On the Key Role of Polymeric Rheology Modifiers in Emulsion-Based Cosmetics

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Lines 48 ,49 - remove italics from words

line 114- define "synthetic" as you defined the others, not only by giving an example

Figure 2- ASE, HASE, HMIE, HEUR - are not defined in the text

Conclusion- remove the table

 

 

Author Response

Lines 48 ,49 - remove italics from words

Sorry for the mistake, now corrected.

 

line 114- define "synthetic" as you defined the others, not only by giving an example

Sorry for the mistake, now corrected.

 

Figure 2- ASE, HASE, HMIE, HEUR - are not defined in the text

Sorry for the mistake, definitions were now added in Figure legend.

 

Conclusion- remove the table

Thank you for the suggestion, the table was now removed.

Reviewer 2 Report

Comments and Suggestions for Authors

Peer Review Report

Manuscript Title: On the Key Role of Polymeric Rheology Modifiers in Emulsion-Based Cosmetics

General Assessment

This manuscript provides a mini-review on the role of polymeric rheology modifiers in emulsion-based cosmetics. It covers fundamental aspects such as classification, mechanisms, and application challenges of both synthetic and natural thickeners. The topic is highly relevant to the cosmetics industry, particularly in light of increasing sustainability concerns. However, the manuscript lacks scientific rigor, clarity, and accuracy in multiple areas, requiring substantial revision before being considered for publication. Below, I provide detailed revisions with major issues that need to be addressed.

Major Concerns and Required Revisions

Scientific Accuracy and Technical Depth

The scientific content lacks depth and often oversimplifies key concepts. Several technical aspects need substantial improvement.

1. Incomplete Discussion on Emulsions and Their Rheology

• The definition of emulsions (Lines 23-36) needs refinement. While the manuscript correctly states that emulsions are “thermodynamically unstable dispersions of two mutually insoluble liquids,” it fails to elaborate on the thermodynamic principles governing emulsion stability. A brief discussion on:
• Interfacial tension and Gibbs free energy considerations
• Role of surfactants and steric/electrostatic stabilization mechanisms
• Ostwald ripening and coalescence in emulsion stability
• The role of rheology modifiers in reducing phase separation and improving kinetic stability

would significantly enhance scientific accuracy.

• Rheology of emulsions: The manuscript does not explain how rheological properties affect product performance in terms of spreadability, sensory attributes, and long-term stability. Concepts like shear thinning, yield stress behavior, and viscoelasticity should be introduced.

1. Lack of Quantitative Data and Comparative Analysis

• The discussion on rheology modifiers (Lines 69-118) is too qualitative. The review should include:
• Comparative viscosity data for different rheology modifiers in standard formulations.
• Empirical studies on how different polymer concentrations affect emulsion stability (e.g., phase separation analysis over time).
• Comparisons of synthetic and natural thickeners in terms of molecular weight, rheological behavior, and stability.
• Example of missing data: The section on synthetic polymers (Lines 147-163) should discuss the molecular weight and functional group density of common thickeners like Carbomers, PEG derivatives, and polyacrylates and how these affect their performance.

1. Incorrect or Oversimplified Claims

Several claims need stronger justification:

• Claim (Lines 69-70): “Rheology modifiers can also help enhance the texture and feel of skin care products.”
• This is vague. The manuscript should discuss how specific polymeric structures impact sensory perception (e.g., viscosity, tackiness, spreadability).
• Claim (Lines 236-283): “Polyacrylates rightly fall under the name of microplastic particles.”
• Not all polyacrylates are solid-state microplastics. The authors must clarify which polymeric rheology modifiers meet the EU microplastic definition (solid, non-biodegradable, >5mm in size) and which do not.
• Claim (Lines 528-529): “The substitution of synthetic polymers with natural ones is extremely complicated due to high performance of oil-based polymers.”
• This is an overgeneralization. The authors should discuss specific challenges of replacing synthetic polymers, such as:
• Shear thinning and pseudoplastic behavior differences
• Electrostatic stability of natural vs. synthetic polymers
• Biodegradability vs. performance trade-offs

Adding references to case studies of successful natural polymer replacements (e.g., modified starches in personal care products) would strengthen the argument.

