Understanding CAPB from Its Structure: How Cocamidopropyl Betaine Improves Foam, Enhances Mildness, and Supports Thickening

1 Introduction

The “betaine” discussed in this article specifically refers to cocamidopropyl betaine, a widely used ingredient in daily chemical cleansing formulations. Its international abbreviation is CAPB, while in domestic supply channels it is also often abbreviated as CAB. This article focuses on betaine-type amphoteric surfactants commonly used in cleansing products such as shampoos, body washes, facial cleansers, and hand washes. It does not refer to glycine betaine, which is commonly discussed in the fields of food, nutrition, or moisturization.

The value of betaine in formulations comes from its distinctive molecular structure: one end is a hydrophobic fatty chain, while the other end is a zwitterionic hydrophilic head group carrying both positive and negative charges. It is this structure that enables it to participate in interfacial adsorption, mixed micelle formation, micelle growth, and surface adsorption, thereby improving foam, mildness, viscosity, formulation compatibility, and certain antistatic performance.

2 Molecular Structure: The Source of Betaine’s Function

2.1 Simplified Structural Formula of Betaine

Cocamidopropyl betaine can be understood using the following simplified structural formula:

R–C(=O)–NH–(CH₂)₃–N⁺(CH₃)₂–CH₂–COO⁻ 

Where:

① RCO–: an acyl chain derived from coconut fatty acids; R is usually a mixture of alkyl or alkenyl groups with different carbon-chain lengths;

② C(=O)–NH: an amide structure;

③ (CH₂)₃: a propyl spacer;

④ N⁺(CH₃)₂: a quaternary ammonium positive-charge center;

⑤ CH₂–COO⁻: a carboxylate negative-charge group.

This structure can be divided into two main parts:

One end is a long-chain fatty group with hydrophobicity, which tends to approach oils, sebum, the air interface, and other hydrophobic regions. The other end is a charged hydrophilic head group, which tends to remain in the aqueous phase and interact with other charged molecules or surfaces. Therefore, betaine has the basic ability of a surfactant to reduce interfacial tension, while also showing the good formulation compatibility typical of zwitterionic surfactants.

2.2 Relationship Between Structural Units and Formulation Performance

Structural unit	Structural characteristics	Main function
R fatty chain	Hydrophobic; derived from coconut fatty acid components	Participates in soil dispersion, interfacial adsorption, foaming, and foam stabilization
Amide group	Located between the hydrophobic chain and the hydrophilic head group	Affects molecular packing, foam texture, and system compatibility
Propyl spacer	Separates the hydrophobic chain from the hydrophilic head group	Improves molecular arrangement at interfaces and within micelles
Quaternary ammonium positive-charge center	A stable positive-charge structure within the molecule	Helps surface adsorption, antistatic performance, and mild conditioning
Carboxylate negative-charge group	Forms a zwitterionic structure together with the quaternary ammonium positive center	Improves formulation compatibility and reduces strong charge conflicts

Betaine differs from ordinary anionic surfactants and also from typical cationic surfactants. The same molecule contains both a quaternary ammonium positive-charge center and a carboxylate negative-charge group. In common personal-care cleansing formulations, it mainly exhibits zwitterionic characteristics.

3 Interfacial Adsorption: Why Can It Clean and Foam?

3.1 Hydrophobic Fatty Chains Help Disperse Oils and Soils

Sebum, oily dirt, dust, and cosmetic residues are not easily removed by water alone. Cleansing products work mainly because surfactants can reduce the interfacial tension at oil-water and solid-liquid interfaces, making soils easier to wet, detach, disperse, and rinse away.

The R fatty chain in the betaine molecule is hydrophobic and tends to approach oils, sebum, or the air interface, while the hydrophilic charged head group remains in water. When the molecules orient themselves at the interface, interfacial tension decreases and the difficulty of dispersing oil into water is reduced. Therefore, betaine provides certain wetting, dispersing, cleansing, and co-cleansing effects.

In many conventional shampoo, body wash, and hand wash formulations, betaine is often used as a co-surfactant. It is commonly combined with SLES, AES, AOS, amino acid surfactants, APG, and other surfactants to support cleansing, foam enhancement, and improved system mildness. In some mild or sulfate-free cleansing systems, betaine can also serve as one of the important cleansing and foaming components. Its specific role depends on the primary surfactant system and the use level.

