Open Journal of Applied Sciences, 2012, 2, 139-145
doi:10.4236/ojapps.2012.23020 Published Online September 2012 (http://www.SciRP.org/journal/ojapps)
Stability Study of O/W Cosmetic Emulsions Using
Rosmarinus officinalis and Calendula officinalis Extracts
Evi-Maria Varka, Eforia Tsatsaroni*, Nikolet a Xristoforidou, An na - Ma ri a Dard a
Department of Chemical Technology and Industrial Chemistry, School of Chemistry, Aristotle University, Thessaloniki, Greece
Received May 20, 2012; revised June 21, 2012; accepted July 10, 2012
ABSTRACT
Cosmetic emulsions, as all macro emulsions, are inherently unstable systems, from a thermodynamic viewpoint. More
specific eco-friendly oil/water (O/W) cosmetic emulsions are usually less stable than conventional ones as milder
chemicals or less intense (energy consuming) production processes are involved. In this context, two traditional tech-
niques an optical technique and a volumetric one have been used for the assessment of the stability of cosmetic emul-
sions and compared to each other. Eco-friendly cosmetic emulsions were produced with different olive oil/water ex-
tracts (Rosmarinus officinalis and Calend ula officin alis extracts) and emulsifier (Glycerol monostearate, GMS) concen-
trations. Emulsions’ stability was registered simultaneously by 1) Microscopy photos of samples withdrawn at regular
intervals from the test vessel; 2) Global volumetric measurements of the different phases (water/oil/emulsion) inside the
test vessel made at regular intervals for determining the evolution of the location of the phases separation interface.
Analysis of the results of each technique and comparisons among them are presented and discussed in detail.
Keywords: Cosmetic Emulsions; Olive Oil; Stability Studies; Rosmarinus officin alis; Calendula officinalis
1. Introduction
Since antiquity, emulsions have been used in cosmetics.
In contrast to pharmaceutical ointments which must pe-
netrate deep into the skin, cosmetic products are meant
only for the immediate surface of the skin i.e. the epi-
dermis. However, many commercial cosmetic products
contain artificial chemicals that inevitably penetrate the
skin. In the last few years physical products have started
to gain the interest of consumers. Because of the incon-
siderate use of chemical components and the harmful
consequences of them in peoples’ health, scientists
started to look out for alternative findings to surpass
these problems. For this reason herbs’ study has gained
attention [1-4].
Eco-friendly cosmetics—also known as organic cos-
metics-appeared in the early 1900s. The biggest advan-
tage of organic cosmetics is that they are safe for humans
and the environment as they do not contain toxic chemi-
cals, they need no animal testing and their results can be
as pleasing as those achieved by commercial products.
Rosmarinus officinalis L. (Lamiaceae), commonly known
as rosemary, is a household plant used worldwide as a
food-flavouring agent, widely distributed in the Mediter-
ranean region. A preclinical survey confirmed that rose-
mary has powerful anti-inflammatory, antibacterial, anti-
diabetic, antitumor, cytoprotective and hepatoprotective
properties [5-10]. Rosemary has one of the highest anti-
oxidant activities of all the herbs and spices that have
been investigated [11]. The antioxidant activity of rose-
mary justifies its use in a broad range of applications,
including food preservatives [12], cosmetics [13], phy-
tomedicines etc. These properties attributes can be re-
lated to rosemary’s high content of polyphenolic com-
pounds, especially rosmarinic acid [14], which is con-
sidered a chemical marker of this species.
Calendula officinalis L. (Asteraceae), also known as
marigold, is an annual herb native to the Mediterranean
region. It is cultivated for ornamental and medicinal
purposes in Europe and America. More than 35 proper-
ties have been attributed to the decoctions and tinctures
from the flowers, e.g. anti-inflammatory, analgesic, bac-
tericide, tonic and the healing of wounds and skin erup-
tions [15]. Previous phytopharmacological studies on the
extracts of Calendula officinalis flowers have confirmed
the presence of bioactive secondary metabolites, flavonol
glycosides [16,17] and triterpenoids [18].
From the above we can see that traditional herbs pro-
vide an interesting, largely, unexplored source for de-
velopment of potential new cosmetics. In the present
study we tried to combine all this beneficial components
of the herbs in order to make O/W emulsions.