1. Weak Literature Review

• The manuscript lacks citations for key claims. While some references are included, the review does not critically engage with recent research. The following areas require more recent citations:
• Advances in synthetic rheology modifiers: What innovations exist to reduce environmental impact while maintaining performance?
• Emerging biopolymer alternatives: What research is being done on modified cellulose, bacterial cellulose, or functionalized polysaccharides?
• Regulatory developments: The review does not cite EU microplastics regulations, REACH directives, or sustainability trends in polymer design.

Structural and Logical Coherence

Certain sections lack coherence and flow.

• Repetition of Content:
• The introduction (Lines 20-42) contains redundant descriptions of emulsions that are later repeated in the main text.
• The discussion on synthetic polymers (Lines 147-200) revisits the same concepts multiple times without adding new insights.
• Weak Transitions Between Sections:
• The manuscript does not clearly explain how synthetic and natural thickeners compare in terms of rheological performance.
• The transition from rheology modifiers to microplastics (Lines 236-283) is abrupt and lacks a link to formulation science.

Improvements in Figures and Tables

• Figure 1 (Mechanisms of Rheology Modifiers):
• Needs better labeling to clarify which mechanisms apply to synthetic vs. natural polymers.
• Would benefit from examples of specific cosmetic formulations using each mechanism.
• Table 2 (Pros and Cons of Synthetic vs. Natural Polymers):
• Should include quantitative comparisons of viscosity range, stability time, and production costs.

Minor Issues

• Typos and Formatting:
• Line 12: “Being thermodynamically unstable one of the key part of their formulation is represented by stabilizers…” → Should read: “Being thermodynamically unstable, one key aspect of their formulation is the use of stabilizers…”
• Line 19: The keyword “thickeners” should be expanded to “rheology modifiers (thickeners, gelling agents, etc.)” for clarity.
• Line 140: “Substitution of oil-based polymers whit natural” → “Substitution of oil-based polymers with natural.”
• Reference Formatting:
• Some references are inconsistent in formatting. Ensure uniform citation style.

Final Decision

The manuscript requires major revisions before it can be considered for publication, as it lacks scientific depth, contains inaccuracies, and needs a stronger engagement with recent literature. Significant improvements in scientific rigor, structure, clarity, and technical details are necessary to elevate it to a publishable standard. Once these revisions are addressed, the paper will be significantly strengthened for publication in Cosmetics.

Comments on the Quality of English Language

Typos and Formatting issues were identified

Author Response

Major Concerns and Required Revisions

Scientific Accuracy and Technical Depth

The scientific content lacks depth and often oversimplifies key concepts. Several technical aspects need substantial improvement.

1. Incomplete Discussion on Emulsions and Their Rheology

• The definition of emulsions (Lines 23-36) needs refinement. While the manuscript correctly states that emulsions are “thermodynamically unstable dispersions of two mutually insoluble liquids,” it fails to elaborate on the thermodynamic principles governing emulsion stability. A brief discussion on:
• Interfacial tension and Gibbs free energy considerations
• Role of surfactants and steric/electrostatic stabilization mechanisms
• Ostwald ripening and coalescence in emulsion stability
• The role of rheology modifiers in reducing phase separation and improving kinetic stability

would significantly enhance scientific accuracy.

Following the suggestions from other reviewers we decided to remove the generic part on emulsions, known by audience, and focus our attention on rheology modifiers.

• Rheology of emulsions: The manuscript does not explain how rheological properties affect product performance in terms of spreadability, sensory attributes, and long-term stability. Concepts like shear thinning, yield stress behavior, and viscoelasticity should be introduced.