3.2 Adsorption at the Air-Water Interface Improves Foam Quality

Foam is a dispersed system in which air is enclosed by liquid films. Surfactants can adsorb at the air-water interface, making foam easier to form and improving the stability of the foam film.

The hydrophobic fatty chain of betaine can approach the air-water interface, while the hydrophilic head group remains in the aqueous phase. This arrangement helps foam formation. When compounded with anionic surfactants, betaine can also improve the stability of foam films, making the foam finer, softer, and less prone to rapid collapse. The role of betaine in foaming is not only to increase foam volume, but more importantly to improve foam texture and foam stability.

4 Mixed Micelles: Why Can It Reduce Irritation?

4.1 Irritation Is Related to Free Surfactant Monomers

The irritation potential of a cleansing product depends not only on a specific raw material itself, but also on the state in which surfactants exist within the system. In aqueous solution, surfactants may exist as individual molecules or aggregate into micelles. The more readily free surfactant monomers interact with stratum corneum lipids, proteins, or the ocular mucosa, the higher the irritation risk usually is.

Anionic surfactants such as SLES, SLS, and AOS have strong cleansing and foaming power. However, when used alone, they may cause relatively noticeable irritation to the skin and eyes. After betaine is added, it can form mixed micelles with these anionic surfactants, changing the distribution state of surfactants in the system.

4.2 Zwitterionic Head Groups Promote Mixed Micelle Formation

The quaternary ammonium positive-charge center in the betaine molecule can interact with the negatively charged head groups of anionic surfactants. This reduces electrostatic repulsion among anionic head groups of the same type, making it easier for different surfactants to arrange together within micelles.

After mixed micelles are formed, the free monomer activity and direct interaction mode of strong anionic surfactants in the system change. Their interaction with the stratum corneum, proteins, and ocular mucosa may be reduced, thereby helping lower the irritation potential of the cleansing system. Mildness is not determined by betaine alone; it is also related to the total surfactant concentration, pH, contact time, oils and moisturizing components, impurity control, and the overall formulation design. Therefore, the mildness of betaine is not an absolute property that exists independently, but rather a synergistic effect that appears in suitable compounded systems.

5 Micelle Growth and the Salt Curve: Why Can It Support Thickening?

5.1 Betaine Is Not a Traditional Thickener

Betaine is often considered to have a thickening effect, but it is not a thickener in the traditional sense. Polymeric thickeners such as cellulose, xanthan gum, and carbomer mainly increase system viscosity through hydration, extension, and entanglement of polymer chains. The thickening performance of betaine mainly comes from changes in the structure of surfactant micelles.

In other words, betaine does not thicken a system by itself. Instead, through its combined action with the primary surfactant, electrolytes, and pH, it changes the micellar structure, which ultimately appears as an increase in viscosity.

5.2 Mixed Micelle Growth Leads to Increased Viscosity

In anionic surfactant systems, electrostatic repulsion exists among molecular head groups. Micelles are usually relatively small, and the system viscosity is limited. After betaine is added, its quaternary ammonium positive-charge center can interact with anionic surfactants, reducing part of the electrostatic repulsion among head groups and making mixed micelles easier to grow. Within an appropriate surfactant ratio and electrolyte range, electrolytes such as sodium chloride can further screen electrostatic repulsion among head groups, promoting the transformation of micelles from smaller structures into rod-like micelles, wormlike micelles, or entangled micelles.

When micelles become longer and form entanglements, the internal flow resistance of the system increases. At the macroscopic level, this appears as an increase in viscosity. This process can be summarized as:

Small micelles → Mixed micelles → Long micelles or wormlike micelles → Enhanced entanglement → Increased viscosity

5.3 The Salt Curve Determines Thickening Performance

In anionic surfactant systems involving betaine, the “salt curve” phenomenon is common. More salt is not always better; instead, there is an appropriate range.

Salt addition stage	Micelle state	Viscosity performance
Low salt level	Electrostatic repulsion remains strong, and micelles are relatively small	Low viscosity
Moderate salt level	Charges are moderately screened, and micelles grow and entangle	Viscosity increases
Near the peak	Micelles reach a relatively high degree of entanglement	Highest viscosity
Excessive salt level	Micelle structure becomes unbalanced, with possible turbidity or phase-separation tendency	Viscosity decreases

5.4 Key Factors Affecting Thickening Performance

Whether betaine can support thickening depends on whether the specific system forms a suitable micellar structure.

