Navarre1 described new shampoos
using either monoethanolamine or triethanolamine alkyl sulfates. A 1954
handbook2 of cosmetic ingredients lists sodium lauryl sulfate and
volume 1 of De Navarre’s 2nd edition published in 19623,
gives a formula using sodium lauryl sulfate with triethanolamine lauryl
sulfate. In volume 2 are found the first references to the use of ethoxylated
lauryl sulfates in shampoos and bubble baths. De Navarre also describes the use
of electrolytes to thicken these products and warns of the irritating and
drying effects of the alkyl sulfates. For conditioning rinses cetrimonium
chloride, lauralkonium chloride and stearalkonium chloride were recommended and
ways of making 2-in-1 conditioning shampoos using mixtures of cationic and
anionic surfactants were discussed. Sarcosinates, taurates, betaines and
polypeptide derivatives were all mentioned.
In 1983 Tony Hunting surveyed the ingredient listing
of 483 shampoos on sale in the USA4. He listed ingredients by the %
of products in which they were found and gave them a rank order and a Relative
Importance Factor (RIF) that was calculated with reference to its position on
the ingredient listing.
|
Material |
% Shampoos |
Rank Order |
RIF |
|
Ammonium Lauryl Sulfate |
27.2% |
9 |
1 |
|
Lauramide DEA |
42.2% |
2 |
2 |
|
TEA-Lauryl Sulfate |
22.4% |
11 |
3 |
|
Sodium Lauryl Sulfate |
24.4% |
10 |
4 |
|
Cocamide DEA |
30.4% |
6 |
5 |
|
Sodium Laureth Sulfate |
20.1% |
13 |
6 |
|
Hydrolysed Collagen |
37.9% |
3 |
7 |
|
Formaldehyde |
29.7% |
7 |
15 |
|
Cocamidopropyl Betaine |
8.7% |
31 |
16 |
|
Cocamide MEA |
7.3% |
32 |
23 |
|
Ammonium Laureth Sulfate |
3.9% |
56 |
25 |
|
Panthenol |
10.7% |
24 |
30 |
|
Guar Hydroxypropyltrimonium Chloride |
2.3% |
206 |
265 |
|
Lauryl Betaine |
0.2% |
307 |
286 |
If similar ingredients are combined we get the
following distribution.
|
Lauramide DEA / Cocamide DEA / Cocamide MEA |
79.9% |
|
Ammonium Lauryl Sulfate/ Sodium Lauryl Sulfate/
TEA-Lauryl Sulfate |
74.0% |
|
Hydrolysed Collagen |
37.9% |
|
Formaldehyde |
29.7% |
|
Sodium Laureth Sulfate/ Ammonium Laureth Sulfate |
24.0% |
|
Panthenol |
10.7% |
|
Cocamidopropyl Betaine/ Lauryl Betaine |
8.9% |
|
Guar Hydroxypropyltrimonium Chloride |
2.3% |
So, nearly fifty years after De Navarre and
twenty-eight after the survey by Hunting, what has changed? The following is a survey
of a random selection of non-medicated shampoos available for less than £3.00
per bottle plus three designer shampoos added for variety. Not quite on the
same scale as Hunting but it includes many well-known names. The ingredients
were listed as follows: -
|
Material |
*/14 |
Material |
*/14 |
|
Sodium Laureth Sulfate |
13 |
Sodium Lauryl Sulfate |
1 |
|
Cocamidopropyl Betaine |
9 |
Cocamide MEA |
1 |
|
Pearl/Opacifier |
9 |
Ammonium Laureth Sulfate |
1 |
|
Panthenol |
5 |
Sodium Laureth Sulfosuccinate |
1 |
|
Cocamide DEA |
5 |
Ammonium lauryl sulfate |
1 |
|
Silicone Compound |
3 |
Lauryl Betaine |
1 |
|
Hydrolysed Collagen |
2 |
Decyl Glucoside |
1 |
|
Guar Hydroxypropyltrimonium Cl. |
2 |
Formaldehyde |
0 |
|
Lauramide DEA |
1 |
TEA-Lauryl sulfate |
0 |
Sodium laureth sulfate has replaced the alkyl sulfates
at the top of the list but this is partially a regional difference.
Cocamidopropyl betaine has significantly replaced cocamide DEA. Panthenol has increased
slightly in popularity and silicone compounds make their first appearance in
shampoos. Of course most of the samples make lyrical claims about the natural
extracts they contain but as these appear buried among the preservatives on the
ingredient listing it is hard to take them seriously. Obvious is the total
dominance of sodium laureth sulfate as the prime surfactant and of
cocamidopropyl betaine as the secondary one. Sodium chloride appeared in the
top five ingredients in almost all cases, in the top three in some. In the
International Cosmetic Ingredient Dictionary there are more than 180 anionic
surfactants plus 83 amphoteric and rather a lot of non-ionic ones. They may not
all be suitable for shampoo formulation but there is obviously a huge number
from which to choose. Sodium chloride is an excellent thickener for surfactant
systems but is it good for hair? Surely we as chemists can try and build a
little diversity into one of the most commonly used of all cosmetic products.