The oil being used was olive oil. Olive oil is natural oil
*Corresponding author.

E.-M. VARKA ET AL. 140
typically used in cosmetics and foods. Apart from being
a natural and hypo allergic way to moisture skin, extra
virgin olive oil has the extra advantage of containing
strong antioxidants, like vitamins A and E. The antioxi-
dants help repairing and renewing skin that has been
damaged from overexposure to sun, air pollution and
other environmental hazards. The selected emulsifier was
GMS which is an eco-friendly emulsifier widely used in
lotions, creams powders etc. as it is safe for humans and
gives skin a soft and smooth appearance, while the water
phase was deionized water.
A series of emulsions was made with different oil or
water phase from the above extracts and their stability
was studied. Emulsions’ stability was registered simul-
taneously by 1) Microscopy photos of samples with-
drawn at regular intervals from the test vessel or deter-
mining the evolution of the local droplet size distribution;
2) Global volumetric measurements of the different pha-
ses (water, oil) inside the glass tubes for determining the
evolution of the phase’s separation.Additionally, pH,
surface/interface tension measurements were also made.
Analysis of the results of each technique and compare-
sons among them are presented and discussed in detail.
2. Materials and Methods
2.1. Materials
The plant materials Rosmarinus officinalis and Calen-
dula officinalis, were collected at the bloom stage at the
end of May. The plant material was dried at room tem-
perature and then milled. The dry plant material was then
packed in paper bag and kept in a dark, dry and cool
place.
Greek olive oil was obtained by “Altis S.A.” whereas
Glycerol monostearate (GMS), an esterification product
of glycerine and stearic acid was obtained from Panreac
(purity > 98%) and used as emulsifier.
2.2. Plant Material Extractions (Oil/Water
Phases)
Plant materials (Rosmarinus officinalis and Calendula
officinalis), were placed separately in a vessel with olive
oil in a proportion of 10%. The material was warmed up
for 5 minutes and then was kept in a dry place for 40
days approximately in order to have a complete extrac-
tion. The remaining oils were used as oily extracts.
Water extracts, where needed, were taken by inserting
herbs (Rosmarinus officinalis and Calendula officinalis)
into boiled water for 10 minutes in a proportion of 10%.
2.3. Emulsification Process
Emulsification was implemented by mixing water or wa-
ter extract with olive oil or oil extract using an impeller
rotating at the central axis of a glass vessel with internal
diameter of 9.5 cm. The impeller was placed 1.0 cm
above the bottom of the vessel and not at the traditional
(for mixing applications) 1/3 of the vessel height. Four
buffles were placed at 90 degrees intervals around the
vessel in order to allow high rotation speeds without
vortexing and air suction. Emulsions were prepared in
the above glass vessel as follows. Initially, proper
amount of GMS (Tables 1, 2) was added to the 20 ml of
oil and then the mixture was heated to 70˚C (GMS is
solid at ambient temperature). The corresponding amount
of aqueous solution 80 ml was heated separately to 70˚C.
Emulsification started by adding the hot aqueous phase
into the hot oil. At that moment heat supply was turned
off and agitation was set at 700 rpm. The impeller was
running at 700 rpm, for a total 1.5 min. This period was
followed by 30 more minutes of agitation at 700 rpm
which was sufficient for the emulsion to cool down to
ambient temperature (25˚C ± 1˚C).
2.4. Creaming Index from Volumetric
Measurements
Direct optical observations were employed to determine
the instantaneous heights of the emulsion and of the aque-
ous phase inside the glass vessel (Figure 1) and to esti-
mate the creaming index according to the formula (Equa-
tion (1)):
100
aq
tot
H
CI H  (1)
Table 1. Oil-to-water types of Rosmarinus officinalis emul-
sions and concentration of GMS in the oily phase used for
emulsion preparation.
Type of emulsions 4.5 g GMS 6 g GMS
O/Wa √b √
O/R √ √
R/W √ √
R/R √ √
Table 2. Oil-to-water types of Calendula officinalis emul-
sions and concentration of GMS in the oily phase used for
emulsion preparation.
