3-Apr-2006

Cationic emulsifiers: an emerging trend in skin care

Abstract

Initially, the skin care market was dominated by soap based emulsions; triethanolamine and stearic acid were common in most skin care formulae. Nonionic emulsifiers increased the formulation opportunities by expanding the scope of compatible functional materials. In today’s market, cationic emulsifiers are broadening the range of aesthetics available to the formulator.

Figure 3. Moisturization study.

Initially, the skin care market was dominated by soap based emulsions; triethanolamine and stearic acid were common in most skin care formulae. Nonionic emulsifiers increased the formulation opportunities by expanding the scope of compatible functional materials. In today’s market, cationic emulsifiers are broadening the range of aesthetics available to the formulator.

The use of cationic emulsifiers is not new. In fact, the application area first seen in the market was skin care for babies. Mennen marketed this line under the trade name Baby Magic™ using two cationic emulsifiers (1). S.C. Johnson & Son launched the second cationic emulsifier based product, Curel®. The success of this product is due to the unique sensory profile that cationic moieties offer. Cationic emulsions give a smooth powdery after-feel that allows high active loadings without sacrificing efficacy.

This paper will provide formulators with the information needed to help with the selection of the Goldschmidt Personal Care cationic emulsifier that is most suitable for their particular application.

Product data

Characteristics

Cationic moieties have typically been associated with hair care for conditioning. In this application, they impart lubricity, antistatic properties and smoothness to hair fibers. These properties, plus excellent emulsifying properties, substantivity to the skin, renewable raw materials and a good cost/performance ratio, are increasing the interest in these well known ingredients for skin care applications.

As the use of cationic emulsifiers grows, there is increasing interest in expanding the sensory options available by modifying the cationic moiety in a formulation. In selecting a cationic emulsifier, these are some of points that should be considered:

  • Long chain or dialkyl quaternaries are milder on the skin than shorter chain monoalkyl analogues (2)
  • The hydrophilic/lipophilic ratio must be appropriate for the components in the formula
  • Long chain cationics are better emulsifiers
  • Cationics may be used alone or with co-emulsifiers
  • These emulsifiers are safe for use in skin care formulations

Excellent performance profiles recommend the use of three cationic materials as emulsifiers in skin care products: VARISOFT® TA 100, VARISOFT® PATC and TEGO® Care CE 40.

VARISOFT® TA 100 (INCI: distearyldimonium chloride) is a dialkyl quaternary, while VARISOFT® PATC (INCI: palmitamidopropyltrimonium chloride) and TEGO® Care CE 40 (INCI: cetearyl alcohol (and) palmitamidopropyltrimonium chloride) are amidoamine quaternaries. TEGO® Care CE 40 use level is higher than its pasty counterpart, but TEGO® Care CE 40 offers better handling properties in the laboratory and plant settings.

Sensory considerations – why to use cationic emulsifiers

The classic use of cationic products has been to improve conditioning properties of hair fiber. Cationic products may also be used as O/W emulsifiers for skin care. This functional transfer of some properties from traditional hair to skin care applications provides an innovative and economical platform to the formulator.

The consumer demographic shift over the next fifty years will lead to more than doubling of the 60+ age group, making this an attractive market for skin care product manufacturers. A major concern for this segment of the market is maintaining skin moisture. There are three strategies a formulator can follow to achieve this effect: the use of a skin barrier repair agent, humectants, and high lipophilic loadings. Often, moisturization is achieved via high lipophilic loading. The presence of a high oil phase, however, can impart an unpleasant oily or greasy and heavy skin feel. Cationic emulsifiers will mask these negative sensory properties, with the specific aesthetics determined by the choice of cationic emulsifier. In general, sensory properties for these emulsions are powdery, smooth and dry.

The formulation in Figure 1 was used to characterize the unique sensory profiles for distearyldimonium chloride and palmitamidopropyltrimonium chloride.

Formulating with cationic emulsifiers

Formulating with cationic emulsifiers is straightforward and similar to the techniques employed with the traditional nonionic emulsifiers. They can either be added to the water or the oil phase. Similar to other hydrophilic O/W emulsifiers, additional stabilization of the formulations is achieved by incorporating consistency enhancers such as stearyl alcohol, cetyl alcohol, glyceryl stearate or stearic acid. The addition of low levels of a monovalent salt, such as sodium chloride, may yield improved viscosity response and emulsion stabilization. Polyquaterniums will also help to improve long-term emulsion stability (4). Stabilizers in high amounts might create non-homogenous systems and could be visually unacceptable. Cationic emulsifiers are incompatible with anionic moieties, such as carbomers. These materials should be avoided or their use minimized.