Shampoo; the
Essential Attributes
There are six essential attributes to a shampoo: cleansing, foam, condition, viscosity and aesthetic appeal combined with safety and mildness in use.
Cleansing is a function of the primary surfactant. To be an effective cleansing agent the surfactant system must work quickly at a relatively low temperature. It must be effective in hard and soft water, be able to remove lipids and other soils and residues left after previous hair treatments and it must not leave any residues of its own. It must be non-toxic and reasonably non-irritant to skin and eyes. It must be affordable!
It is these requirements that have made ammonium lauryl sulfate (ALS) and sodium laureth sulfate (SLES) the dominant primary surfactants for so long but besides alkyl and alkyl ether sulfates there are sarcosinates, isethionates, taurates, sulphosuccinates and olefin sulfonates; are they worth consideration?
The mechanisms of hair cleansing are complex. Undamaged hair has a hydrophobic surface to which lipids are strongly adsorbed. When hair is shampooed anionic surfactants are adsorbed to hair by their hydrophobic tails and the negatively charged heads orientate outwards. The fibre surface is thus wetted and non-polar materials are displaced. Semi-polar materials are solubilised into micelle structures and are removed by rinsing. Particulate matter adheres to hair through ionic and van de Waals forces, which are much reduced by the surfactant system and it is readily removed by rinsing.
When comparing surfactant systems the different mechanisms involved in cleansing should be considered; they are mostly favoured by anionic surfactants but non-ionic ones have an important part to play in solubilisation processes. The solubilisation process depends on the critical micelle concentration (CMC) and the number of micelles that aggregate together. Large micelles make large aggregates, which make it easier to absorb lipids within the micelle. Non-ionic surfactants and electrolytes pack themselves between the micelles of anionic surfactants, which increases the size of the aggregate and improves the solubilising of lipids. Thus ALS has a lower CMC and a higher aggregate number than SLS and is therefore a more effective cleanser. Ether sulfates have larger micelles and more are involved in micelle formation so they are more effective than non-ethoxylated alkyl sulfates.
Foam is also a function of the primary surfactant and few materials can compete with ALS or SLES for quick flash foam. Additional materials may depress the foam or make it creamier and stabilise it. Dialkanolamides were the firm favourite for three decades but are increasingly being replaced by amphoteric surfactants.
Conditioning: the common theme linking the majority of new materials for hair care is improved conditioning. Shampoos have changed from strong cleansers to be used weekly to mild formulations for daily use. Some manufacturers have simply reduced the active levels, others have increased the amphoteric content and many have included conditioning aids.
Viscosity is an important aspect of shampoo formulation. Products must have sufficient viscosity to stay on the palm of the hand prior to application but must not come out of the bottle as a globular lump. Anionic systems may be thickened by the addition of electrolytes or non-ionic compounds or by betaines. Sodium chloride and cocamidopropyl betaine (CAPB) are the materials of common choice but others are worth consideration.
Aesthetic appeal is difficult to quantify but colour, odour and pretty pictures on the label all play a part in consumer appeal.
Safety & mildness are essential attributes of a product that may be used every day and which can come into contact with skin and eyes. Alkyl sulfates and alkyl ether sulfates are aggressive surfactants that can irritate eyes and scalp and cause skin dryness. The effects are usually modified by the addition of amphoteric or non-ionic materials.
The Primary Surfactants
Alkyl sulfates and alkyl ether sulfates; exemplified by ammonium lauryl sulfate (ALS) and sodium laureth sulfate (SLES). These materials are relatively inexpensive, are virtually colourless and odourless, have good cleansing properties, give good flash foam and form products that are readily thickened. The foam however is relatively loose and unstable, ALS is an irritant and SLES leaves the hair feeling dry and with flyaway. There has been poor publicity about these ingredients on the web and in the literature circulated by certain pressure groups.
Acyl lactylates are a group of anionic surfactants that appear to have excellent foaming and cleansing properties. Their properties are largely determined by the carbon chain length of their fatty moiety as well as the cation used in their neutralisation (i.e., C8-C12 lactylates are good foaming agents; C10-14 lactylates are good foam boosters). Sodium caproyl lactylate is said to be an excellent foam booster and stabiliser when used in conjunction with CAPB or alkyl polyglycosides5.