Thank you for the suggestion, details were added at the beginning of paragraph 2. In particular: “Rheology aims to study the deformation and flow characteristics of materials under the influence of external forces. In particular, the flow behavior of emulsions is a key property from the point of view of their applications and determines their ability to spread onto surfaces, sensory attributes and long-term stability. Emulsions belong to the family of Non-Netwonian fluids, fluids for which the viscosity, in particular, depends on time or shearing and cannot be named as “viscosity” but as “apparent viscosity”. Non-Newtonian fluids are classified as shear-thinning, shear-thickening, thixotropic and rheopectic fluids. In shear-thinning fluids, the apparent viscosity decreases with increasing shear stress; in shear-thickening fluids, in contrast, it increases. Shear-thinning viscosity is seen when asymmetrical, rigid particles orient themselves in a flow current, or when flexible, tangled polymers are deformed by a flow speed gradient. Shear-thickening behavior occurs occasionally; most frequently it is observed in certain emulsions once the critical volume concentration of some components has been reached or exceeded. In this case, the viscosity increases with increasing shear-rate and the product solidifies. An other category is represented by fluids with an initial yield stress that flow only above this value. The initial yield stress is interpreted as the point at which associated structures disintegrate. When the shear stress changes the fluids all adopt the corresponding speed gradient almost instantaneously. However, for some fluids a noticeable relaxation time is required. If the apparent viscosity at constant shear rate or constant shear stress decreases over time, the fluid is called thixotropic; if the apparent viscosity increases, the term used is rheopexy. An other key concept is represented by viscoelasticity. Ideal elastic materials are deformed under stress but return to their original shape and give up the energy absorbed after the applied force ceases.

In ideal viscous materials, the energy of the deformation is completely lost. Many materials are viscoelastic, that is, they exhibit both viscous and elastic behavior, which can be the cause of relaxation and retardation in technical processes and, depending on the application, may be usefill or damaging.”

 

1. Lack of Quantitative Data and Comparative Analysis

• The discussion on rheology modifiers (Lines 69-118) is too qualitative. The review should include:
• Comparative viscosity data for different rheology modifiers in standard formulations.
• Empirical studies on how different polymer concentrations affect emulsion stability (e.g., phase separation analysis over time).
• Comparisons of synthetic and natural thickeners in terms of molecular weight, rheological behavior, and stability.

Thank you for the suggestion, we now improved the quality of the manuscript in that part improving not only the definition of rheology modifier but also the most important concepts of rheology and the experimental apparatus used to obtain rheograms. Moreover studies on the effect of polymer concentration on emulsion stability were considered.

• Example of missing data: The section on synthetic polymers (Lines 147-163) should discuss the molecular weight and functional group density of common thickeners like Carbomers, PEG derivatives, and polyacrylates and how these affect their performance.

Thank you for the suggestion, details now added in sections of Carbomer, polyacrylates and acrylic polymers.

 

1. Incorrect or Oversimplified Claims

Several claims need stronger justification:

• Claim (Lines 69-70): “Rheology modifiers can also help enhance the texture and feel of skin care products.”
• This is vague. The manuscript should discuss how specific polymeric structures impact sensory perception (e.g., viscosity, tackiness, spreadability).

Thank you for the suggestion, we now added details on the roles of rheology modifiers together with information about rheology of emulsions and apparatus used to obtain rheograms.

• Claim (Lines 236-283): “Polyacrylates rightly fall under the name of microplastic particles.”
• Not all polyacrylates are solid-state microplastics. The authors must clarify which polymeric rheology modifiers meet the EU microplastic definition (solid, non-biodegradable, >5mm in size) and which do not.

Sorry for the mistake, now corrected. Of course it is a matter of physical state, biodegradability and size.

• Claim (Lines 528-529): “The substitution of synthetic polymers with natural ones is extremely complicated due to high performance of oil-based polymers.”
• This is an overgeneralization. The authors should discuss specific challenges of replacing synthetic polymers, such as:
• Shear thinning and pseudoplastic behavior differences
• Electrostatic stability of natural vs. synthetic polymers
• Biodegradability vs. performance trade-offs

Adding references to case studies of successful natural polymer replacements (e.g., modified starches in personal care products) would strengthen the argument.

Thank you for the suggestion, the conclusions were rewritten. In particular: “Rheological modifiers play a crucial role in cosmetics being responsible of the ability to spread onto surfaces (skin layer), sensory attributes and long-term stability. During the different production stages different viscosity are needed. Indeed, during processing (stirring an pumping) low viscosity is essential (100-1000 mPa s) to reduce costs and facilitate the entire manufacturing procedure. An other key part of their product life is represented by the application onto the skin and, also in this step, low viscosity are required (50-100 mPa s) to allow easy spread ability. On the contrary during transportation and storage the viscosity of the emulsion should be higher (10,000-100,000 mPa s) to prevent aggregation and then phase separation. It is so easy to state that shear thinning behavior is the most favorable one. The mechanisms behind the ability of rheology modifiers to lengthen the life time of emulsions are related to the formation of networks (physical or chemical) able to decrease the collisions between the particle of the disperse phase through the continuous phase. Many different synthetic and natural polymers are used in commercial product with correspondent advantages and disadvantages. In particular synthetic polymers can induce high stability, high mechanical performance and are easily produce in large volume at low costs while natural polymers lack in terms of costs, rheological performances if not modified and scale up. As current request trends push for greener, sustainable and non-oil-based raw ingredients, especially in the cosmetic field, the applicability of natural-grounded constituents in the rheology modifiers field is increasing. Indeed, despite the cons highlighted their biodegradability makes them ideal candidates in cosmetics. So, overcome the cons related to natural polymers is pivotal for the market success of the next generation of emulsion-base cosmetics.”

