Surfactanttype Skin Cleansers

Main surfactants used for surfactant-type skin cleansers are listed in Table 2. Soaps are used as a primary surfactant for solid bar cleansers and paste-type cleansers. Sodium soaps are commonly used for solid bars and potassium soaps are mainly for paste-type cleansers or shaving foams. Opaque soft bar is made from triethanolamine soap as gentle facial cleanser. Soaps have excellent lathering properties and superior detergency but some deposit in hard water and cause skin tightness. Additional surfactants are combined with soap in order to improve tightness and give better mildness. Alkylethersulfate, acylisethionate, acylglutamate, acylmethyltaurate, and acylglycinate are commonly combined as a secondary or tertiary surfactant with soap. Acylglutamate has a unique feature as weakly acidic similar to skin pH surfactant and is thus often used as a primary surfactant to give superb mildness for different formulation types.

As of their physicochemical nature, surfactants not only remove soils but also tend to strip useful substances from the skin. Thus excessive solubilization and stripping of skin lipids and natural moisturizing factors (NMF) must be avoided, otherwise destruction of skin-barrier functions would happen. The composition of skin-surface lipids is listed in Table 3 [3] and composition of constitutive lipids in the stratum corneum is shown in Table 4 [4]. Detergency of surfactant should be good enough to remove surface lipid but not to strip minimally constitutive lipids, which are key components of skin-barrier function. Such selective detergency is found for several surfactants and acylaminoacids such as acylglutamate or acylmethyltaurate, which are relatively better in this regard than soap [5,6]. Composition of NMF is shown in Ref. [7]. Acylglutamate showed less stripping of NMF than soap. [8] Changes of skin pH are dependent on the type of surfactant used too. As shown in Figure 1 and 2, water-holding capacity and skin pH by repeated wash with acylglutamate was not affected much while soap changed these two properties seriously.

Formulations are designed to fit for the specific concept to which a product is aimed along with the general requirement as a skin cleanser such as detergency, feeling, viscosity,

Table 3 Composition of Human Skin Surface Lipids

Average

Table 3 Composition of Human Skin Surface Lipids

Average

Triglycerides

41.0

19.5-49.4

Diglycerides

2.2

2.3-4.3

Fatty acids

16.4

7.9-13.9

Squalene

12.0

10.1-13.9

Wax esters

25.0

22.6-29.5

Cholesterol

1.4

1.2-2.3

Cholesterol esters

2.1

1.5-2.6

Table 4 Composition of Constitutive Lipids in the Stratum Corneum

Lipid

Wt%

Cholesterol esters

1.7

Triglycerides

2.8

Fatty acids

13.1

Cholesterol

26.0

Ceramides

45.8

Glucosylceramides

1.0

Cholesteryl sulfate

3.9

Unidentified

Table 5 Analysis of Commercial Paste-Type Facial Cleansers

Distribution of fatty acid (wt%)

Table 5 Analysis of Commercial Paste-Type Facial Cleansers

Distribution of fatty acid (wt%)

Sample

C12

C14

C16

C18

Sample A

5.9

16.8

1.4

6.4

Sample B

10.9

4.7

9.6

8.5

Sample C

0.0

15.0

6.9

4.0

Sample D

5.8

6.4

2.2

3.6

Sample E

4.9

13.3

3.5

5.8

Sample F

1.2

23.1

3.9

30.5

33.8

Figure 1 Effect of surfactant on the mo isture content of the skin. Forearms were washed every 20 minutes with 5 mL of surfactant solution (10%) and skin surface conductance was measured by surface hygrometer (Skicon 200;IBS Japan, at 25°C, 40 RH%, n = 6) as indicator of the moisture of the skin.
Figure 2 Effect of surfactants on the pH of human skin. Forearms were washed with 5 mL of surfactant solution (10%) and after that pH of the skin was measured every 20 minutes at 25°C, 40 RH%, n = 6.

stability, safety, and manageability or easiness of use, which are sometimes contradictory to fulfill all at once. Consumers' desire for a natural product requires not only that the ingredients used be natural but also that their appearance be natural-looking or transparent. Such requirements cause further difficulties for the formulation work [9].

Liquid-type skin cleansers have been developed mainly for facial use and diversified further to paste-type or gel-type formulations. Liquid-type body wash was developed first in Japan and spread widely to western markets with rapid growth even to replace significant share of soap bar market. This is among others because of their friendliness of use and added values as natural and mildness concepts.