Influencing factor	Key evaluation point
Type of primary surfactant	SLES/AES systems are usually more responsive to salt thickening; some amino acid surfactant or APG systems may not show a strong response
Betaine use level	Too low a ratio may provide insufficient synergy; too high a ratio may deviate from the optimal micellar structure
Salt content carried by the raw material	Different commercial grades contain different salt levels, which affects the subsequent salt curve
Added salt level	The viscosity peak needs to be identified; excessive salt should not be added all at once
pH	Affects carboxyl-group protonation, intermolecular interactions, and micellar packing; at low pH, betaine may exhibit more cationic behavior
Fragrance, oils, preservatives	May insert into or disturb the micellar structure
Cationic polymers	May affect clarity, deposition, flocculation, and viscosity

Therefore, when evaluating whether betaine can thicken a system, one should not look only at the use level. It is necessary to consider the micellar structure formed jointly by betaine, the primary surfactant, electrolytes, pH, and other components.

6 Formulation Applications: Differences Across Surfactant Systems

6.1 Betaine’s Compatibility Comes from Its Zwitterionic Structure

The betaine molecule contains both a positive-charge center and a negative-charge group. In common cleansing systems, it shows good formulation compatibility. It does not behave only as a negatively charged species like strong anionic surfactants, nor does it interact as strongly with anionic surfactants as typical cationic surfactants do, which can lead to precipitation or turbidity. Therefore, betaine can form mixed micelles with anionic surfactants and can also work with nonionic surfactants to improve foam and mildness.

However, good compatibility does not mean it can be used stably in every system. Different primary surfactants, different pH values, different salt levels, and different conditioning components can all change the actual performance of betaine.

6.2 Application Considerations in Different Systems

Compounded system	Main performance	Key evaluation point
SLES/AES system	Reduces irritation potential, improves foam, and enhances salt-thickening response	Focus on the salt curve, clarity, and low-temperature stability
AOS system	Improves foam texture and reduces the harsh degreasing feel	Focus on irritation potential, skin feel, and viscosity changes
APG system	Improves mildness and foam structure	APG systems are not always suitable for simple salt thickening
Amino acid surfactant system	Improves foam and after-wash skin feel	Focus on pH, clarity, and viscosity-building method
Cationic polymer system	Affects hair deposition and combability	Focus on flocculation, turbidity, excessive deposition, and rinse residue

The role of betaine varies across different systems. When compounded with SLES/AES, it often shows obvious synergy in foam enhancement, irritation reduction, and salt thickening. When compounded with APG or amino acid surfactants, the improvement in mildness and foam may be more prominent, but the viscosity-building approach usually needs to be redesigned. When used together with cationic polymers, special attention should be paid to clarity, deposition, and rinse residue.

7 Surface Adsorption and Antistatic Effects

7.1 The Quaternary Ammonium Positive-Charge Center Helps Adsorption onto the Hair Surface

Hair can easily generate static electricity after washing, friction, and blow-drying. Damaged hair cuticles are rougher, and the hair surface shows more pronounced negative-charge characteristics, making flyaway hair, frizz, and increased combing resistance more likely. The betaine molecule contains a quaternary ammonium positive-charge center, and this structure helps the molecule adsorb onto negatively charged hair surfaces. At the same time, the long-chain fatty group can provide mild lubrication on the hair surface. Therefore, in shampoo systems, betaine can provide certain auxiliary antistatic effects and help improve combability.

7.2 The Antistatic Effect Is Auxiliary

The antistatic and conditioning effects of betaine are auxiliary and cannot replace dedicated conditioning ingredients. If the formulation goal is a lightweight, mild, low-residue cleansing experience, betaine can provide good synergy. If the formulation goal is obvious smoothness, repair, and frizz control, the formulation usually needs to be designed together with cationic guar gum, polyquaterniums, BTAC, CTAC, silicone emulsions, or oil components.

8 Antimicrobial-Related Effects: Structural Basis and Application Limitations

8.1 Long-Chain Hydrophobic Structure and Charged Head Group Provide a Basis for Interaction

Betaine has both a long-chain hydrophobic structure and a charged hydrophilic head group. Many quaternary ammonium compounds with antimicrobial activity typically rely on positive-charge structures to interact with microbial surfaces and then use hydrophobic chains to affect cell membrane integrity. Structurally, betaine has a similar basis for interaction, so in some systems it may contribute to a certain degree of microbial inhibition.