Applications

Daily wear

The O/W cationic emulsion systems are used in facial, hand & body, baby, foot care and first aid products. The unique sensory effects of this type of system are readily perceived by consumers and make these products well suited for daily wear to protect and care for the skin.

Long lasting moisturization


A comparison of the moisturizing properties of nonionic versus cationic emulsifiers was conducted by an outside laboratory. The data in Figure 3 outlines the results from a moisturization study comparing TEGIN® Pellets (glyceryl stearate SE) against VARISOFT® TA 100 (distearyldimonium chloride). The moisture measurements were taken using a Corneometer over a 12 hour period using 11 panelists. The formulation in Figure 2 was used as the test formulation in this study.

Test lotions were applied to the back of the forearm twice a day. The amount applied was 2 mg/cm2. Corneometer readings were taken hourly. The results indicate that during the initial 8 hours of the study the TEGIN® Pellets (glyceryl stearate SE) showed increased performance. After more than 9 hours the cationic film showed superior performance. The rate of moisture loss is 2.6 times less with VARISOFT® TA 100 (distearyldimonium chloride). This result is most likely due to VARISOFT® TA 100’s ability to form a substantive durable film on the skin.

Guideline formulations


Several formulations have been made using cationic emulsifiers in the daily wear category. This includes the use of actives:

Modifying the aesthetics

Cationic emulsifiers are used as primary emulsifiers and add versatility as a secondary emulsifier in complex formulations . Even at low levels, consumers notice the sensory profile of cationic moieties. For example, using 1% of a cationic emulsifier in combination with a nonionic emulsifier can impart a powdery dry feel to the system.

Combining a cationic emulsifier with a silicone O/W emulsifier creates an emulsion with a powdery, velvety skin feel.

Sun care

With the increasing concern about sun induced skin damage, consumers are using sunscreens at the beach and throughout the year to protect their skin from premature ageing. Although an oily feel is acceptable for the beach, it is not acceptable for daily wear – the challenge to formulators is to develop high SPF formulae that protect the skin and wear well, but do not feel oily. Cationic emulsifiers can offer the formulator a means to achieve the aesthetics along with the additional benefit of water resistance.

Water resistance

Water resistance is an important factor in sun care formulae, especially those intended to be used at the pool or on the beach. Data from an in-vitro water resistance study conducted according to a protocol that is under preparation by the Latin sun screen producers group supports the benefits of cationic emulsifiers in this application.

The study evaluated the water resistance of three O/W emulsifiers and one W/O system: ceteareth-25, polyglyceryl-3 methylglucose distearate, distearyldimonium chloride and polyglyceryl-4 diisostearate / polyhydroxystearate / sebacate. The filter system used in all formulations was menthyl anthranilate (4%), ethylhexyl methoxycinnamate (5%) and ethylhexyl salicylate (4%). It is well known that O/W systems are less water resistant than W/O systems (see formulation numbers 1 and 2 in Figure 4). This is due primarily to O/W emulsions’ tendency to re-emulsify in the presence of water. But VARISOFT® TA 100 which is an O/W emulsifier does not show this tendency because of its strong substantivity to the skin.

The following measurements were made and the results are indicated in Figure 4:

The tests are performed featuring the following (5):

  • PMMA Hélioplates as substrate
  • Stirring method in a water-filled beaker
  • In-vitro testing by the Diffey Optometrics or the Kockott Sunscreen Tester

Under these test conditions cationic emulsions are 100% water resistant without film-forming additives, and are comparable to their W/O counterparts.

Conclusion

The use of cationic emulsifiers will continue to grow with the aging and performance driven consumer. Cationic emulsifiers offer the formulator a new tool in developing products which meet consumer demands. The unique properties of cationic emulsifiers enable the development of high lipophilic systems that offer enhanced consumer benefits without sacrificing aesthetics. Cationic emulsions lend a smooth powdery skin feel that nonionic and anionic emulsions do not. Applications which benefit from this technology include facial, hand and body, baby and foot care, sunscreens, and other systems where a non-oily, high lipophilic system is an advantage. Cationic emulsifiers offer these benefits:

  • • Excellent emulsification
  • • Combination with co-emulsifiers offer various possibilities to influence skin feel and absorption behavior
  • • Long-lasting skin moisturization
  • • Water resistance properties
  • • Renewable Resources
  • • Excellent cost/performance ratio

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