Isethionates are the esters formed between isethionic acid and long-chain alkanoic acids and used as the sodium salt, sodium lauroyl isethionate. It is compatible with other anionic surfactants and is claimed to have a very low irritation potential. Their most common use is in syndet bars and liquid skin cleansers.
Olefin sulfonates are said to foam as readily as SLES, work well in hard water and are stable at a lower pH. It is easy to build viscosity into the system, they are competitive in price but are said to leave the hair feeling harsh.
Sarcosinates are most commonly represented by sodium lauroyl sarcosinate, the sodium salt of lauroyl sarcosine. It is said to foam well, have good cleaning properties and be mild to use. It is stable at acid pH, reduces static charge and imparts a light conditioning effect to the hair. It is suitable as the primary surfactant in baby and children’s shampoos but is more generally added as a secondary surfactant to SLES to reduce irritation. Sodium lauroyl sarcosinate is compatible with a wide range of cationic surfactants and germicidal antidandruff agents. Lipids do not affect its foaming properties so it is suitable for greasy hair and antidandruff products.
Sodium lauryl sulfoacetate is an excellent foaming, wetting, emulsifying and cleansing surfactant with good stability in hard water. Key performance characteristics include excellent foam stability, hard water stability, good viscosity building and mildness6. Although suitable as a primary surfactant it is generally used as an additive to SLES systems, resulting in improved foaming and cleansing with lower irritation potential than SLES alone.
Taurates are the stable salts of N-methyl taurine. They foam well and at one time were used quite extensively in foam baths and hair shampoos. Taurates are known to possess excellent wetting, foaming, detergent and dispersing properties, and have a conditioning effect on hair. They are recommended for antidandruff shampoos and are said to reduce dandruff formation and damage to hair cuticle because of their lower irritation potential. Taurates are hard water tolerant and stable over a wide pH range.
Although some of the materials above are of interest there
was little evidence of the majority of these appearing in common brands of
shampoos. It does not look as if alkyl sulfates and alkyl ether sulfates have
any serious competition as the primary surfactants in cost conscious products.
However many of the above materials are suitable as secondary additives and
other materials have been introduced to work in synergy with them, particularly
the alkyl polyglycosides.
The
Secondary Surfactants
Many of the surfactants appearing above are perhaps better described as secondary, if only because cost precludes their use as the main surfactant. Secondary surfactants are usually non-ionic like the alkanolamides and alkyl polyglycosides or amphoteric like the betaines. Before a purist points out that betaines are not truly amphoteric (they have a negative charge at acid pH but are non-ionic at alkaline) I will admit that I have labelled all zwitterionic compounds as amphoteric, it makes for simplicity.
Amphoteric compounds are usually thought to be milder than anionic surfactants and are often used in combination to reduce the irritation potential of the latter by reducing the CMC. A useful side effect of adding an amphoteric surfactant to a cosmetic product is the bacteriastatic effect shown by many of them. Less than 75ppm of lauryl betaine is said to be effective against Aspergillus niger, Staphylococcus aureus and Listeria monocytes. It is less effective against Pseudomonas aeroginosa, requiring 75,000ppm. but it is a means of reducing preservative levels in surfactant products while improving foam volume and adding a conditioning effect.
Alkanolamides; e.g. cocamide DEA, lauramide DEA, For thirty years these were unassailable as the most common secondary surfactants to be used with alkyl sulfates and alkyl ether sulfates. They improve foam heights and foam stability; they are excellent solubilising agents; they assist in viscosity build and they are relatively inexpensive. Then betaines started to encroach on this popularity and the nitrosamine problem further reduced their use, although they still appear in approximately 30% of all shampoos. The monoethanolamides, lauramide MEA and cocamide MEA are also used.
Alkyl betaines are the primary secondary surfactant of choice today. Lauryl betaine was the first to be used in a significant number of formulations but cocamidopropyl betaine (CAPB) is now the clear leader in popularity. An alternative material is capryl/capramidopropyl betaine that is said to be exceptionally mild. Betaines in general and CAPB in particular are good foam boosting and stabilising agents and contribute towards building viscosity although this is also a function of their high salt content.
Alkyl polyglycosides (APGs) only became available in commercial quantities in the last decade and have since changed their trade names and their INCI designations and are more properly termed alkyl glucosides. Although initially launched as possible substitutes for alky ether sulfates, alkyl glucosides have mainly found application in association with them. Being naturally sourced and biodegradable, APGs have a number of advantages and they foam well, are good foam boosters and stabilisers and are particularly mild in action.