8.2 Betaine Should Not Be Equated with Preservatives or Disinfectants

Having a structural basis for microbial inhibition does not mean that betaine can serve a preservative or disinfectant function in ordinary personal-care products. The use level of betaine, contact time, formulation environment, and organic load in ordinary shampoos, body washes, facial cleansers, and hand washes may all affect its actual antimicrobial performance. Whether a product has antimicrobial or bactericidal effects must be confirmed through corresponding testing. Claims involving antibacterial, antimicrobial, disinfecting, or related effects must also comply with relevant regulatory requirements.

9 Selection and Verification: How to Determine Whether a Betaine Is Suitable for a Formulation

9.1 Raw Material Specifications Determine Baseline Performance

To determine whether a betaine is suitable for a formulation, key indicators in the certificate of analysis should be reviewed.

Evaluation item	Main significance
Active matter content	Affects use level, foam, cleansing, and formulation compatibility
Solids content	Affects cost calculation and the water-phase balance of the formulation
Sodium chloride content	Directly affects the salt-thickening curve and viscosity peak
pH	Affects charge state, clarity, and system stability
Color and odor	Affect transparent products, low-fragrance products, and final product quality
Free amine	Affects odor, irritation potential, and product stability
3-Dimethylaminopropylamine (DMAPA)	A residual amine impurity that requires attention in betaine production and quality control; related to odor, irritation potential, and sensitization risk
Amidoamine, commonly referring to cocamidopropyl dimethylamine	A synthesis-related intermediate and potential residual impurity of betaine; its residual level and irritation risk should be monitored in quality control
N-nitrosation risk	CAPB and related betaines contain structures that may participate in N-nitrosation reactions and may contain amine impurities; formulation design should avoid coexistence with N-nitrosating agents
Microbiological indicators	Affect raw material storage and finished-product preservation design
Low-temperature stability	Affects winter storage and transportation as well as the stability of transparent systems

Among these, DMAPA and amidoamine are impurities repeatedly emphasized in the safety evaluation of betaine. For high-quality betaine, it is important to look not only at the active matter content, but also at the control of by-products and impurities.

9.2 Formulation Suitability Must Be Confirmed Through Experiments

The application performance of betaine is highly dependent on the specific formulation. In actual development, its suitability should be evaluated through formulation experiments.

Test item	Evaluation purpose
Screening of primary surfactant/betaine ratio	Determines the balance among foam, mildness, and viscosity
Salt gradient experiment	Identifies the viscosity peak and safe salt-addition range
pH gradient experiment	Evaluates changes in viscosity, clarity, and stability
Fragrance compatibility test	Determines whether turbidity, viscosity loss, or precipitation occurs
High- and low-temperature stability testing	Evaluates whether phase separation, crystallization, or turbidity occurs under storage and transportation conditions
Compatibility test with cationic polymers	Evaluates deposition, combability, flocculation, and rinse residue
Foam and skin-feel testing	Evaluates foam texture and after-cleansing feel during actual use

9.3 Typical Advantages and Application Limitations

Typical advantage	Source
Improved foam	Oriented arrangement of the hydrophobic chain and hydrophilic head group at the air-water interface
Reduced irritation potential	Formation of mixed micelles with anionic surfactants
Auxiliary thickening	Growth and entanglement of mixed micelles under the action of electrolytes
Good formulation compatibility	Zwitterionic structure reduces strong charge conflicts
Auxiliary antistatic effect	The quaternary ammonium positive-charge center enhances adsorption onto negatively charged surfaces

Application limitation	Reason
Limited cleansing power when used alone	More suitable as a co-surfactant or formulation-modifying component
Thickening effect depends on the system	Affected by the primary surfactant, electrolytes, pH, and micellar structure
Excessive salt can reduce viscosity	After exceeding the optimal range for micelle growth, the structure becomes unbalanced
Cannot replace preservatives	A structural basis for microbial inhibition does not equal finished-product preservative capability
Cannot replace strong conditioning agents	Antistatic and conditioning effects are relatively auxiliary

