Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This review systematically summarizes the potential of algal active components in skin barrier repair, with a focus on skin barrier repair, moisturization and emollient properties. Through a review of published studies, it concludes that polysaccharides, phenols, carotenoids, and extracts from both large and small algae do indeed play effective roles in maintaining the skin barrier and restoring it after damage. This topic is in line with the current trend of "green cosmetics" and natural ingredient development, and has clear academic and application value. The article structure is clear, and the table organization is detailed.

To enhance the authority and accuracy of the article's content, I will present several questions and suggestions herein：

1. The article mentions that various algal compounds (such as polysaccharides, carotenoids, etc.) have the effect of promoting skin barrier repair. However, most of the studies have only reached the level of describing the phenomena. How do these compounds specifically regulate the expression of barrier proteins through which molecular pathways? Have there been any studies comparing the differences in mechanisms of the same compounds from different algal species?
2. The article cited some clinical studies, but did not conduct a systematic evaluation of the evidence level, sample size, and experimental design limitations of these studies. It is suggested that the authors add a section in the discussion to provide a critical analysis of the quality of the existing clinical research, in order to enhance the guidance of the review.
3. Algal extracts are mostly composed of multiple components. Currently, this review has not fully distinguished whether a single component plays a dominant role or if multiple components work synergistically. It is suggested that more research on the interactions and compatibility effects of the components be included. The analysis of component specificity and synergistic effects is lacking.
4. The author mentioned extraction technology and ecological sustainability in "Future Challenges", but did not delve deeply into key issues such as the stability of large-scale algae cultivation, the variability of component batches, and cost-benefit analysis - all of which are crucial for industrialization. It is suggested to add relevant content to enhance the reference value of the paper for the industry.
5. Table 1 is quite informative, but in some entries, the content in the "Type of study" and "Results" columns overlaps or is unclear. It is recommended to simplify and standardize the presentation style. For instance, some entries only state "In vitro" without specifying the specific cell model. The descriptions in references [53] and [54] are almost identical, but they are two separate citations. Detailed revisions are recommended.
6. On pages 4-5, the author states, "Spirulina (Arthrospira sp.)... although not classified as a microalga, it is regarded as a type of cyanobacteria." However, in the subsequent text and tables, it is still discussed together with microalgae without strictly differentiating them. Since the essence of Spirulina has been clearly stated, it is recommended to maintain this consistency of distinction throughout the entire text.
7. In the "3.8. Cosmetic patents" section, only the patents and their claimed effects were listed, but no evaluation or discussion was made regarding the experimental data or clinical evidence behind these patents. It is suggested to include some explanations to reasonably clarify the objectivity and significance of the patent information.

 

Author Response

Firstly, we would like to thank the reviewer for the valuable contribution which helped us to importantly improve the paper. We have tried to address all the concerns exposed and incorporated them into the current version of the manuscript. Please find here specific references to the text to facilitate their revision:

1. The article mentions that various algal compounds (such as polysaccharides, carotenoids, etc.) have the effect of promoting skin barrier repair. However, most of the studies have only reached the level of describing the phenomena. How do these compounds specifically regulate the expression of barrier proteins through which molecular pathways? Have there been any studies comparing the differences in mechanisms of the same compounds from different algal species?

A1. Some mechanisms are already explained; for example, for fucoidan and ulvan (please see lines 294-326), and phenols (lines 389-409). Other mechanisms have been added.

2. The article cited some clinical studies, but did not conduct a systematic evaluation of the evidence level, sample size, and experimental design limitations of these studies. It is suggested that the authors add a section in the discussion to provide a critical analysis of the quality of the existing clinical research, in order to enhance the guidance of the review.

A2. Thanks for the suggestion. We must say that this is not a systematic review. The aim is to highlight the potential use of algae compounds for an existing problem, such as the deterioration of the epidermal barrier and promote the use of these compounds in cosmetics.

3. Algal extracts are mostly composed of multiple components. Currently, this review has not fully distinguished whether a single component plays a dominant role or if multiple components work synergistically. It is suggested that more research on the interactions and compatibility effects of the components be included. The analysis of component specificity and synergistic effects is lacking.

A3. Reviewer is right. Thanks for the suggestions. We tried to emphasis this topic. Please, see lines 462 and 771.

4. The author mentioned extraction technology and ecological sustainability in "Future Challenges", but did not delve deeply into key issues such as the stability of large-scale algae cultivation, the variability of component batches, and cost-benefit analysis - all of which are crucial for industrialization. It is suggested to add relevant content to enhance the reference value of the paper for the industry.

A4. Despite this is not the aim of this review, information about large-scale cultivation and costs has been added.

5. Table 1 is quite informative, but in some entries, the content in the "Type of study" and "Results" columns overlaps or is unclear. It is recommended to simplify and standardize the presentation style. For instance, some entries only state "In vitro" without specifying the specific cell model. The descriptions in references [53] and [54] are almost identical, but they are two separate citations. Detailed revisions are recommended.

A5. Corrections on the references have been done.

