134 New cosmetic science

5.2.5. Other surfactants

5.2.5. J. Polymeric su份ctants

Many early surfactants contained about 10一 18 carbon atoms as the hpophilic group and
had a molecular weight of about 300. If ethylene oxide propy1eneoxide block polymers
are combined with many polyoxyethylene , it is possible to obtain a molecule with a
weight of 1000-2000 but normally the molecular weight is less than 1000.
Based on this , polymeric surfactants could be described as surfactants with a high
molecular weigh t. For example , polyvinyl alcohol can be made into fiber and film but
when it is used for the action of emulsification or coagulation , it could easily be de-
scribed as a polymeric surfactan t. Based on this concept, sodium alginate , starch deriva-
tives , and tragacanth gum , etc. , can be used as emulsifiers , flocculants and dispersants.

5.2.5.2. Natural surfactants

Lecithin is a well-known natural surfactant combining the anionic groups of phosphate
esters with the cationic groups of quatemary ammonium salts. Lecithin is obtained from
soy beans and egg yolks and the main components are phosphatidyl serine , phosphatidyl
ethanolamine , phosphatidyl choline. In cosmetic applications , lecithin is used În milky
lotions and creams because it has a refreshing feeling on use and softening properties.
Recently , lecithin has been used to form liposomes which have a bilayer membrane.
Many other natural surfactants have long been known and used including lanolin ,
cholesterol and saponin.

5.3. Humectants
Maintaining a young-Iooking skin is c1 0sely connected with moisture content I7 , 18J. One
of the most important functions of cosmetics is maintaining skin moisture I6 ).
The keratin layer of the skin contains natural moisturizing factors I9-2J ) (NMF) with
hydrophilic moisture absorbing compounds; NMFs are known to play an important role
in skin moisturizing (Table 5.1). It is believed that the sodium salt of sodium pyrrolido-
necarboxylate is the most important factor in NMFJ6, 17J.
NMF is not the only important factor in considering skin moisture; it is also important
to consider preventing loss by bonding or surrounding, the presence of oils such as
intercellular lipids and sebum controlling moisture evaporation , and holding water , the
presence of mucopolysaccharides in the dermis. Cosmetics should be able to mimic this
natural moisture retention mechanism. Humectants are water soluble materials with a
high water absorption and they are a very important component in the aqueous phase of
cosme tJ cs.
A wide variety of humectants are used in cosmetics including polyhydric alcohols Iike
glycerin , propylene glycol , sorbitol , and including the main component of NMF , pyr-
rolidonecarbonate and lactates. Recent advances in biosynthesis technology has also
permitted production and use of large amounts of sodium hyaluronate. As described pre-
VIOUS旬， humectants play an important role in cosmetics but at the same time they also
work to maintain the moisture content and stabilize the cosmetic itsel f. In addition , they
also have bacteriostatic and fixative activities.
 Raw materials 0/ cosmetics 135

Table 5. 1. Comp的iüon ofNMF I 9.20)

Aminú acids 40%

PCA (pyrrolidone carbox ylic acid) 12%
Lactates 12 %
U~ 7%
NH ". uric acid. glucosamine. creatinine 1.5%
Citrates 0.5%
Na 5% . K 4%. Ca 1.5%. Mg 1. 5%. 1'0 , 0.5%. CI 6% 18.5%
Sucrose. organic acids , peptides. other materials 8.5%
(0. 1\.. J ac的 bi : Proc. Sci. Sec. () f Toilet C 圳 l d s Assoc. , 31, 22可 1959.)
(H.W. Spiet , G. l' ascher : Hautarzt, 7.2. 1 的6.)

The main requirements of a humectant are listed below:

(1) must have appropriate water absorption ability
(2) must maintain water absorption ability
(3) water absorption must not be influenced by changing environmental conditions
(temperature , humidity , etc.)
(4) water absorption ability must maintain moisture in skin
(5) must have lowest possible volatility
(6) must have good miscibility with other constituents
(7) must have lowest possible freezing point
(8) viscosity must match usage and feel good on skin
(9) must be safe
(10) must be as colorless , odorless and tasteless as possible
In addition to having water absorption and moisturizing properties over a wide range
of humidities , humectants must have densities matching the system they are used in.
Even when the humectant is used incorrectly , the correct functions must sti l1 be main-
tained and reverse effects should not be possible.

5 .3 .1. Glycerin

CH , OH
CHOH
CH ,OH

Glycerin has long been used as a humectant and it is still widely used even today . It is
obtained as a byproduct in manufacturing soap or fatty acids from plant and animal fats
and oils. When dehydrated and deodorized , it is a colorless , odorless liquid.

5 .3.2. Propylene glycol

CH ,
CHOH
CH ,OH
136 New cosmetic science

The common form is 1,2-propylene glyco l. Although it looks and feels much like glyc-
erin and is colorless and odorle蹈， it has a better feeling on use due to its lower viscosity
than glycerin.

5.3 .3. 1,3-Butylene glycol: CH_~CH(OH)CH2CH20H

1,3-Butylene glycol is obtained by hydrogenation of the aldol condensate of acetoalde-

hyde as a colorless , odo r1 ess liquid. It is very safe and is used in creams and milky 10-
tlons , etc.

