Introduction
Ingredients providing care for cosmetic cleansing applications for skin and hair
are becoming increasingly important. Ideally, if an optimum use is made of these
care ingredients in the formulations, the positive effects on skin and hair can
actively support the marketing promotion of the finished product. The application
engineer may ask: Which substance is the best for my product, and at what concentration?
The right balance is important to avoid an overload of care that negatively influences
cleansing and lathering.
In the following, two different test designs (on skin and hair, respectively)
are presented, featuring esters produced from vegetable raw materials as active
ingredients.
Function of esters
Esters or ingredients with functional ester groups constitute
structural elements that accompany us unnoticed in a variety of areas of our
daily life. They are involved in forming fragrances and flavors, e.g. wines,
brandies or whiskeys develop their full bouquet just by forming esters during
storage. Esters also have an essential significance in cosmetic formulas. By
virtue of their versatility, substances with functional ester groups provide
a wide range of possible applications in cosmetics.
In this article, esters used for surfactant preparations with
the most varied effects on skin and hair are described. In terms of applied
technology, the selected ingredients can be classified into two different applications,
i.e. for clear or turbid products. The following three substances shall illustrate
this:
Glyceryl Oleate (GMO) may be incorporated in surfactant-based
formulas at a concentration of up to 1.5 %, resulting in a clear product.
The other two substances, Cetyl Palmitate (CP) and Glycol
Distearate (EGDS), represent waxy materials which are only suitable for turbid
formulations.
Since cold-processability is an important requirement in the
cosmetics industry, all three ingredients were used preferably after introduction
into a cold processable compound. Examples of such compounds are Lamesoft PO
65, Lamesoft PW 45 and Lamesoft
TM Benz. An advantage of compounds is that the use of
wax dispersions is possible. They have closely defined particles of uniform
size.
The magnifications give us an idea of the character of particles, their
size and distribution. All pearlescent products with a particle mean size significantly
larger than 10 microns have a low effectivity. With decreasing particle size the
effects on skin and hair become more appreciable. An optimum wax dispersion has
a proportion of 50 % particles with approximately 1 micron.
Tests performed on the skin
Analyses of skin surface lipids show a large variety of different
substances, the largest proportion being waxes and fats, with ester functions
(1).
Previous research results have frequently revealed that
small amounts of GMO are found even in untreated skin. Since we had already developed
GMO as an effective lipid layer enhancing agent, this evidence was of special
interest for us. In other tests, four hours after completely removing the skin
lipids from the foreheads of test persons, the natural GMO content was tested.
The results showed that there is a natural GMO regeneration in all test persons.
In order to develop substances with a high performance, we
have to ensure that -- during application -- these substances are adsorbed into
the skin.
The adsorption behaviour was proven for GMO (clear formula)
and CP (turbid formula) by using various formulating concepts.
Depending on the concentration, the proportion of lipid
layer enhancing agent measured on the skin increases. In addition, tests covering
a prolonged application period show a correlation to the frequency of application.
Various methods have been used to extract the lipids and the active ingredients
on the skin surface and in the skin, respectively.
Various extraction methods as well as skin stripping show
that GMO penetrates into the stratum corneum. By contrast, CP remains on the
surface. We were able to demonstrate this with the aid of ultrasound imaging.
The investigations yielded in very impressive ultrasound images.
When treatment with surfactants reduces the signals (reflection)
from the upper layer of the skin, the use of CP leads to an integration of wax
particles into the upper skin layer of the stratum corneum. Comparable effects
can be found when using vaseline (2).
So far this report has focussed on the application properties of the selected
ingredients. The desired effects on the skin resulting from these applications
and corresponding skin-torsional measurements proving the positive effects will
follow in the next few paragraphs.
Any change in torsion allows us to draw conclusions regarding elasticity, smoothness
and -- indirectly -- on the moisture content of the skin. Our measurements showed
that the negative surfactant effect is significantly reduced by GMO, and also
by CP. Above a level of 1.5% CP, the condition of the skin was even improved
compared to its untreated condition (3).
Other changes in skin structure are monitored by the FOITS
method (Fast Optical in-vivo Topometry of Human Skin). The skin profile of 30
test persons was improved significantly by a GMO-containing formula applied
over a period of three weeks (4).
The degree of improvement in depth- and micro-roughness is
a measure of the softness and smoothness of the skin. The reduction in skin
surface area is also beneficial with regard to damaging environmental influences.
Results obtained 24 hours after the last application show that this is not just
a short-term effect (5).
The last and certainly the most important effect of our tested
substances is the positive influence on the skin moisture. However, since such
an effect is relatively small in rinse-off applications, a very sensitive method
had to be selected. The MRI method (magnetic resonance imaging) used enables
precise measurements of skin moisture, and provides reliable results in spite
of climatic influence. Similar to the preceding measurements, it is necessary
to have a prolonged treatment over a long period of time, and to effect pre-conditioning
of the skin at the beginning of the test. T2-measurements (transversal relaxation
time) reflect the changes in hydration (6).