 

1. Weak Literature Review

• The manuscript lacks citations for key claims. While some references are included, the review does not critically engage with recent research. The following areas require more recent citations:
• Advances in synthetic rheology modifiers: What innovations exist to reduce environmental impact while maintaining performance?

• Thank you for the suggestion, examples with innovations on synthetic polymers were now added (paragraph3.1.3 ).

 

• Emerging biopolymer alternatives: What research is being done on modified cellulose, bacterial cellulose, or functionalized polysaccharides?

Thank you for the suggestion, examples with modified polymers were now added (paragraph 5).

 

• Regulatory developments: The review does not cite EU microplastics regulations, REACH directives, or sustainability trends in polymer design.

Thank you for the suggestion. We added a paragraph on that, in particular: “Indeed regulation (EU) 2023/2055 establishes the ban of synthetic polymer microparticles on their own or in mixtures in a concentration ≥ 0,01% by weight. The ban does not apply to the polymers that: (i) result from a natural polymerization process; (ii) are degradable; (iii) present a solubility higher than 2g/L; (iv) does not contain carbon atoms; (v) are permanently incorporated into a solid matrix; (vi) present physical properties permanently modified during intended end use so that the polymer no longer falls within the scope of the above classification.”

 

Structural and Logical Coherence

Certain sections lack coherence and flow.

• Repetition of Content:
• The introduction (Lines 20-42) contains redundant descriptions of emulsions that are later repeated in the main text.
• The discussion on synthetic polymers (Lines 147-200) revisits the same concepts multiple times without adding new insights.

Thank you for the suggestion, that parts were rewritten and repeated parts deleted.

 

• Weak Transitions Between Sections:
• The manuscript does not clearly explain how synthetic and natural thickeners compare in terms of rheological performance.
• The transition from rheology modifiers to microplastics (Lines 236-283) is abrupt and lacks a link to formulation science.

Thank you for the suggestion, that parts were rewritten and repeated parts deleted.

 

Improvements in Figures and Tables

• Figure 1 (Mechanisms of Rheology Modifiers):
• Needs better labeling to clarify which mechanisms apply to synthetic vs. natural polymers.
• Would benefit from examples of specific cosmetic formulations using each mechanism.

Thank you for the suggestion, we now added explanation and some references.

 

• Table 2 (Pros and Cons of Synthetic vs. Natural Polymers):
• Should include quantitative comparisons of viscosity range, stability time, and production costs.

Thank you for the suggestion, however considering also the suggestion of Reviewer 4 the table was removed. We now changed the conclusion section adding considerations on viscosity range, and costs.

 

Minor Issues

• Typos and Formatting:
• Line 12: “Being thermodynamically unstable one of the key part of their formulation is represented by stabilizers…” → Should read: “Being thermodynamically unstable, one key aspect of their formulation is the use of stabilizers…”

Sorry for the mistake, now corrected.

• Line 19: The keyword “thickeners” should be expanded to “rheology modifiers (thickeners, gelling agents, etc.)” for clarity.

Sorry for the mistake, now corrected.

• Line 140: “Substitution of oil-based polymers whit natural” → “Substitution of oil-based polymers with natural.”

Sorry for the mistake, now corrected.

• Reference Formatting:
• Some references are inconsistent in formatting. Ensure uniform citation style.

Sorry for the mistake, now corrected and all the citations uniformed.

 

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript does not present the need to conduct a review on polymeric rheology modifiers. Generally, it is poorly organized and not coherent. 
The manuscript lacks methodology. It is unclear how the articles were selected, assessed, and synthesized for the study's purpose. Inclusion and exclusion criteria are also not described. 