5 .3.4. Polyethylene glycol: HO(CH2CH20)nH

Polyethylene glycol is obtained by adding ethylene oxide to water or ethylene glycol

under alkaline conditions. It is not a uniformly simple compound but is a mixture poly-
mer with various degrees of polymerization.
It is a liquid at normal temperatures with an average molecular weight ranging from
200 to 600; semi-so Ji d forms have increasing molecular weights ranging from 1000,
1500, 4000 to 6000.
Generally , polyethylene glycol is colorless and odorless and its water absorption abil-
ity decreases with increasing molecular weigh t. It is used in creams , milky lotions , etc.

5 .3.5. Sorbitol

CH 20H

(CHOHl ,

CH 2 0H

This sugar alcohoJ22 l is contained in the juice of apples and peaches , and is a white
odorless solid. It is obtained by reduction of glucose.
In comparison to the previously described humectants , it has lower hygroscopic prop-
erty and it has a humectant effect at low humidity. lt is used in creams , milky lotions ,
toothpastes , etc.

5 .3 .6. Sodium lactate: CHjCH(OH)COONa

Lactates are an impo此ant group of natural humectants occurring in NMF along with
PCA (pyrrolidonecarboxylate)_ They have a higher water absorption ability than the
lower-alcohol types.

5.3.7. Sodium 2-pyrrolidone-5-carboxylate

。人N人r()()N
H
 Raw materials of cosmetics 137

Table 5.2. Water absorption 油

a bi山
lit句
y ofsodium 各
2 -pyrrπ.τ.r叫 i岫
don
恥E蛤
e-5ι-c
臼:ar
昀 bo
慨 xy
抖late
戶 2 J)} 訂叫

Compound 31 % RH 58% RH
Pyrrolidone carboxylic acid <1 <1
Sodium pyrrolidone carboxylate 20 61
Gylcerol (comparison) 13 35
(K. Ladem , R. Spitzer : J. Soc Cosme t. Chem.. 1 8 ， 3后 1 . 1967.)

Sodium 2-pyrrolidone-5-carboxylate is an important humectant component of NMF. It is

the sodium salt of 2-pyrrolidine-5-carboxylate manufactured by dehydration of glutamic
acid and forms an odorless solid ,
It demonstrates excellent hygroscopic and humectant effects and these properties have
been achieved with a salt form (Table 5 .2),

5.3.8. Sodium hyaluronate

COONa CH ,OH
可正一一0. ,...__ _ H 正一一O. ~
V且"'J ~U 斗/白"叫 -.....0 ...........
、 "OH . /1 仆~口/1
刻 、一一一-V H HO 、一一一-f' H
H OH H NHCOCH 3 I何

Hyaluronic acid is a type of mucopolysaccharide formed by cross-bonding between N-

acetylglucosamine and gluconic acid. It is widely found in connective tissues of mam-
mals as chondroitin sulfate , etc. In connective tissues , its function is to maintain water in
the intercellular spaces and also to maintain the cells in a jelly matrix. In skin , it is be-
Ii eved to maintain smoothness and flexibility and to prevent external mechanical i吋 ury
and bacterial infection. When examining the distribution of acidic mucopolysaccahrides
in the different parts of the skin , more hyaluronic acid exists than chondroitin sulfate and
heparin in the epidermis and dermis. Having moisturizing properties , hyaluronic acid
makes the skin feel nice and moist; it is said that skin lacking moisture develops wrin-
kles due to the shortage of moisturizing hyalouronic acid in the subdermal connective
tlssues.
Hyaluronic acid was extracted from the cockscomb of domestic fowls , but its ex-
tremely high price greatly limited use until recent development of production by micro-
biological techniques provided a relatively low-cost source 23 ,24).
Generally , hyaluronic acid is marketed as sodium hyalurona肥， a white water-soluble
powde r. Properties like viscosity and humectance vary with the molecular weigh t. The
water evaporation constant of a 0.1 % aqueous solution of sodium hyaluronate at 25 0 C
and 50% relative humidity falls with increasing molecular weight but stabilizes at mo-
lecular weights above about 800,00021 ).
In addition , unlike other humectants , sodium hyaluranate is almost unaffected by en-
vironmental humidity (Fig. 5 .1).
138 New cosmetic science

100

(HZEUUED叫
ssfss
咱也

Z樹CC

50
ZgoE

同\。 自
"
身

Moisture absorbance
~ Temperature
Fig.5-1. Comparison of Moisture Absorbance of Humectants
~ Sodium pyrrolidone carboxylate
1:::::-:.1 Glycerine /
C立 Sorbito l
回回 Sodium hyaluronate

Fi g. 5.1. Comparison of moisture absorbance of humectants.

5.4. Polymers
Polymers 24-28 ) used as cosmetic raw materials are basically classified according to usage .
They are mainly used as thickening agents , film formers and resinous powders. In addi-
tion , some polymers are used as humectants and surfactants. Th is section describes only
thickening agents and film formers; the humectants , surfactants and resinous powders
are described in their respective sections.

5.4.1. Thickening agents

Thickening agents are used to adjust the viscosity of products to make them easy-to-use
as well as to maintain the product stability.
For example, they are used to ensure the stability of milky lotions and liquid foundations
by preventing the separation of emulsified pa此icles and powders. Usually , water-soluble
polymers 訂e used as thickening agents. Table 5.3 shows the major classification based on
their origin. They 缸e classified into natural polymers , semi-synthetic polymers (natural
polymers modified by reaction) and synthetic polymers. However, in the past , natural
polymers formed the mainstream led by natural gums. Problems with securing stable
supplies coupled with problems such as variations in viscosity and microbial contamination
led to a change to synthetic and semi-synthetic substitutes. Currently , synthetic thickening
agents are in the majority . Thickening agents have a great effect on the feeling on use