To support the accurate interpretation of the results obtained,
isolated skin was used in pilot tests and correlated with the readings (7,8).
The test areas on the skin of the test persons were additionally tested with a
corneospinometer. This device tests skin elasticity in a manner comparable to
torsional measurements.
The two measurements confirmed the positive influence of GMO.
Readings after 24 hours showed an increase of 77% which further increased to
98% after 48h compared to the placebo treatment, with a significance of >
99%. The long-term effect was confirmed by the 48-hour value.
Sensory assessment was the last method used to prove the efficiency of an EGDS
wax dispersion. The two different concentrations clearly show the inter-dependencies
in a surfactant formula.
Addition of 1.1% EGDS, while having a positive effect on the lather also produces
a better skin texture in comparison to the placebo formula. An increase of the
EGDS proportion to 2.2% decreases the foam generation while improving the perceivable
care effect.
To sum up, positive evidence has been given to prove the effects on the skin,
both with a clear GMO formula and with fine-disperse wax dispersions of CP and
EGDS. Besides the lipid-layer enhancing of the skin (substantivity), additional
conclusions can be drawn as to improved elasticity, smoothness, softness and
skin moisture. Sensory assessment may prove that these are noticeable effects.
Hair studies
Effects on hair are usually easier to measure than effects
on skin. This is due to the large surface area of hair compared to skin. Therefore
it was not surprising that higher values are obtained from substantivity measurements.
A certain natural content of GMO is measurable in hair
as well, as already shown for skin.
To measure changes on the hair surface the AFM method (Atomic
Force Microscope) was used.
Besides visualizing the surface of hair strands, corresponding
changes can be measured as well with this method. The results show any changes
in surface quantity and microscopic surface roughness. The interpretation of
these results is as good as the representative quality of the areas tested.
To illustrate the effects of the active substances more clearly, the surfactant
effect (placebo) was subtracted from the GMO- and CP-results.
It is evident that both esters, GMO and CP, reduce the
surface area when frequently used over a prolonged period, thus counteracting
the effect of the surfactant.
Microscopic roughness is reduced in much the same way as the
condition of the hair is improved. The duration of treatment was 75 minutes
and is based on an assumed 15 applications of 5 minutes each, which we considered
to be practicable. The results obtained from the AFM method were then correlated
with the technical effects.
The absorption behavior of GMO and CP shows a decrease in
the force required for combing wet hair. A reduced roughness of the hair's surface
supports to a more smooth and softer appearance and leads to a conditioning
that facilitates gentle combing.
Measurements of hair gloss are very complicated due to various
influential factors. Gloss is the consequence of a decrease in scattered light,
which is found with rough hair with protruding cuticle edges. But also dirty
and dry hair is lustreless. That is why thorough cleaning is the first step
to improve gloss (9, 10).
The diagram clearly illustrates the placebo effect (cleaning).
The first treatment period produces a gloss level that cannot be improved by
any further treatment. The influence of GMO and CP can be clearly seen in the
illustration. The values are higher than those of the placebo with its pure
surfactant effect. Two other substances analyzed in this context (silicone oil
and cationic polymer) lead to a continuous increase in gloss on a much lower
level. This may be due to a reduced cleaning effect, because the surfactant
is blocked.
The structure of human hair and its stability are determined
by the cuticle layers and the cortex, which in turn is composed of a variety
of components and layers, down to the alpha-helix.
The protein composition of hair is approximately 65 to 95%. Its moisture is
extremely variable, ranging up to 32% (11). The remaining parts are made up
of lipids, pigments and trace elements. It has always been the objective of
our various studies to simulate the detrimental influences on the hair, and
to develop test methods that can measure improvement or protection against these
damaging effects.
Measurements on hairclippings obtained from the Differential Scanning Calorimeter
(DSC) led to two findings regarding hair. This method measures the energy uptake
and the temperature of the hair. Pre-damaged European hair, during energy uptake
at approximately 150° C was near-constant temperature. That peak is due to
hair denaturation when the hair loses its alpha-helical structural element. At the same time, an analysis of the
peak area provides a measure of cortex resistance. Our study focused only on the
temperature change (12).
When introduced in two different applications on hair (shampoo
and hair rinse), GMO in each case has the effect of increasing the denaturing
temperature. The damaging effect of the surfactants in shampoo is compensated,
and at 149° C the temperature is almost the same as when treated with water
only. A hair rinse even beats the treatment with pure water, the corresponding
denaturing temperature of over 150° C being significantly higher. Temperatures
this high are hardly found anywhere in every day routine. However, when using
a hair drier close to the hair, relatively high temperatures can result. Regular
use of a hair drier in combination with all the other environmental influence,
the hair is damaged. Dry, rough and brittle hair and split ends are the results.