Type of emulsions 3 g GMS 4 g GMS
O/W √ √
O/C √ √
C/W √ √
C/C √ √
a. O/W: always the first letter denotes oily phase whereas the second one the
water phase; R: Rosmarinus officinalis extracts; C: Calendula officinalis
extracts. b. √: denotes the emulsions being made.

E.-M. VARKA ET AL. 141
Creaming index, CI, represents the instantaneous global
(i.e. the whole liquid volume) volumetric water fraction.
It is the most customary measure of emulsion destabili-
zation reflecting phase separation (Figure 1).
siometer. The platinum plate was partially immersed into
the oil layer, where it remained to fixed position during
the course of the experiment. Thus, the surface tension
decreased as a function of time. When the surface tension
was stabilized then the experiment was stopped. For the
interfacial tension measurement Ring Du Nouy method
was used. A ring from platinum was going down and
immersed into the water phase. Then carefully the oily
phase was being placed from the top of the water one.
The ring was pulling up until the lamella from the inter-
face breaks off. At this point the measured force gives
interfacial tension value. This method has an easy han-
dling, big accuracy and does not depend on wetting con-
tact angle. All measurements were made at 25˚C ± 0.1˚C.
2.5. Droplets Size from Microscope Photos
Several photos were taken by the microscope from dif-
ferent parts of the withdrawn samples until a population
above 300 droplets was collected for each sample in or-
der to ensure statistical significance in the determination
of droplets size. A custom made software capable of
handling even very dense emulsions was employed to
obtain droplet diameter distributions and from them to
acquire droplet size distributions (Figure 2).
2.6. Additional Measurements 3. Results and Discussion
2.6.1. pH Measurements 3.1. Creaming Index
pH measurements were made by dipping into the emul-
sion the pH sensor of a WTW pH 535 microprocessor. Figures 3 and 4 present the computed creaming index for
Rosmarinus officinalis/Calendula officinalis oil-in-water
cosmetic emulsions respectively.
2.6.2. Su rface/I n te rface Tension Me a s u rements The higher the creaming index value is, the more de-
stabilized the emulsion is. In our occasion maximum
The surface tension measurements were taken with the
Wilhelmy plate technique using a KSV Sigma 70 ten-
Aqueous Phase H
aq
H
total
(a) (b)
Figure 1. (a) Glass vessels being employed for the determination of creaming index value according to scheme (b).
Figure 2. Schematic representation of estimating droplet diameter distributions.

E.-M. VARKA ET AL. 142
value proportion of water is 80%. There are two general
features in the evolution of creaming index: 1) as oil
phase is enriched with oil extract, creaming rate de-
creases; 2) as emulsifier concentration increases, cream-
ing rate decreases.
More specific, Figure 3 represents creaming index
value for Rosmarinus o fficinalis emulsions. For an emul-
sion with 6 g GMS and Rosmarinus officinalis oil extract
no sign of creaming was observed for the first 60 days
after production. Yet, all other examined cases show
some variability with time although none of the emul-
sions reached the value of 80% representing the complete
separation. Probably the emulsions were stabilized after
having a metastable form. Separation of the two phases
was almost complete in less than 20 days in the emul-
sions with no addition of extracts, regardless GMS con-
centration.
Same trends are also observed in Figure 4. Separation
of the two phases was almost complete in less than 5
days in the emulsions with no addition of extracts.
Comparing Figures 3 and 4 the following comments
can be made 1) Emulsions made up with Calendula offi-
cinalis extracts are more stable than those made with
Rosmarinus officinalis due to lower values of creaming
index (results were not changed up to 30 days for Ca-
lendula officinalis emulsions) 2) emulsions having oily
extracts were the most stable in both cases.