10 Representative Chemicals Related to Betaine Structural Mechanisms and Personal-Care Cleansing Formulation Research

Table 1 Betaine and Compounded Surfactants

Category	CAS No.	Aladdin Cat. No.	Name	Specification or purity	Product features and applications
Betaine surfactant	61789-40-0	C665446	Cocamidopropyl Betaine	Actives content 28%–32% in water	A betaine-type amphoteric surfactant used for foam evaluation, mild cleansing systems, compounding with anionic surfactants, and salt-thickening experiments
Alkyl betaine structural reference	683-10-3	L196320	Lauryl Betaine	25%–29%	A representative alkyl betaine used for studies of zwitterionic head groups, chain-length effects, foam performance, and formulation compatibility
Long-chain sulfobetaine surfactant	2281-11-0	D105325	3-Sulfopropylhexadecyldimethylammonium Betaine	≥98%	A C16 long-chain sulfobetaine used for studies related to zwitterionic surfactants, chain-length effects, foam, and antistatic performance
Long-chain sulfobetaine surfactant	14933-09-6	M105324	3-Sulfopropyltetradecyldimethylammonium Betaine	≥98%	A C14 long-chain sulfobetaine used for studies of zwitterionic surfactant structures, mild membrane-protein solubilization, and micellar behavior
Zwitterionic non-detergent sulfobetaine	160788-56-7	N276111	NDSB-221, Zwitterionic Non-Detergent Sulfobetaine	≥97%	A zwitterionic sulfobetaine-structure product used for protein stabilization, solubility enhancement, and research on non-detergent zwitterionic systems
Short-chain sulfobetaine detergent	15178-76-4	S110923	Sulfobetaine 8	≥98%	A C8 sulfobetaine-type zwitterionic detergent used for micelle studies, chain-length effects, and membrane-related solubilization experiments
Short-chain sulfobetaine detergent	15163-36-7	S110924	Sulfobetaine 10	≥98%	A C10 sulfobetaine-type zwitterionic detergent used for protein solubilization, zwitterionic micelles, and chain-length comparison experiments
Short-chain sulfobetaine detergent	15163-36-7	S684499	Sulfobetaine 10	≥95%	A C10 sulfobetaine detergent used for protein solubilization, zwitterionic micelles, and comparison experiments across different specifications
Amine oxide co-surfactant	1643-20-5	N755731	N,N-Dimethyldodecylamine N-Oxide (DDAO)	BioReagent, ≥99%	An amine oxide co-surfactant used for foam stabilization, mixed micelle behavior, and mild cleansing formulation studies
Anionic surfactant irritation model	151-21-3	S432157	Sodium Dodecyl Sulfate (SDS)	Anhydrous, ACS, ≥99%	A strong anionic surfactant used for mixed micelles, irritation-control comparisons, foam, and surface-tension experiments
Anionic surfactant for compounding	9004-82-4	S196294	Sodium Polyoxyethylene Lauryl Ether Sulfate	≥25%	An anionic primary surfactant used for betaine compounding, salt-curve studies, foam stability, and personal-care cleansing system research
Anionic surfactant for compounding	68439-57-6	S304377	Sodium α-Olefin Sulfonate	≥92%	An olefin sulfonate surfactant used in model formulations for body washes and hand washes, as well as experiments on synergistic foaming with betaine
Mild anionic surfactant	137-16-6	N476195	Sodium N-Lauroylsarcosinate	UltraBio™, molecular biology grade, ultrapure, ≥99% (HPLC)	A mild sarcosinate surfactant used for mild facial cleansers, personal-care foam systems, and evaluation of betaine compounding
Nonionic synergistic surfactant	68515-73-1	T476404	Decyl Glucoside (APG)	Moligand™, 60% in H₂O	An alkyl glucoside nonionic surfactant used for mild cleansing systems, synergistic foaming with betaine, and formulation stability studies
Nonionic synergistic surfactant	110615-47-9	L196324	Dodecyl Glucoside	≥40%	A glucoside nonionic surfactant used for sulfate-free cleansing systems, foam texture, and formulation compatibility evaluation

Table 2 Chemicals Related to Micellar Thickening, Acid-Base Adjustment, and System Stability

