446
FARMACIA, 2008, Vol.LVI, 4
SKIN TOXICITY EVALUATION FOR SOME
SODIUM LAURYL SULPHATE CREAMS.
A DOSE-DEPENDENT RELATIONSHIP FOR
ANIONIC SURFACTANT
SIMONA ARDELEAN1, CRISTINA A. DEHELEAN2*, CODRUŢA ŞOICA2,
BRÂNDUŞA DUMITRIU3, LAVINIA URŞICA1, VICTOR NĂSTASE4
1
Libro pharma S.R.L. Pharmacy, Arad
University of Medicine and Pharmacy Victor Babeş Timişoara, Faculty
of Pharmacy
3
S.C. Biotehnos S.A. Bucharest
4
University of Medicine and Pharmacy Gr.T.Popa Iaşi, Faculty of Pharmacy
*
corresponding author: criscros1973@yahoo.com
2
Abstract
Surfactants represent an auxiliary substance category, as they are used in both
pharmaceutical and cosmetic products; there are demands to analyse the surfactants for
quality and safety.
In the category of tensioactive compounds, the role of anionactive group was reevaluated and the possibilities that confer the safety of the products containing these
ingredients after a long-term utilization were outlined. It is proven that the semisolid forms
containing these emulsifying compounds are of high quality. The frequent use of
tensioactive products leads to the noxiousness study of these compounds and the
establishing of a very exact dose-effect relationship. The study tries to analyse these aspects
of the noxious reactions of surfactants by modern tests: transepidermal water loss (TEWL),
moistening degree, etc. The main conclusion is that tensioactives like sodium lauryl
sulphate can determine important skin toxicity on concentrations higher than 10%.
Rezumat
Agenţii tensioactivi sau surfactanţii reprezintă o categorie de substanţe auxiliare
analizată în prezent din punct de vedere al cerinţelor de calitate şi siguranţă. Ei fac parte din
forme farmaceutice şi cosmetice.
Dintre compuşii tensioactivi, rolul clasei celor anionactivi a fost reevaluat şi s-au
conturat posibilităţile de conferire a siguranţei utilizării pe termen lung a unor produse
finite cu aceşti ingredienţi, fiind demonstrat că formele semisolide realizate cu astfel de
compuşi cu rol emulgator sunt de calitate superioară. Folosirea frecventă a unor forme
finite cu surfactanţi impune analiza nocivităţii cutanate a acestora şi stabilirea unor relaţii
doză-efect biologic foarte exacte. Studiul îşi propune să analizeze aceste aspecte ale
nocivităţii surfactanţilor prin teste moderne: TEWL (transepidermal water loss), hidratare
etc. Concluzia principală este aceea că tensioactivii de tipul laurilsulfatului de sodiu pot
determina o toxicitate importantă asupra pielii la concentraţii peste 10%.



surfactant
cosmetics
skin toxicity
 transepidermal water loss
 sodium lauryl sulphate
FARMACIA, 2008, Vol.LVI, 4
447
INTRODUCTION
Surfactants represent an auxiliary substance category. Being used
in both pharmaceutical and cosmetic products, there are demands to analyse
the surfactants for quality and safety [1,3].
Although surfactants are auxiliary components, they have an
important role in obtaining several pharmaceutical forms (emulsions,
emulsion ointment bases, etc). In order to assure the quality conditions of
these forms, the absorption and activity of some associated active principles
were changed [1,2,3]. In the category of tensioactive compounds, the role of
anionactive group was re-evaluated and the possibilities that confer the
safety of the products containing these ingredients after a long-term
utilization were outlined because it is proven that the semisolid forms with
these emulsifying compounds are of high quality [1,4]. From that group one
of the most used compounds is sodium lauryl sulphate (SLS) or sodium
dodecyl sulphate (SDS) [1,3]. The counterirritant capability of polymers or
proteins on surfactants is well known [1]. The forms with mixtures of
surfactants were also highly developed for an anti-irritant effect [1,7].
Anyway the toxicity of compounds with powerful tensioactive properties
needs to be well observed. The actual analyse of tensioactive agents is
justified by their extended use in cosmetic products [1,3,8]. The frequent
use of tensioactive products leads to the noxiousness studies of these
compounds [1,3].
MATERIALS AND METHODS
For the patches, there were used: occlusive bandages, adhesive
material for fixing the bandage, syringes and paper. The studies were
developed under the ethical principles of the Declaration of Helsinki
concerning testing on human subjects, including confidentiality on all
records and papers. The rights, safety and comfort of tested human subjects
are above all other scientific or social interests [1,4,8,9]. Before getting
involved in such a study, each and every human subject has freely
consented, knowing in detail every aspect of the testing.
