Thermal Spring Waters as Cosmeceuticals: An Update

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The article provides a comprehensive update on the use of thermal waters as cosmeceutical ingredients, both from the perspective of minerals and microbiological derivatives (hydrobiome). Numerous examples are provided of waters (e.g., Avène, Blue Lagoon, Dead Sea, Chaves, Vichy) and related formulations (sprays, gels, creams) that have demonstrated anti-inflammatory, hydrating, or protective effects in in vitro, ex vivo, and clinical studies, such as the reduction of post-chemical peel erythema with Avène (pages 5-6) or the improvement of hydration and skin barrier function with Jonzac or Crò (page 4).
A strong point is the inclusion of data on postbiotic and paraprobiotic ingredients (e.g., Aquaphilus dolomiae from Avène, Vitreoscilla filiformis from La Roche-Posay, table on page 8), which represent a recent and interesting trend in the field.
However, the text is very dense and at times repetitive, with lists of studies that risk making it difficult to read. Some sections (for example, the explanation of the definitions of pre/pro/postbiotics on page 7) could be made more concise. A critical discussion of the limitations of the cited studies (such as the lack of independent clinical trials or the potential commercial interests of the companies involved) is missing.
In the management of skin pigmentation alterations, in addition to topical and cosmeceutical treatments based on thermal waters [references already present], physical approaches such as the Q-Switched Nd:YAG laser have also been explored, which is particularly effective in Asian subjects (Q-Switched Nd:YAG Laser to Manage Hyperpigmentation in Asians: A Multicenter Study. Cosmetics 2023, 10, 44. https:// doi.org/10.3390/cosmetics10020044)
In summary, the article is well-researched, full of practical examples, and up-to-date, but could be improved by streamlining the narrative and introducing greater critical thinking about the available data.

Author Response

Thank you very much for all your comments, all your concerns and suggestions have been included in the current version of the manuscript.

• Critical discussion has been improved.
• Reference (https:// doi.org/10.3390/cosmetics10020044) has not been added as is not related to TSW.
  
  

Reviewer 2 Report

Comments and Suggestions for Authors

This is a timely and well-structured review on thermal spring water (TSW) and hydrobiome-derived ingredients in dermocosmetics/cosmeceuticals. The topic is relevant and the manuscript is generally clear and informative. Only minor revisions are needed to improve clarity, consistency, and interpretability.

1. If feasible, please consider tabulating the controlled clinical studies by disease indication. A concise table summarizing condition (e.g., AD/psoriasis/acne/rosacea/sensitive skin), study design (RCT/controlled trial), sample size, intervention, comparator, primary endpoint(s), duration/follow-up, and main findings would substantially improve readability and allow readers to quickly gauge the clinical evidence base.
2. The database/keyword description is helpful, but please provide at least: language restrictions (if any), basic inclusion/exclusion criteria, and whether screening was performed by one or more reviewers.
3. Ensure consistent abbreviations (e.g., avoid TWS/TSW inconsistency).
4. Fix line-break hyphenation issues in text.

 

Author Response

Thank you very much for all your comments, all your concerns and suggestions have been included in the current version of the manuscript.

Q1. If feasible, please consider tabulating the controlled clinical studies by disease indication. A concise table summarizing condition (e.g., AD/psoriasis/acne/rosacea/sensitive skin), study design (RCT/controlled trial), sample size, intervention, comparator, primary endpoint(s), duration/follow-up, and main findings would substantially improve readability and allow readers to quickly gauge the clinical evidence base.

A1. This information is provided in the text related to Results and Discussion.

Q2. The database/keyword description is helpful, but please provide at least: language restrictions (if any), basic inclusion/exclusion criteria, and whether screening was performed by one or more reviewers.

A2. Inclusion/exclusion criteria have been added.

Q3. Ensure consistent abbreviations (e.g., avoid TWS/TSW inconsistency).

A3. Abbreviations have been unified.

Q4. Fix line-break hyphenation issues in text.

A4. Line-break hyphenation in text has been improved.

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors The review presents a broad search on different platforms and in recent years backwards. Provides extensive information on the topic, being useful for searches.

Author Response

No comments.

Reviewer 4 Report

Comments and Suggestions for Authors

Thank you for writing a review that addresses a current and relevant topic. Overall, it is very well documented. The narrative is generally clear, but there are several points that could improve scientific rigor, structure and readability, particularly with regard to transparency of methodology, critical evaluation of evidence and language/formatting. Below are some suggestions.