Category	CAS No.	Aladdin Cat. No.	Name	Specification or purity	Product features and applications
Electrolyte thickening regulator	7647-14-5	S433743	Sodium Chloride	Anhydrous, ACS, ≥99%	Used for salt-curve experiments, micelle-growth studies, and viscosity adjustment in betaine/anionic surfactant systems
Buffer salt	6132-04-3	S116315	Sodium Citrate Dihydrate	Molecular biology grade, ≥99%	Used for buffering cleansing systems, stabilizing acidity/alkalinity, and studying betaine formulation stability
Acidity regulator	77-92-9	C755557	Citric Acid Anhydrous Powder	UltraBio™, anhydrous, ≥99.5% (T)	Used for acidity adjustment in betaine systems, buffer-system construction, and stability studies of transparent formulations
Acidity regulator	50-21-5	L108839	DL-Lactic Acid	AR, 85%–90%	Used for acidity adjustment in mild cleansing formulations, hair-care systems, and studies of the charge state of betaine
Alkalinity regulator	1310-73-2	S111501	Sodium Hydroxide	ACS, ≥97%	Used for neutralization, fine pH adjustment, and surfactant-system stability experiments in betaine formulations
Polymeric thickening stabilizer	9004-62-0	H434475	2-Hydroxyethyl Cellulose (HEC)	Average Mw ~380,000	A nonionic cellulose thickener used for viscosity building, suspension stability, and rheological comparison experiments in betaine cleansing systems
Polymeric thickening stabilizer	11138-66-2	G104873	Xanthan Gum	PharmPure™, USP	A polysaccharide thickening stabilizer used for viscosity, suspension stability, and polymer-thickening comparison studies in betaine systems

Table 3 Chemicals Related to Structural Origins, Conditioning/Antistatic Effects, and Quality Control

Category	CAS No.	Aladdin Cat. No.	Name	Specification or purity	Product features and applications
Synthetic intermediate and impurity control	68140-01-2	N304368	N-[3-(Dimethylamino)propyl]cocamide	Total amine value: 178–188 mg KOH/g	An amidoamine intermediate related to betaine synthesis, used for studies of structural origin, residue control, and irritation-related evaluation
Amine raw material and impurity control	109-55-7	D110909	3-Dimethylaminopropylamine (DMPDA)	≥99%	An amine raw material related to betaine synthesis and a residue-control target, used for impurity, odor, and irritation-related testing
Carboxymethylation-related raw material	79-11-8	C485697	Chloroacetic Acid (CAA)	≥99%	A carboxymethylation-related raw material used for studying the origin of the carboxylate structure and synthesis pathway of betaine
Carboxymethylation-related raw material	3926-62-3	S108371	Sodium Chloroacetate	AR, ≥98%	A salt related to the carboxymethylation reaction, used for studying the formation of the zwitterionic structure of betaine
Fatty-chain structural reference	143-07-7	L110736	Lauric Acid	GR, ≥99%	A representative C12 fatty acid used for studies of the hydrophobic-chain origin, chain-length effects, and foam performance of betaine
Cationic conditioning polymer	81859-24-7	P341830	Polyquaternium-10	Viscosity 300–500 mPa·s (2% aqueous solution, 25°C)	A cationic conditioning polymer used for studies of antistatic performance, wet combability, deposition behavior, and betaine compounding in shampoo systems
Cationic quaternary ammonium conditioning agent	112-02-7	H105309	Hexadecyltrimethylammonium Chloride (CTAC)	≥97%	A quaternary ammonium cationic surfactant used as a reference for antistatic effects, hair-surface adsorption, and the weak conditioning effect of betaine
Cationic quaternary ammonium conditioning agent	17301-53-0	N587655	N,N,N-Trimethyldocosan-1-aminium Chloride	≥80%	A long-chain quaternary ammonium conditioning agent used for hair conditioning, antistatic effects, and surface-adsorption comparison studies

Note: The above are representative Aladdin products related to scientific research and formulation studies. For more product specifications, grades, and COA information, please search by “product name/CAS/catalog number” on the Aladdin website.

References

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[2] Burnett C. L., Boyer I., Bergfeld W. F., Belsito D. V., Hill R. A., Klaassen C. D., Liebler D. C., Marks J. G. Jr., Shank R. C., Slaga T. J., Snyder P. W., Gill L. J., Heldreth B. Safety Assessment of Fatty Acid Amidopropyl Dimethylamines as Used in Cosmetics. International Journal of Toxicology. 2019;38(1_suppl). doi:10.1177/1091581819836089.

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[6] Yavrukova V. I., Radulova G. M., Danov K. D., Kralchevsky P. A., Xu H., Ung Y. W., Petkov J. T. Rheology of Mixed Solutions of Sulfonated Methyl Esters and Betaine in Relation to the Growth of Giant Micelles and Shampoo Applications. Advances in Colloid and Interface Science. 2020. doi:10.1016/j.cis.2019.102062.

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