Including criteria: human volunteers, who have been informed of
the particularities of the tests and have freely consented to it, clinically
healthy, Caucasians.
Excluding criteria: dermatological diseases which can interfere with
the final evaluation, pregnancy, participation in other simultaneous studies or
in a short period of time, tattoos, sunburns, scars in the tested areas.
448
FARMACIA, 2008, Vol.LVI, 4
Total number of volunteers were 25, 5 volunteers for each group
participated to one category of tested formula.
Also, participants will be excluded from the tested group if:
- they do not follow investigator’s instructions;
- they get ill or traumatized during tests;
- they no longer agree to the study.
Test description. Testing methodology consists of the following
steps: a certain amount of product (2 mL) is applied with a 2 mL syringe on
an occlusive bandage; the occlusive bandage impregnated with the cosmetic
product is applied on the human skin (shoulder or the upper back side);
simultaneously, placebo (no active substances) and positive control (sodium
laurylsulphate) patches are applied on the skin; the three types of samples
are coded and randomly applied by the investigator, in a “single blind” trial;
the occlusive bandage is maintained with no humidity for 24 hours, keeping
under observation any eventual side effect; after 24 hours the occlusive
bandage is removed from the skin and the product is washed away with no
rubbing; all the skin side effects are evaluated (erythema, dryness, edema)
by COLIPA scores, mentioned below; any reaction is observed immediately
and after 30 min, one hour, 24 and 48 hours from the removal of occlusive
bandage; the evaluation is performed by specialized personnel and under the
same light spot.
Evaluation of toxic/irritant potential for tested cosmetic products
are being performed visually – redness and/or dryness of the skin is
evaluated on a scale according to COLIPA scores (Table I).
Table I
COLIPA scores
Erythema
Dryness (appearance of Edema
scuams)
0 = no erythema
0 = no side effect
 = absence of edema
0.5 = minimal erythema 0.5 = dryness of the skin + = presence of edema
without scuames
1 = diffused, spoted, 1 = minor scuams
light redness
2 = reduced, uniform 2 = reduced descuamation
redness
3 = strong, uniform 3 = severe descuamation,
redness
with big scuams
4 = extreme redness
FARMACIA, 2008, Vol.LVI, 4
449
Determination of transepidermal water loss as indicator of skin
toxicity was used as an instrumental method which detects the quantity of
transepidermal evaporated water on surface unit, by evaluation of vapors
gradient (co-ci) in an open room, based on Fick’s diffusion law (J= kD(coci)/h). Transepidermal transportation consists of the crossing of the intact
corneous layer (SC). There are two crossing possibilities: intracellular and
intercellular (through and among corneocytes). The crossing way depends
on the partition coefficient k of the active substance: hydrophilic substances
prefer the intracellular way while the lypophillic substances choose the
intercellular way; in the same time, there are molecules that can go both
ways. This method represents an indirect evaluation of the integrity of the
hydrophilic layer responsible of the barrier function of the skin. There is a
continuous diffusion of water from the human body towards the corneous
layer and from there to the surrounding medium. Small levels of
transepidermal evaporated water show a better function of the skin as barrier
and a smaller loss of natural moistening degree. The barrier function is
easily disturbed by mechanical or chemical problems. TEWL
(transepidermal water loss) measurement will be performed only after using
the products under occlusive bandages for 24 hours. Test type was
noninvasive method of skin analysis, in a “single blind” trial.
The prepared semisolid formula, for evolution TEWL tests were
compared with a similar one reached with a dry birch tree outer bark extract,
1g/100 g cream (Table II). That formula proved a protective activity for skin
[6,10].
Table II
Semisolid formula used for sodium lauryl sulphate test
INGREDIENT TYPE
CONCENTRATION
(mg/100 g base)
Sodium lauryl sulphate (SLS)
xg
Cethylic alcohol
8g
Cocoa butter
7g
Vaseline
25 g
Preservative solution
60 g
RESULTS AND DISCUSSION
First observations about the irritancy potential of semisolid
formulations were visual evaluations. The main tests were: erythema,
desquamation and edema. The results are presented in Table III.
450
FARMACIA, 2008, Vol.LVI, 4
Table III
The evaluation of irritancy potential
(24 h patch tests after COLIPA regulations). A visual evaluation
Tested
sample
Cream
base with
vegetal
extract
Erythema Desquamation Edema % subjects
with the
effects
0
0
75%
SLS 1%
0.5
0
-
80%
SLS 10%
1
0
-
75%
SLS 20%`
3
0
+
80%
Nontreated
witness
0
0
-
100%
Observations
The rest (25%) of the
subjects
presented
slight redness, edema,
which disappeared in
one hour after the
removal of the patch
20% from the tested
subjects presented or
edema, or diffuse
redness, symptoms that
disappeared after 1
hour after removing the
occlusive patches
25% of tested subjects
had edema or diffuse
redness, symptoms that
disappeared 1 hour
after removing the
occlusive patches
The product obviously
irritates the applied
skin surface, erythema
persisted for 24h, and
the edema disappeared
only after minimum 2
hours from the patches
removal
-
From the presented data it can be observed that the concentration of
SLS is very important for the noxious effect on the skin. Concentrations
over 10% are toxic for the skin even in an acute evaluation. The most
evident adverse effects are: persistent erythema, evident edema and no
evident desquamation.