Comments on the Quality of English Language

It needs to be reviewed by a native English speaker.

Author Response

The manuscript does not present the need to conduct a review on polymeric rheology modifiers. Generally, it is poorly organized and not coherent. The manuscript lacks methodology. It is unclear how the articles were selected, assessed, and synthesized for the study's purpose. Inclusion and exclusion criteria are also not described.

 

We now improved the quality of the manuscript adding section related to the performances requested to the rheology modifiers, principles of rheology, experimental apparatus and discussion on future steps. In addition we discussed now the key performances requested and we added references on advances in synthetic rheology modifiers, emerging biopolymer alternatives and regulatory developments.

 

 

Reviewer 4 Report

Comments and Suggestions for Authors

Dear Authors, 

 

Please find below my suggestions: 

1. Line 10, use another term instead of parts (domain, area).
2. Some parts of the introduction are well-known theoretical aspects that were already discussed and I do not know if they should be highlighted in a review (emulsion definition, emulsions classification).
3. Line 66-67, the sentence should be rephrased
4. Do not use we, try to use it has been shown, or will be highlighted or other expression. (line 68)
5. In the last paragraph of the introduction more details should be included about what this review will outline.
6. Line 89-90 please rephrase
7. Line 92-94 a verb is missing, please read again the sentence
8. Figure 2, should be moved after the first paragraph where it was first mentioned.
9. Line 123 – with!
10. In Figure 2, the abbreviations should be explained
11. Some examples of rheological modifiers should be mentioned in the categories outlined in the introduction chapter (mentioned here and detailed in the following chapters of the article).
12. After 3.1. subchapter there are no indents!
13. Also, the text needs to be separated into paragraphs (in 3.1. subchapter there is a very long paragraph of almost one page)
14. Considering the introduction and the title I was not expecting anything regarding green cosmetics, also, in my opinion, that part with pollutants is not quite related to the topic of the article, or it should be transformed into a separate subsubchapter, or a very small paragraph, but as it is, I think it is a little bit too much!
15. In the case of marine polysaccharides, I was expecting some examples of concentrations of these compounds or related compounds as emulsifiers and the way their concentration influences the specific parameters evaluated in the case of emulsions. The same stands for galactomannans.
16. During the reading of the manuscript, I was expecting some rheograms or some mentions about the apparatus used to test the viscosity.
17. Line 528 (with)
18. Also, as a conclusion in some parts the line between the polymeric rheology modifies and the emulsion-cosmetics is lost, with no correlation being made at some points between these two. In some cases, the polymeric emulsifiers are treated separately and are not presented as parts of cosmetic emulsion, which should be the main topic of this article.

Comments on the Quality of English Language

I have compiled these two chapter in the above "document".

Author Response

Please find below my suggestions: 

1. Line 10, use another term instead of parts (domain, area).

Thank you for the suggestion, now corrected.

 

2. Some parts of the introduction are well-known theoretical aspects that were already discussed and I do not know if they should be highlighted in a review (emulsion definition, emulsions classification).

Thank you for the suggestion, some generic parts were deleted.

 

3. Line 66-67, the sentence should be rephrased

Sorry for the mistake, the sentence was now rewritten.

 

4. Do not use we, try to use it has been shown, or will be highlighted or other expression. (line 68)

Sorry for the mistake, now corrected.

 

5. In the last paragraph of the introduction more details should be included about what this review will outline.

Thank you for the suggestion. Additional sentences were added at the end of Introduction section. In particular: “From a formulation perspective key role in emulsions is played not only by emulsifiers, fundamental to decrease interfacial tension and stabilize the systems, but also by other ingredients. This review is focused on one of them that represents so a key ingredient of emulsion-based cosmetics: rheology modifiers, commonly referred as thickeners. They are incorporated in emulsion-based formulations to provide suspension control, reduce phase separation, and prevent syneresis. Moreover they can also help to enhance the texture and feel of skin care products. Aspects related to their choice will be discussed together with the new trends and challenges behind their use in cosmetics.”

 

6. Line 89-90 please rephrase

Sorry for the mistake, the sentence was now rewritten.

 

7. Line 92-94 a verb is missing, please read again the sentence

Sorry for the mistake, now corrected.