Finally, let us look at the results from simultaneous half-head tests carried
out at the hair stylist's. Two shampoo formulas (with and without EGDS) were applied
to either side of the test person's head. The assessment was left up to the expert
who carried out the test.
Any soiling of the hair becomes evident after pre-washing,
reducing the care substance, washing performance and foam generation. The lathering
properties and foam stability of the blue line clearly show this. Both criteria
are improved in the main wash cycle. In addition a significantly higher foam
volume becomes apparent, requiring longer rinsing. This is quite understandable
due to the improved foam volume in comparison to the placebo. Only a slightly
improved combability is noticeable in still damp hair. However, the feel of
the dry hair and its sheen are significantly better. All additional properties
tested are comparable.
The positive properties of an EGDS-containing shampoo are
shown in micrographs in 1000x magnifications.
Bright edges on the cuticula are recognizable (left micrograph),
they result from the non-use of EGDS. By contrast, the cuticle layers in the
other image are close fitting, illustrating the outstanding surface effects
achieved with EGDS.
To sum up, the positive effects achieved on skin and hair
were confirmed in our various tests. The improved revitalisation effects on
hair and hair structure may be proved by objective as well as subjective results,
including effects that can be seen and felt.
Summary
The esters presented may be applied in skin and hair cleansing formulas and
show good effects here. Effective clear formulas may only be produced from Glyceryl
Oleate (GMO). Turbid formulas may only be produced from Cetyl Palmitate (CP)
or Glycol Distearate (EGDS). Turbid wax dispersions must have a fine-disperse
wax structure in order to produce appreciable effects. A variation in the amounts
used makes it possible to balance the effects especially with the wax dispersions.
This formulating technology provides sufficient possibilities for generating
the desired effects from the formulations.
Acknowledgements
Compiling the results here presented required a large number
of different tests and discussions that helped us understand the effects and
to learn. For this I wish to express my thanks to my colleagues from the departments
of applied technology and performance testing, without whose contributions a
comprehensive presentation like this would not have been possible.
* Lamesoft PO 65, Lamesoft PW 45 and Lamesoft TM Benz are registered trademarks of Cognis
Deutschland GmbH & Co KG.
This topic was presented at Personal Care Europe Exhibition in Paris, February
2002.
Author
Werner Seipel joined the cosmetic industry in 1980, after completing his professional
training as a chemical engineer. He started out at the laboratories for applied
chemistry at Lingner & Fischer, Germany. Since 1989 he has been head of
a laboratory for applied technology and in charge of developing new raw materials
in the field of hair and body cleansing products at Henkel, Düsseldorf.
With the formation of Cognis Germany at the end of 1999 he took over responsibility
for application and technical services in the cosmetic market segments Hair,
Body, Oral Care in the Care Chemicals Division.
References
(1) V. R. Wheatley; The Physiology and Pathophysiology of the
Skin Vol. 9 The Sebaceous Glands;Academic Press 1986 Harcourt Brace Jovanovich,
Publishers
(2) S. El Gammal; Hoch auflösende Sonographie; AP Dermatologie; 5/September-October
2001; pp. 12 - 13
(3) W. Both, P. Busch; Torsion measurement as a means of assessing
skin characteristics; SÖFW Journal (1998) 182 - 195
(4) M. Rohr und K. Schrader, Fast Optical In vivo Topometry of Human
Skin (FOITS), SÖFW-Journal, 124: 2 (1998) 52 - 59
(5) DIN 4768 Ermittlung der Rauheitskenngrößen Ra, Rz, Rmax mit elektrischen
Tastschnittgeräten, Begriffe, Meßbedingungen
(6) F. Franconi; Measurement of epidermal moisture content
by magnetic resonance imaging; British Association of Dermatologists 1995 132,
913 - 917
(7) M. Takenouchi, H. Suzuki and H. Tagami; Hydration Characteristics
of Pathologic Stratum Corneum-Evaluation of Bound Water; The Society for Investigative
Dermatology, Inc. ; Vol. 87, No 5 November 1986, 574-576
(8) T. Yamamura and T. Tezuka; The Water-Holding Capacity of
the Stratum Corneum Measured by 1H-NMR; The Society for Investigative
Dermatology, Inc. ; Vol. 93, 1, November (1989)160 - 164
(9) R. F. Stamm, M. K. Garcia, J. J. Fuchs: The optical properties of
human hair I. Fundamental considerations and goniophotometer curves, J. Soc.
Cosmet. Chem. 28; September (1977) 571 - 599
(10) R. F. Stamm, M. K. Garcia, J .J. Fuchs: The optical properties of
human hair II. The luster of hair fibers, J. Soc. Cosmet. Chem. 28 (September),
601-609, (1977)
(11) H. Deutz; Thermische und mikroskopische Charakterisierung von Keratinen;
TH Aachen H94 B 1479
(12) P. Morganti, G. Morganti; Hair and Cosmesis; SOAP &
Cosmetics; September 2001, 26 - 31