Amine oxides e.g. lauramine oxide and dihydroxyethyl cocamine oxide, are mildly cationic under acidic conditions but this is now believed to be because of contamination by un-reacted amine and they are probably non-ionic. They are used to build viscosity and to improve foam qualities and may be used in hair colouring shampoos containing basic dyes.
Ethoxylated Alkanolamides e.g. PEG-6 cocamide and PEG-6 lauramide avoid the possible nitrosamine problem and are excellent solubilising aids and improve foam quality and product viscosity.
Imidazoline derivatives include glycinate and amphoacetate compounds and have been known to the industry for several decades. They are extremely mild and can be used to reduce irritation of other surfactants. They have good foaming action and work well in combination with SLES. They are hard water tolerant and stable over a wide pH range but shampoo made with them can be difficult to thicken. Recent introductions include a number of vegetable-derived amphoglycinates of interest to formulators of natural products and a new group of alkylpolyamphopolycarboxyglycinates (APACs) including cocoamphopolycarboxyglycinate that have useful conditioning and foam stabilising properties.
Protein-based surfactants; e.g. Hydrolysed wheat protein olivate. This is a new material that is said to be competitive with SLES in foam and cleansing efficiency, but as with many possible substitutions its price precludes its use as a primary surfactant. Other surfactants in this group are derived from wheat and other vegetable proteins and from collagen. All are claimed to improve lather properties, to be mild in action and to improve the condition of the hair.
Sulfosuccinates are a wide group of chemicals exhibiting different application properties. Typical examples are dioctyl sodium sulfosuccinate and disodium lauramido MEA sulfosuccinate. They do not produce stable foams but are relatively mild and find application as secondary surfactants.
The above is not an exhaustive list but
does represent the main groups available to the shampoo formulator.
Conditioning and Body
There are many ways of improving hair condition. SLES and other anionic surfactants leave the hair feeling dry and difficult to manage. The introduction of a suitable secondary surfactant greatly reduces this and hair condition is much improved. Further improvements are possible using suitable additives.
Cationic polymers are used as conditioning additives. Used at 0.1% to 0.5% they form a complex within the shampoo that is soluble in the large excess of anionic surfactant present. On dilution by application to wet hair the polymer is precipitated and adsorbed onto the hair with sufficient attraction to resist being lost at the rinse stage.
When claiming conditioning activity in a shampoo proof
of efficacy should be considered. The following chart shows the main criteria
and methods of measurement.
|
Criteria |
Method |
|
Wet combing |
Combing force reduction |
|
Dry combing |
Combing force reduction |
|
Reduction in static charge |
Fly away effect |
|
Removal of conditioning aid |
Analysis |
|
Volume and body |
Sensorial assessment |
|
Creaminess of lather |
Sensorial assessment |
At the IFSCC 1998 Congress, Dr. Peter Hössel7 described comparative studies into the action of conditioning polymers. The investigations were carried out on formulations that contained sodium laureth sulfate / cocamidopropyl betaine and the cationic polymers, polyquaternium-7, polyquaternium-10, polyquaternium-44, and guar hydroxypropyltrimonium chloride. Wet combability and other characteristics were measured to demonstrate the efficacy of these conditioning polymers. Hössel found that only cationic polymers with a very high molecular weight were effective as conditioners in shampoos based on anionic surfactants. They do not need to have a high positive charge but molecular structure is important.
A branched polymer is more coiled than a linear polymer and therefore less hydrated in water-based formulations. The polymer/surfactant complex is more readily precipitated and deposited on the hair upon dilution of the shampoo and a coiled polymer is less strongly adsorbed on hair than a straight polymer and is therefore easier to desorb if necessary. Polyquaternium-10 and polyquaternium-44 were the only polymers whose residues could be desorbed from the hair by rinsing with water/surfactant. Polyquaternium-7 and the cationic guar gum could not be completely removed from the hair. This suggests that shampoo formulations containing these polymers tend to over condition the hair and to cause build-up.
Silicone compounds are popular conditioning additives for shampoos but it is important to select the correct silicone for the product; the cyclomethicones are volatile and may be added to shampoos to decrease drying time. Dimethicone copolyols are non-ionic surfactants that increase the wetting of hair while enhancing the foaming characteristics of shampoo and because of their solubility; they may be used in clear systems. Dimethicones are low surface tension liquids which form monolayer films over the hair shaft, imparting gloss, substantivity and soft feel. Amodimethicones have polar amine groups with a strong affinity for hair and they provide excellent dry and wet combing, along with softness, shine and static control.
Dimethiconols are high molecular weight silicone gums with excellent conditioning properties but need to be blended with a cyclomethicone or dimethicone to make them suitable for application and much care is needed to incorporate them into shampoo. The conditioning effect of silicone compounds in shampoos is dependent on high molecular weight and it is essential to