6. On pages 4-5, the author states, "Spirulina (Arthrospira sp.)... although not classified as a microalga, it is regarded as a type of cyanobacteria." However, in the subsequent text and tables, it is still discussed together with microalgae without strictly differentiating them. Since the essence of Spirulina has been clearly stated, it is recommended to maintain this consistency of distinction throughout the entire text.

A6. According to specialists in the field (Dr. Leonel Pereira, University of Coimbra), since Arthrospira carries out oxygenic photosynthesis, the term microalgae can be used generally, especially when referring to its use in cosmetics or nutrition. In any case, we have tried to emphasize that it is a cyanobacteria.

7. In the "3.8. Cosmetic patents" section, only the patents and their claimed effects were listed, but no evaluation or discussion was made regarding the experimental data or clinical evidence behind these patents. It is suggested to include some explanations to reasonably clarify the objectivity and significance of the patent information.

A7. This section is just a sample of the most recent patents related to the topic.  Information about the content ca be found by typing the patent number into Google Patents.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

1. Lourdes Mourelle and coauthors have reported a review for revealing the potential use of macro and microalgae compounds in skin barrier repair which is excellent among similar review papers.

However, a minor revision is needed before acceptation.

 

1. the “macro and microalgae” of the title can be revised “algae” or “macro/micro-algae”.
2. It is suggested that the logic in the abstract section should be further improved. For example, the direct relationship between “compounds extracted from algae” and the “polysaccharides, phenols, carotenoids” in the abstract should be clarified.
3. the “skin barrier” of key words should be replaced by “skin barrier repair”.
4. I suggest that more figures should be supplemented from some key references.
5. The search data was just performed until June 2025. Therefore, I suggested some important references from June 2025 to Sep 2025 should be added.

Author Response

Firstly, we would like to thank the reviewer for the valuable contribution which helped us to importantly improve the paper. We have tried to address all the concerns exposed and incorporated them into the current version of the manuscript. Please find here specific references to the text to facilitate their revision:

1. the “macro and microalgae” of the title can be revised “algae” or “macro/micro-algae”.

A1. Thanks for the recommendation. I am not sure it we can change the title at this moment. I am going to ask the editor.

2. It is suggested that the logic in the abstract section should be further improved. For example, the direct relationship between “compounds extracted from algae” and the “polysaccharides, phenols, carotenoids” in the abstract should be clarified.

A2. Thanks for the recommendation. Information has been added.

3. the “skin barrier” of key words should be replaced by “skin barrier repair”.

A3. Done, thanks.

4. I suggest that more figures should be supplemented from some key references.

A4. This revision includes 33 pages, which does not leave room to add more figures. Sorry.

5. The search data was just performed until June 2025. Therefore, I suggested some important references from June 2025 to Sep 2025 should be added.

A5. References have been added. Thanks.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Mourelle et al. reported the potential use of macro and microalgae compounds in skin barrier repair. The following issues should be addressed.

1. The writing style of this manuscript is not a review paper. It is suggested to follow the writing style of a review paper published in the journal.
2. The skin barrier performances should be classified and discussed.
3. The mechanism of the various compounds for the skin barrier should be discussed.
4. Typical images in the references and the structure of the compounds should be provided.

 

Author Response

Firstly, we would like to thank the reviewer for the valuable contribution which helped us to importantly improve the paper. We have tried to address all the concerns exposed and incorporated them into the current version of the manuscript. Please find here specific references to the text to facilitate their revision:

1. The writing style of this manuscript is not a review paper. It is suggested to follow the writing style of a review paper published in the journal.

A1. Style has been revised according to MDPI rules. Thanks.

2. The skin barrier performances should be classified and discussed.

A2. Discussion about skin barrier functions and performances can be found in lines 33 to 76.

3. The mechanism of the various compounds for the skin barrier should be discussed.

A3. Thanks for the suggestion. Discussion has been enlarged.

4. Typical images in the references and the structure of the compounds should be provided.

A4. This revision includes 33 pages, which does not leave room to add more figures. And the aim is to highlight the potential use of algae compounds for an existing problem, such as the deterioration of the epidermal barrier and promote the use of these compounds in cosmetics, and not so much showing the structure of the bioactive compounds, an aspect that has already been addressed by the cited authors. My apologies for not being able to address the suggestion.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

The article starts with the structure and function of the skin barrier, introduces the causes and repair strategies of barrier damage, and naturally transitions to the potential of algal components. The structure is reasonable and the logic is smooth. Before publication, some issues need to be solved:
1、Some paragraphs are repetitive, such as the moisturizing mechanism of polysaccharides appearing repeatedly in different sub-chapters.
2、The discussion on the mechanism of action of algal components is scattered and lacks systematic summarization.
3、Section 4, "Future challenges and conclusions," is relatively general and does not propose specific research directions.
4、"Materials and Methods " and "Results and discussion" are not necessrary. It is not recommended for a review.
5、It is suggested to add a systematic summary of the safety evaluation of algal ingredients, especially their applicability to sensitive skin or specific populations.
6、Some references are not in a unified format, such as inconsistent abbreviation of journal names.