3.2. Droplet Size Distributions
Results obtained from the analysis of the microscope
photographs are presented in Figures 5 and 6. The mean
diameter of the emulsion from samples is shown against
the GMS concentration for the two emulsion types. In
accordance with stability results from volumetric meas-
urements the following are concluded: 1) droplet size
decreases as GMS concentration increases and also as
emulsions are enriched with herbal extracts. One would
expect that droplet sizes would be smaller for emulsions
made up with 6 g GMS instead of 3 and 4 g. Although
data points for the two emulsion compositions are close
enough and can be considered comparable given the sta-
tistical lack of confidence (at a 95% level), on the other
hand; 2) different herb components may affect the total
results. In terms of droplet size Calendula officinalis’
emulsions present better stability (smaller droplets) than
CI%
0 20 40 60
t, Days
50
45
40
35
30
25
20
15
10
5
0
O
/
W 4.5 0
O/R 4.5 0
R/W 4.5 0
R/R 4.5 0
CI%
0 20 40 60 80
t, Days
12
10
8
6
4
2
0
O/W 6.0
O/R 6.0
R/W 6.0
R/R 6.0
(a) (b)
Figure 3. Creaming index versus time for Rosmarinus officinalis extract with (a) 4.5 g GMS and (b) 6 g GMS (where O: Olive
oil; W: water; R: Rosmarinus officinalis oil and water extract).
0 5 10 15 20
days
35
30
25
20
15
10
5
0
O/W(3.0)
C/W(3.0)
O/C(3.0)
C/O(3.0)
CI%
0 5 10 15 20 25 30 35
days
18
16
14
12
10
8
6
4
2
0
O/W(4.0)
O/C(4.0)
C/W(4.0)
C/C(4.0)
CI%
(a) (b)
Figure 4. Creaming index versus time for Calendula officinalis extract with (a) 3 g GMS and (b) 4 g GMS (where O: Olive oil;
W: water; C: Calendula officinalis oil and water extract).

E.-M. VARKA ET AL. 143
3 3.5 4 4.5 5 5.5 6 6.5
GM S concentration,g
45
40
35
30
25
20
15
10
5
0
O/W
O/W
O/R
O/R
R/W
R/W
R/R
R
/
R
d,
μ
m
Figure 5. Effect of GMS concentration in mean droplet diameter in Rosmarinus officinalis emulsions.
2 3 4 5 6
GM S concentration,g
45
40
35
30
25
20
15
10
5
0
O/W
O/W
O/C
O/C
C/W
C/W
C/C
C
/
C
d,μm
Figure 6. Effect of GMS concentration in mean droplet diameter in Calendula officinalis emulsions.
those of Rosmarinus officinalis’ emulsions. In accor-
dance with creaming index results Calendula officinalis
emulsions are more stable.
3.3. pH Measurement
In Figures 7(a) and (b) the effect of storage on the pH
values of the emulsions is given. As expected, in both
types of emulsions as oil and/or water extract is added,
pH decreases and this due to different active ingredients
of herb extracts. The emulsions with Calendula Offici-
nalis present a remarkable pH stability with time (Fig-
ure 7(b)). The emulsions with Rosmarinus officinalis
extracts are not as pH stable as those with Calendula
officinalis.
3.4. Surface—Interface Tension Measurements
The low values of interfacial tensions between oil ex-
tracts and water extracts (Tables 3-5) are in line with
results obtained from optical monitoring and volumetric
measurements. The lower the interfacial tension is, the
more stable the emulsion will be. The droplet size distri-
bution resulting from the emulsification procedure is the
outcome of the simultaneous processes of coalescence
between droplets and droplet breakage. The presence of

E.-M. VARKA ET AL. 144
0 5 10 15 20 25 30 35
t, Days
10
9
8
7
6
5
4
O/W 4.5 0
O/W 6 0
O/R 4.5 0
O/R 6 0
R/W 4.5 0
R/W 6 0
R/R 4.5 0
R/R 6 0
pH
(a)
0 5 10 15 20 25
t, Days
9
8.5
8
7.5
7
6.5
6
5.5
5
4.5
4
C/C(3.2)
C/C(3.1)
C/C(3.0)
C/W(3.2)
C/W(3.1)
C/W(3.0)
O/C(3.2)
O/C(3.1)
O/C(3.0)
O/W(3.2)
O/W(3.1)
O/W(3.0)
p
H
(b)
Figures 7. Results obtained from pH meter.
Table 3. Surface tensions of olive oil.
Temperature (˚C) Surface Tension (mN/m)
Olive oil 25 ± 0.1 20
H2O 25 ± 0.1 71.8
Table 4. Interfacial tensions olive oil/Rosmarinus officinalis
oils.