451
FARMACIA, 2008, Vol.LVI, 4
30
25
20
15 TEWL (g/h m 2)
10
5
0
Base
SLS 1% SLS 10% SLS 20%
Nontreat
Figure 1
TEWL values evolution after SLS creams application comparing to a cream base.
A dose-dependent relationship
TEWL general values (figure 1) confirm possible damages and
adverse effects for a semisolid formula with a concentration over 10% of
SLS. TEWL values for a 20% SLS cream are around 30% that represents
important changes in moistening degree of the skin.
The evolutions of TEWL parameters for not very harmful formula
are presented in Table IV.
Table IV
TEWL evolutions for the SLS creams.
A time-dependent relationship for not very noxious concentrations of SLS
Tested
sample
%
TEWL
variation
after
30min
+20%
%
TEWL
variation
after 1 h
%
TEWL
variation
after 3 h
%
TEWL
variation
after 5 h
+20%
+17%
+7.4%
3. SLS 1%
-3.75
+10%
+3%
No
variation
4. SLS
10%
-35%
-70%
-15%
No
variation
1. cosmetic
cream with
1% SLS
and birch
tree extract
Observations
Integrity of hydrolipidic layer
was improved immediately
after cream application
(TEWL decrease with 20%),
effect that doesn’t persist
more than 3 hours.
This concentration of SLS
doesn’t change significantly
the skin barrier function.
It is noticed the hydrolipidic
layer degradation correlating
with an increasing of the
transepidermal evaporated
water in the first hour after
product application and the
activity of some homeostatic
mechanisms.
452
FARMACIA, 2008, Vol.LVI, 4
From the transepidermal water loss (TEWL) variation we may
notice the increasing of variation and a status position after a few hours for
tested creams. Negative values indicated decreasing of moistening degree
and positive values improving of moistening degree by transfer of water
from the cream base. Any formula improved with vegetal extracts that offer
skin protection/hydration leads to increasing of moistening degree.
CONCLUSIONS
Sodium lauryl sulphate (SLS) is a well known surfactant that is
used as a model of irritation. It determines important toxic effects on skin,
dependent on a dose-effect relationship.
Its primary noxious effects consist of erythema and edema.
Concentrations over 10% are very harmful for the skin, in
particular when it is applied as single compound.
Any improving of the formula with protective compounds reduces
the surfactant noxious effect and first of all, TEWL negative variation.
REFERENCES
1. Barel A.O., Paye M., maibach H.I., Handbook of Cosmetic Science
and Technology, 2003, 271-275
2. De Paepe K, Lagarde J-M., Gall Y., Roseeuw D., Microrelief of the
skin using a light transmission method, Arch. Dermatol. Res., 2000,
292, 500-510
3. Dragomirescu A., Dehelean C., Dermatofarmacie si cosmetologie,
Ed. Brumar, Timişoara, 2002, 151-157, 160-172
4. Frosch P.J., Kurte A., Efficacy of skin barrier creams, Contact
Dermatitis, 1993, 28, 154-162
5. Pinnagoda J., Tupker R.A., Agner R., Guidelines for transepidermal
water loss measurement, Contact Dermatitis, 1990, 22, 164-178
6. Patocka J., Biologically active pentacyclic triterpenes and their
current medicine signification, Journal of Applied Biomedicine,
2003, 1, 7 – 12
7. Seiller M., Martini M.C., Formes pharmaceutiques pour application
locale, Technique et Documentation, Paris, 1996
8. York M., Griffiths H.A., Whittle E., Basketter D.A., Evaluation of
human patch test for the identification and classification of skin
irritation potential, Contact Dermatitis, 1996, 34, 202-212
FARMACIA, 2008, Vol.LVI, 4
453
9. Wissing S.A., Muller R.H., The influence of solid lipid nanoparticles
on skin hydration and viscoelasticity –in vivo study–
Eur.J.Pharm.Biopharm., 2003, 56(1), 67-72
10. L.Urşica, C.Dehelean, C. Peev, V.Vlaia, G.Coneac- Formulation and
quality evaluation of some topical semisolid preparations containing
dried extract of birch tree, Recent Developments in Pharmaceutical
Analysis, Sept. 2005, 207.