Author Response

Firstly, we would like to thank the reviewer for the valuable contribution which helped us to importantly improve the paper. We have tried to address all the concerns exposed and incorporated them into the current version of the manuscript. Please find here specific references to the text to facilitate their revision:

1、Some paragraphs are repetitive, such as the moisturizing mechanism of polysaccharides appearing repeatedly in different sub-chapters.

A1. Thanks for the suggestion. Writing has been improved.
2、The discussion on the mechanism of action of algal components is scattered and lacks systematic summarization.

A2. Thanks for the suggestion. Discussion has been improved.
3、Section 4, "Future challenges and conclusions," is relatively general and does not propose specific research directions.

A3. Thanks for the suggestion. Future challenges and conclusions have been improved.

4、"Materials and Methods " and "Results and discussion" are not necessrary. It is not recommended for a review.

A4. Thanks for the suggestion. In the web page of Applied Science, recommendations do not exclude these two sections.
5、It is suggested to add a systematic summary of the safety evaluation of algal ingredients, especially their applicability to sensitive skin or specific populations.

A5. Thanks for the suggestion. Safety evaluation of algal ingredients has been added.

6、Some references are not in a unified format, such as inconsistent abbreviation of journal names.

A6. References have been added using Zotero. The assistant editor will complete that at the end of the edition.

 

Author Response File: Author Response.pdf

Reviewer 5 Report

Comments and Suggestions for Authors

In this submission, the authors provide a comprehensive overview of the bioactive compounds derived from macro- and microalgae with potential applications in skin barrier repair. This review paper covers a wide range of metabolites (polysaccharides, carotenoids, phenols, lipids, etc.) and links them to dermatological and cosmetic applications. The topic is interesting and could attract wide readership. Therefore, I recommend its publication after the following issues are addressed.

1. The authors provide many examples to support their viewpoints. The representative ones could be highlighted using some figures.
2. The purpose of a review paper is to provide some scientific insights. Although many examples are provided, the insights still need to be more deeply discussed.
3. The manuscript reads as a compilation of studies, lacking deep analysis. For example, while many studies are cited on fucoidan or polysaccharides, there is little discussion on comparative efficacy or limitations of these findings.
4. While biological activities are described (e.g., hydration, reduction of TEWL, upregulation of filaggrin), the mechanistic pathways remain superficially treated. More discussions should be added on how these compounds influence skin barrier proteins, lipids, or microbiota.
5. The review mentions that algae extracts often act via multiple compounds, but does not analyze whether synergy (e.g., polysaccharides + lipids) has been experimentally demonstrated.
6. The article appears more heavily weighted toward macroalgae, with microalgae and cyanobacteria treated somewhat superficially. A deeper discussion of the potential of microalgae would be valuable.
7. The authors are recommended to cite relevant literatures such as Colloids Surf. B: Biointerfaces 2010, 76, 549. This literatures could serve as an examples of the application of polysacharrides and could potentially be used in the field of skin barrier repair.

Comments for author File: Comments.pdf

Author Response

Firstly, we would like to thank the reviewer for the valuable contribution which helped us to importantly improve the paper. We have tried to address all the concerns exposed and incorporated them into the current version of the manuscript. Please find here specific references to the text to facilitate their revision:

1. The authors provide many examples to support their viewpoints. The representative ones could be highlighted using some figures.

A1. This revision includes 33 pages, which does not leave room to add more figures. My apologies for not being able to address the suggestion.

2. The purpose of a review paper is to provide some scientific insights. Although many examples are provided, the insights still need to be more deeply discussed.

A2. More explanations have been added.

3. The manuscript reads as a compilation of studies, lacking deep analysis. For example, while many studies are cited on fucoidan or polysaccharides, there is little discussion on comparative efficacy or limitations of these findings.

A3. Thanks for the suggestion. The aim is to highlight the potential use of algae compounds for an existing problem, such as the deterioration of the epidermal barrier and promote the use of these compounds in cosmetics, more than discussing the quality or the limitations of the cited articles.

4. While biological activities are described (e.g., hydration, reduction of TEWL, upregulation of filaggrin), the mechanistic pathways remain superficially treated. More discussions should be added on how these compounds influence skin barrier proteins, lipids, or microbiota.

A4. Information about the mechanisms has been added.

5. The review mentions that algae extracts often act via multiple compounds, but does not analyze whether synergy (e.g., polysaccharides + lipids) has been experimentally demonstrated.

A5. Information has been added (see line 462, please).

6. The article appears more heavily weighted toward macroalgae, with microalgae and cyanobacteria treated somewhat superficially. A deeper discussion of the potential of microalgae would be valuable.

A6. There is a huge investigation about microalgae and cyanobacteria, but the research is not specially focus on skin barrier repair. In any case, some references have been added.

7. The authors are recommended to cite relevant literatures such as Colloids Surf. B: Biointerfaces 2010, 76, 549. This literatures could serve as an examples of the application of polysacharrides and could potentially be used in the field of skin barrier repair.

A7. Thanks for the recommendation, but this reference is related to chitosan, not algal polysaccharides, and while very interesting, it seems to be inconsistent with the purpose of this review.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript can be accepted now.

Reviewer 4 Report

Comments and Suggestions for Authors

The manuscript has been significantly improved and meets the criteria for publication.