Temperature
(˚C)
Interfacial Tension
(mN/m)
Olive oil-H2O 25 ± 0.1 17
Olive oil-Water extract 25 ± 0.1 6
Olive oil extract-H2O 25 ± 0.1 14
Olive oil extract-Water extract 25 ± 0.1 6
Table 5. Interfacial tensions olive oil/Calendula officinalis
oils.
Temperature
(˚C)
Interfacial Tension
(mN/m)
Olive oil-H2O 25 ± 0.1 17
Olive oil-Water extract 25 ± 0.1 5
Olive oil extract-H2O 25 ± 0.1 13
Olive oil extract-Water extract 25 ± 0.1 6
surface active components in herbal extracts reduces the
coalescence process (stabilizing the water film between
colliding droplets) and enhances the breakage process
due to the reduction of the effective interfacial tension of
the droplet. The combination of these effects results in
the production of smaller droplets (more stable emul-
sions), as interfacial tension decreases.
Conclusively, comparison of the two herbs, Rosmari-
nus officinalis and Calendula officinalis, results in the
following: 1) The effect of Calendula officinalis extracts
is stronger than those of Rosmarinus officinalis. Less
amount of GMS result in more stable emulsions; 2) The
emulsion stability evaluated from factors such as Cream-
ing Index, volumetric index for Calendula officenalis
emulsions reveals more stability than those referred to
Rosmarinus officinalis.
4. Conclusion
In the present work, two experimental techniques were
used for the assessment of the stability of oil-in-water
cosmetic emulsions produced with different herbs and
surfactant concentrations. Results from two classical
techniques (the well known volumetric measurement of
phase separation and the optical measurement of droplet
diameters from withdrawn samples) were examined and
compared to each other. The droplet sizes estimated from
optical observations of the droplets were in accordance
with results obtained by interfacial tension measurements
referring that emulsions made up with Rosmarinus offi-
cinalis are less stable than those of Calendula o fficinalis.
The results and their discussion in this work reveal that
the addition of herbs in cosmetic emulsions can improve
emulsions’ stability without further addition of chemical
stabilizers.
5. Acknowledgements
The authors wish to thank Professor T. D. Karapantsio
for his kind permission to use his custom made software
for the estimation of droplet sizes.
REFERENCES
[1] T. Aburjai and F. M. Natsheh, “Plants Used in Cosmet-
ics,” Phytotherapy Research, Vol. 17, No. 9, 2003, pp.
987-1000. doi:10.1002/ptr.1363
[2] K. H. Wang, R. D. Lin, F. L. Hsu, Y. H. Huang, H. C.
Chang, C. Y. Huang and M. H. Lee, “Cosmetic Applica-
tions of Selected Traditional Chinese Herbal Medicines,”
Journal of Ethnopharmacology, Vol. 106, No. 3, 2006, pp.
353-359. doi:10.1016/j.jep.2006.01.010
[3] H. R. Smith, D. K. B. Armstrong, D. Holloway, L. Whit-
tam, D. A. Basketter and J. P. McFadden, “Contact Der-
matitis and Allergy Skin Irritation Thresholds in Hair-
dresses; Implications for the Development of Hand Der-

E.-M. VARKA ET AL. 145
matitis,” British Journal of Dermatology, Vol. 146, No. 5,
2002, pp. 849-852.
doi:10.1046/j.1365-2133.2002.04718.x
[4] M. Regnier, C. Duval and R. Schmidt, “Potential Cos-
metic Applications of Reconstructed Epidermis,” Interna-
tional Journal of Cosmetic Science, Vol. 21, No. 1, 1999,
pp. 51-58. doi:10.1046/j.1467-2494.1999.183571.x
[5] J. Benincá, P. Dalmarco, M. G. Pizzolatti and T. S. Fröde,
“Analysis of the Anti-Inflammatory Properties of Rosma-
rinus officinalis L in Mice,” Food Chemistry, Vol. 124,
No. 2, 2011, pp. 468-475.
doi:10.1016/j.foodchem.2010.06.056
[6] O. Yesil-Celiktas, E. E. Hames Kocabas, E. Bedir, F.