 

8. Figure 2, should be moved after the first paragraph where it was first mentioned.

Thank you for the suggestion, the figure was now moved.

 

9. Line 123 – with!

Sorry for the mistake, now corrected.

 

10. In Figure 2, the abbreviations should be explained

Sorry for the mistake, now the acronyms were added in the legend.

 

11. Some examples of rheological modifiers should be mentioned in the categories outlined in the introduction chapter (mentioned here and detailed in the following chapters of the article).

Thank you for the suggestion, some examples were added: “Their nature can be inorganic or organic. Clays, fumed silica, or Al stearate belong to the first category while polysaccharide, cellulose or acrylic polymers to the second one.”

 

12. After 3.1. subchapter there are no indents!

Sorry for the mistake, now corrected.

 

13. Also, the text needs to be separated into paragraphs (in 3.1. subchapter there is a very long paragraph of almost one page)

Thank you for the suggestion, we added three subparagraphs.

 

14. Considering the introduction and the title I was not expecting anything regarding green cosmetics, also, in my opinion, that part with pollutants is not quite related to the topic of the article, or it should be transformed into a separate subsubchapter, or a very small paragraph, but as it is, I think it is a little bit too much!

Following the suggestion on point 13 we added three subparagraphs and one on “considerations on synthetic polymers”.

 

15. In the case of marine polysaccharides, I was expecting some examples of concentrations of these compounds or related compounds as emulsifiers and the way their concentration influences the specific parameters evaluated in the case of emulsions. The same stands for galactomannans.

Thank you for the suggestion, examples with carrageenan, alginate, agar, galactomannans and pectin were added.

 

16. During the reading of the manuscript, I was expecting some rheograms or some mentions about the apparatus used to test the viscosity.

Thank you for the suggestion. We now added a paragraph on apparatus used to test the viscosity in emulsions. In particular: “Rheological properties are plotted using rheograms obtained using experimental apparatus [39, 40]. A variety of different viscometers and measuring techniques is now available to measure rheological properties. An assortment of norms have been agreed upon in different fields to indicate the rheology of fluid formulations in connection with parameters relevant to the application. Viscosity measurements are only reliable if the flow measured is laminar and so viscometers are designed to take this requirement into account. These flow conditions are favored by high viscosity and low shear rate. In most measuring systems, the flow nevertheless becomes turbulent at high shear rates, a fact that should be considered. Different methods can be used:

- capillary viscometers: flow through a cylindrical tube caused either by application of gas pressure or by hydrostatic pressure from the fluid column;

- rotation viscometers: the liquid is sheared between two surfaces on the stator-rotor principle using coaxial cylinders, cone and plate, or a disk and plate. Normally the rotation rate is controlled and the torsional moment measured. However, there are also rheometers in which the applied force is controlled, which are used to determine initial yield stress;

- falling ball viscosimeter: correlates the speed of motion of a ball through a fluid with its viscosity;

- bubble viscometer: correlates the speed of motion of a bubble through a fluid with its viscosity;

- efflux viscometer: measures the viscosity using the time taken for fluid to flow through a hole;

- forced oscillatory shearing: dynamic techniques that, using vibrations, permit the simultaneous investigation of both the dynamic viscous behavior and the elastic properties of fluid systems.”

 

17. Line 528 (with)

Sorry for the mistake, now corrected.

 

18. Also, as a conclusion in some parts the line between the polymeric rheology modifies and the emulsion-cosmetics is lost, with no correlation being made at some points between these two. In some cases, the polymeric emulsifiers are treated separately and are not presented as parts of cosmetic emulsion, which should be the main topic of this article.

