].Cosmet. Sci., 58, 45-51 CTanuary/February 2007)
Clay facial masks: Physicochemical stability at different
storage temperatures
VIVIAN ZAGUE, DIEGO de ALMEIDA SILVA,
ANDRE ROLIM BABY, TELMA MARY KANEKO, and
MARIA VALERIA ROBLES VELASCO, Department of Pharmacy,
School of Pharmaceutical Sciences, University of Sao Paulo, 580 Prof
Lineu Prestes Av., Bl-13, 05508-900, Cidade Universitciria,
Sao Paulo, SP, Brazil
Accepted for publication September 20, 2006.
Synopsis
Clay facial masks-formulations that contain a high percentage of solids dispersed in a liquid vehicle-have
become of special interest due to specific properties presented by clays, such as particle size, cooling index,
high adsorption capacity, and plasticity. Although most of the physicochemical properties of clay dispersions
have been studied, specific aspects concerning the physicochemical stability of clay mask products remain
unclear. This work aimed at investigating the accelerated physicochemical stability of clay mask formula-
tions stored at different temperatures. Formulations were subjected to centrifuge testing and to thermal
treatment for 15 days, during which temperature was varied from -5.0 ° to 4 5 .0 ° C. The apparent viscosity
and visual aspect (homogeneity) of all formulations were affected by temperature variation, whereas color,
odor, and pH value remained unaltered. These results, besides the estimation of physicochemical stability
under aging, can be useful in determining the best storage conditions for clay-based formulations.
INTRODUCTION
Face mask beauty treatments are among the oldest cosmetic preparations. Current
interest in the development of these formulations is attributed to their warmth, tight-
ening, and cleansing effects. Characteristics such as ease of application and removal,
reduced time for drying and hardening, and dermatological innocuousness are also
required (1-3). One of the most popular face masks is the wash-off type based on clay
raw materials, also known as clay facial masks or the once-fashionable "mud packs" (1).
Cosmetic science and aesthetic medicine have been rekindling interest in clay facial
masks mainly due to clay properties such as particle size, cooling index, high adsorption/
absorption capacity, and plasticity (4-6). Clay facial masks are composed of a high
percentage of solid particles (over 25%) dispersed in a liquid vehicle. The concentration
Address all correspondence to Vivian Zague.
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46 JOURNAL OF COSMETIC SCIENCE
of these particles depends on the compos1t10n of the solids and liquid, and it will
determine the plasticity of the final product (1). Some substances, known as hydrophilic
thickeners, such as gums, can also change plasticity and alter the application character-
istics of the final product. Moreover, such substances may be useful in stabilizing the
dispersion of solids and, consequently, in preventing gradual phase separation, which is
occasionally observed during the shelf storage of clay masks (2). Clay facial masks should
be also formulated so as to prevent a slight or even complete dehydration of the
formulation under aging. Therefore, the inclusion of humectant substances, like glycerin
and propylene glycol, would avoid such dehydration (1).
Clay liquid dispersions involve an assortment of different stages including incorporation,
wetting, the break-down of particle clusters, and flocculation of the disperse particles.
Usually, the stability of the clay dispersion is affected by interactions between liquid and
particles and also by attractive interactions between solid particles (7).
Several authors have studied the effects of size, particle shape, mineralogy, and chemistry
of clays as well as the effects of pH, salt concentration, and mixing conditions on the
final dispersion properties (7-12). To our knowledge this is the first study focusing on
the physicochemical stability of clay mask preparations. Therefore, this study aimed at
predicting the physicochemical stability of clay masks under storage conditions at
different temperatures. This prediction is important in defining the components of
formulation, packing material, cosmetic forms, and preparation techniques (13).
MATERIAL AND METHODS
FORMULA TIO NS STUDIED
The clay facial mask formulations were developed with grade cosmetic raw materials
selected in agreement with technical and scientific specifications suited in relation to
particle size, microbial load, color, and odor.
The formulations were developed with kaolin (30% w/w) and montimorillonite (15%
w/w) (Alban Muller International, Vincennes, France). Formulations F2 and F3 also
contained magnesium aluminum silicate (5% w/w) (R. T. Vanderbilt Inc, Norwalk,
CT). The hydrophilic thickeners were hydroxypropyl starch phosphate (2.0% w/w)
(National Starch &Chemical Company, NJ) (Fl) and xanthan gum (0.2% w/w) (Rhodia
SA, Boulogne-Billancourt, France) (F3). Glycerin (4% w/w) and propylene glycol (4%
w/w) were used as humectants in all formulations.
As the way of preparation has a great influence on the degree of clay dispersity and thus
on the physicochemical stability of the final product, all samples were prepared in the
same way. The clays were weighed and sprinkled into distilled water (at 75 ° -80 ° C)
during continuous stirring for 30 min using a high-shear mixer (model 252-21, Quimis
Ltda, Sao Paulo, Brazil) at 8000 rev/min -1 .The hydroxypropyl starch phosphate gum
was hydrated prior to its addition to the clay dispersion. In the F3 formulation, mag-
nesium aluminum silicate and xanthan gum were blended and then sprinkled into
distilled water in the same manner. The humectants were added in sequence.