Vardar-Sukan, T. Ozek and K. H. C. Baser, “Antimicro-
bial Activities of Methanol Extracts and Essential Oils of
Rosmarinus officinalis, Depending on Location and Sea-
sonal Variations,” Food Chemistry, Vol. 100, No. 2, 2007,
pp. 553-559. doi:10.1016/j.foodchem.2005.10.011
[7] T. Bakirel, U. Bakire, O. Keles, S. G. Ülgen and H.
Yardibi, “In Vivo Assessment of Antidiabetic and Anti-
oxidant Activities of Rosemary (Rosmarinus officinalis)
in Alloxan-Diabetic Rabbits,” Journal of Ethnopharma-
cology, Vol. 116, No. 1, 2008, pp. 64-73.
doi:10.1016/j.jep.2007.10.039
[8] S. Cheung and J. Tai, “Anti-Proliferative and Antioxidant
Properties of Rosemary Rosmarinus officinalis,” Oncol-
ogy Reports, Vol. 17, No. 6, 2007, pp. 1525-1531.
[9] K. Yoo, C. H. Lee, H. Lee, B. Moon and C. Y. Lee, “Rela-
tive Antioxidant and Cytoprotective Activities of Com-
mon Herbs,” Food Chemistry, Vol. 106, No. 3, 2008, pp.
929-936. doi:10.1016/j.foodchem.2007.07.006
[10] R. Gutiérrez, J. L. Alvarado, M. Presno, O. Pérez-Veyna,
C. J. Serrano and P. Yahuaca, “Oxidative Stress Modula-
tion by Rosmarinus officinalis in CCl4-Induced Liver
Cirrhosis,” Phytotherapy Research, Vol. 24, No. 4, 2010,
pp. 595-601.
[11] A. Wojdyło, J. Oszmiański and R. Czemerys, “Antioxi-
dant Activity and Phenolic Compounds in 32 Selected
Herbs,” Food Chemistry, Vol. 105, No. 3, 2007, pp. 940-
949. doi:10.1016/j.foodchem.2007.04.038
[12] K. Hamre, K. Kolås and K. Sandnes, “Protection of Fish
Feed, Made Directly from Marine Raw Materials, with
Natural Antioxidants,” Food Chemistry, Vol. 119, No. 1,
2010, pp. 270-278. doi:10.1016/j.foodchem.2009.06.024
[13] C. J. Lee, L. Chen, T. Chang, W. M. Ke, Y. F. Lo and C.
C. Wang, “The Correlation between Skin-Care Effects
and Phytochemical Contents in Lamiaceae Plants,” Food
Chemistry, Vol. 124, No. 3, 2011, pp. 833-841.
doi:10.1016/j.foodchem.2010.07.003
[14] N. Erkan, G. Ayranci and E. Ayranci, “Antioxidant Ac-
tivities of Rosemary (Rosmarinus officinalis L.) Extract,
Blackseed (Nigella sativa L.) Essential Oil, Carnosic
Acid, Rosmarinic Acid and Sesamol,” Food Chemistry,
Vol. 110, No. 1, 2008, pp. 76-82.
doi:10.1016/j.foodchem.2008.01.058
[15] J. A. Duke, “Handbook of Medicinal Herbs,” CRC Press,
Boca Raton, 1991.
[16] P. Pietta, A. Bruno, P. Mauri and A. Rava, “Separation of
Flavonol-2-O-Glycosides from Calendula officinalis and
Sambucus nigra by High-Performance Liquid and Micel-
lar Electrokinetic Capillary Chromatography,” Journal of
Chromatography, Vol. 593, No. 1-2, 1992, pp. 165-170.
doi:10.1016/0021-9673(92)80282-Y
[17] E. Vidal-Olliver, R. Elias, F. Faure, A. Babadjamian, F.
Crespin, G. Balansard and C. I. Boudon, “Flavonol Gly-
cosides from Calendula officinalis Flowers,” Planta
Medica, Vol. 55, No. 1, 1989, pp. 73-74.
doi:10.1055/s-2006-961831
[18] R. Loggia, A. Tubaro, S. Sosa, H. Becker, S. T. Saar and
O. Isaac, “The Role of Triterpenoids in the Topical Anti-
Inflammatory Activity of Calendula officinalis Flowers,”
Planta Medica, Vol. 60, No. 6, 1994, pp. 516-520.
doi:10.1055/s-2006-959562