Thank you for the suggestion, the conclusions were rewritten. In particular: “Rheological modifiers play a crucial role in cosmetics being responsible of the ability to spread onto surfaces (skin layer), sensory attributes and long-term stability. During the different production stages different viscosity are needed. Indeed, during processing (stirring an pumping) low viscosity is essential (100-1000 mPa s) to reduce costs and facilitate the entire manufacturing procedure. An other key part of their product life is represented by the application onto the skin and, also in this step, low viscosity are required (50-100 mPa s) to allow easy spread ability. On the contrary during transportation and storage the viscosity of the emulsion should be higher (10,000-100,000 mPa s) to prevent aggregation and then phase separation. It is so easy to state that shear thinning behavior is the most favorable one. The mechanisms behind the ability of rheology modifiers to lengthen the life time of emulsions are related to the formation of networks (physical or chemical) able to decrease the collisions between the particle of the disperse phase through the continuous phase. Many different synthetic and natural polymers are used in commercial product with correspondent advantages and disadvantages. In particular synthetic polymers can induce high stability, high mechanical performance and are easily produce in large volume at low costs while natural polymers lack in terms of costs, rheological performances if not modified and scale up. As current request trends push for greener, sustainable and non-oil-based raw ingredients, especially in the cosmetic field, the applicability of natural-grounded constituents in the rheology modifiers field is increasing. Indeed, despite the cons highlighted their biodegradability makes them ideal candidates in cosmetics. So, overcome the cons related to natural polymers is pivotal for the market success of the next generation of emulsion-base cosmetics.”

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have thoroughly addressed the major concerns raised in the previous review. The revised manuscript shows significant improvement in technical depth, clarity, and organization. Minor typographical and formatting issues remain, but these can be easily corrected during the final editing stage. I recommend acceptance of the manuscript pending minor revisions for typos and consistency.

Comments on the Quality of English Language

Minor typographical and formatting issues remain, but these can be easily corrected during the final editing stage.

Author Response

 

The authors have thoroughly addressed the major concerns raised in the previous review. The revised manuscript shows significant improvement in technical depth, clarity, and organization. Minor typographical and formatting issues remain, but these can be easily corrected during the final editing stage. I recommend acceptance of the manuscript pending minor revisions for typos and consistency.

Thank you very much for the comments that improved the quality of this work.

 

Reviewer 3 Report

Comments and Suggestions for Authors

The paper did not describe method of identifying and selecting article/sources used in the review. 

Comments on the Quality of English Language

None.

Author Response

 

The paper did not describe method of identifying and selecting article/sources used in the review. 

In this review we focused our attention on a key ingredient of emulsion-based cosmetics: rheology modifiers. They are incorporated in formulations to provide suspension control, reduce phase separation and prevent syneresis. Here we compared commonly used synthetic rheology modifiers with natural ones underlining the pros and cons of both of them. The examples considered are not the entire list of possibilities but discussed to help the discussion.

Reviewer 4 Report

Comments and Suggestions for Authors

Dear Authors,

 

I was expecting the lines where alterations were made to follow more easily the new information, but that was not the case. The article improved, still some minor revisions need to be done before accepting the manuscript:

1. Some words are misspelled: line 92, an other, instead of another (line 98).
2. Line 224 , the expression by the way should be replaced
3. Line 359-360, the sentence needs to be rephrased.
4. Line 402 - co-workers?
5. Line 529-530 - it is not clear what was study in that article. Also, check the font type and size.
6. G’ > G”  need to be explained before using them in the text.
7. The last sentence of the conclusion needs to be rephrased. 
8. The references need to align to the MDPI format.

Regards,

Comments on the Quality of English Language

These comments were introduced previously in the comments and suggestions for authors.

Author Response

 

I was expecting the lines where alterations were made to follow more easily the new information, but that was not the case. The article improved, still some minor revisions need to be done before accepting the manuscript:

1. Some words are misspelled: line 92, an other, instead of another (line 98).

Sorry for the mistake, now corrected.

 

2. Line 224, the expression by the way should be replaced.

Sorry for the mistake, now corrected.

 

3. Line 359-360, the sentence needs to be rephrased.

Sorry for the mistake, now corrected.

 

4. Line 402 - co-workers?

Sorry for the mistake, now corrected.

 

5. Line 529-530 - it is not clear what was study in that article. Also, check the font type and size.

Sorry for the mistake, detailed explanation was now added.

 

6. G’ > G” need to be explained before using them in the text.

Thank you for the suggestion, explanation now added.

 

7. The last sentence of the conclusion needs to be rephrased. 

Thank you for the suggestion. The last paragraph of conclusions was rephrased: “Indeed, despite the disadvantages already highlighted, the biodegradability associated to natural products makes them ideal candidates in cosmetics. So, the solution of the problems related to their production is pivotal for the market success of natural-based formulated products.”

 

8. The references need to align to the MDPI format.

Sorry for the mistakes, now corrected.