Following are typical formulas of surfactant-type skin cleansers with their characteristics described:

Formula 1: Soap-Based Liquid Facial Cleanser (Excellent Lathering and Refreshing After-Feel)

Ingredients %

Lauric acid 2.5

Myristic acid 7.5

Palmitic acid 2.5

Lauric acid diethanolamide 2.0

Propylene glycol 8.0

Potassium hydroxide 3.6

Perfume q.s.

Preservative q.s.

Procedure: Add all the ingredients together and heat to dissolve with stirring. Cool down to room temperature.

* q.s., quantum satis (in sufficient amount).

Formula 2: Laurylethersulfate (LES)-Based Liquid Facial Cleanser (Compatible with Hard Water)

Ingredients %

Sodium polyoxyethylene(3)lauryl ether sulfate (30%) Sodium N-lauroylmethyltaurate (30%) Coconut acid diethanolamide Glycerin Sodium chloride Water Perfume Preservative

Procedure: Add all the ingredients together and heat with stirring. Cool down to room temperature.

* q.s., quantum satis (in sufficient amount).

to dissolve

Formula 3: Acylglutamate-Based Liquid Facial Cleanser Weakly Acidic, Leaves Skin Moist and Supple-Feeling

Ingredients

Triethanolamine N-cocoyl-L-glutamate (30%)

Cocoyl amide propyldimethyl glycine (30%)

1.3-butylene glycol

Sodium hydroxide

Water

Perfume

Preservative

Procedure: Add all the ingredients together and heat to dissolve with stirring. Cool down to room temperature.

* q.s., quantum satis (in sufficient amount).

Formula 4: Acylglycinate-Based Liquid Facial Cleanser (Excellent Lather and Refreshed After-Feeling Without Tightness)

Ingredients %

Potassium cocoyl glycinate (30%) 15.0

Potassium laurate 11.0

Potassium myristate 6.0

Glycerin 3.0

Ethylene glycol distearate 2.0

Hydroxypropylcellulose 0.5

Perfume q.s.

Preservative q.s.

Procedure: Add all the ingredients together and heat to dissolve with stirring. Cool down to room temperature.

* q.s., quantum satis (in sufficient amount).

Formula 5: Soap-Based Paste-Type Skin Cleanser [10] (Good Foaming and Cleansing Power)

Ingredients %

Stearic acid 10.0

Palmitic acid 11.0

Myristic acid 12.0

Lauric acid 2.0

Squalane 2.0

Potassium hydroxide 6.0

PEG1500 10.0

Glycerin 20.0

Glycerol monostearate 2.0

POE(30)glycerol monostearate ester 2.0 Water q.s.* to 100

Perfume q.s.

Preservative q.s.

Procedure: Heat fatty acids, emollient, humectants, and preservative together until melted and keep at 70°C (oil phase). Dissolve the alkali in the purified water and add this to the oil phase while stirring. Keep at 70°C until the neutralization reaction is completed. In Table 5, analytical results of the fatty acid compositions for the commercial soap-based paste-type facial cleanser are shown.

* q.s., quantum satis (in sufficient amount).

Formula 6: Acylglutamate-Based Paste-Type Facial Cleanser (Weakly Acidic, Moist and Supple After-Feeling)

Ingredients %

Sodium N-lauroyl-L-glutamate 35.0

Potassium laurate 5.0

Coconut acid diethanolamide 2.0

1.3-butylene glycol 10.0

Dipropylene glycol 20.0

Polyvinyl pyrolidone 0.5 Water q.s.* to 100

Perfume q.s.

Preservative q.s.

Procedure: Mix polyols and surfactants completely. Add other ingredients and water, then heat to dissolve. Cool to room temperature under reduced pressure with stirring.

* q.s., quantum satis (in sufficient amount).

Formula 7: Acylglycinate-Based Paste-Type Facial Cleanser (Neutral pH, Fresh After-Feeling)

Ingredients

%

Potassium cocoyl glycinate

32.0

Potassium myristate

1.5

Behenyl alcohol

0.5

Citric acid

2.5

1.3-butylene glycol

15.0

Glycerin

17.0

Ethylene glycol distearate

2.5

Water

q.s.* to 100

Perfume

q.s.

Preservative

q.ü.

Procedure: Mix polyols and surfactants completely. Add other ingredients and water then heat to dissolve. Cool to room temperature under reduced pressure with stirring.

Procedure: Mix polyols and surfactants completely. Add other ingredients and water then heat to dissolve. Cool to room temperature under reduced pressure with stirring.

* q.s., quantum satis (in sufficient amount).

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