Main comments

Line 61: In the introduction, the statement that the term “cosmeceutical” was coined by Albert Kligman is incorrect and should be amended. As explained in detail by Saint-Léger in the review article “Cosmeceuticals. Of men, science, and laws...” (International Journal of Cosmetic Science, 2012, 34, 396–401), the composite term “cosmeceuticals” was originally created by R.E. Reed in 1962, when he was president of the Society of Cosmetic Chemists, and only later popularized by A. Kligman. I recommend that the authors correct this historical attribution and cite Saint-Léger's article as the appropriate source.

Line 69-77: The introduction and conclusions mention the lack of specific regulations for cosmeceuticals and the Japanese model of quasi-drugs, but the regulatory section remains superficial. You could expand on this with a concise and more structured subsection comparing at least the EU, US, Japan, and optionally other important markets with regard to the status of cosmeceutical claims.

It is also essential to emphasize more strongly that, despite strong marketing claims, the current regulatory status is usually that of a “cosmetic product.”

Line 83: The Materials and Methods section lists the databases and search terms, but does not provide details on: inclusion/exclusion criteria, types of studies included or any selection processes. I suggest expanding this section to include the types of studies involved (clinical, observational, in vitro, ex vivo, patents) and the main inclusion/exclusion criteria.

Line 92, 408, 540: The main sections (TSW as active ingredients, hydrobiome derivatives, patents) mainly summarize the positive results and rarely discuss limitations or potential conflicts of interest (e.g., industry-sponsored studies by major brands). I recommend that for each major TSW (Avène, Blue Lagoon, Chaves, Comano, Cró, Dead Sea, Jonzac, La Roche-Posay, Uriage, Vichy, etc.), to add brief critical comments on the study design (open vs. randomized, sample size, choice of control), duration, and clinical relevance of the results (e.g., short-term reduction in TEWL vs. long-term control of the disease) and brand sponsorship or involvement where this may influence the results.

Line 92: The manuscript sometimes mixes evidence from balneotherapy/baths and topical dermocosmetic products in the same narrative. At the beginning of section 3, clearly distinguish between studies on balneotherapy/immersion and topical products (sprays, gels, creams, serums, etc.). In the tables and text, indicate whether the formulation is for bathing or whether it is a leave-on formulation.

Line 567-568: The manuscript declares “no conflicts of interest” and “no external funding,” while prominently featuring proprietary ingredients and branded clinical programs (Avène, La Roche-Posay, Vichy, Blue Lagoon, etc.). Authors should explicitly state whether they have any past or present collaborations, consultancies or funded projects with the companies mentioned. If there have been collaborations, these should be disclosed transparently, even if the specific review was not funded.

Minor comments

Lines 12: The abstract is balanced but very positive; a sentence on limitations and regulatory uncertainty would make it more critical and in line with the conclusions.

Lines 573: Abbreviations are listed at the end, but some are used in the text in slightly different forms (e.g., TSW vs. TWS, EPS vs. EPSs). Ensure that each abbreviation is defined when first used and used consistently (e.g., always “TSW” for “thermal spring water”).

Line 91, 408: Section 3 (TSW as active ingredients) is long and detailed, while section 4 (hydrobiome derivatives as active ingredients in cosmeceuticals) is relatively shorter, although the title and abstract highlight this emerging area. The repetitive clinical details in section 3 could be condensed slightly and section 4 could be expanded with a more systematic overview of each main hydrobiome-derived ingredient (A. dolomiae, V. filiformis, C. aponinum, etc.).

Line 552: The conclusion is concise but once again very positive. I suggest adding 2-3 sentences highlighting the need for independent comparative studies, as the studies reported are supported and self-referenced by the companies, which is a critical issue that typically characterizes this type of topic.

Comments on the Quality of English Language

The text is understandable but contains numerous minor grammatical errors (use of definite/indefinite articles, prepositions, verb tenses, word choice) and some typographical errors in lines 43, 52, etc. (e.g., “re-view,” “chronical diseases,” “im-prove,” “shooting effect” instead of “soothing effect,” “study performed to investigated”). A professional linguistic review is recommended to correct the aforementioned errors, as well as a careful review of the verb tenses (past vs. present) in the description of the individual studies.

Author Response

ANSWER

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 the revision:

Line 61: In the introduction, the statement that the term “cosmeceutical” was coined by Albert Kligman is incorrect and should be amended. As explained in detail by Saint-Léger in the review article “Cosmeceuticals. Of men, science, and laws...” (International Journal of Cosmetic Science, 2012, 34, 396–401), the composite term “cosmeceuticals” was originally created by R.E. Reed in 1962, when he was president of the Society of Cosmetic Chemists, and only later popularized by A. Kligman. I recommend that the authors correct this historical attribution and cite Saint-Léger's article as the appropriate source.

Answer: Explanation and reference have been added.

Line 69-77: The introduction and conclusions mention the lack of specific regulations for cosmeceuticals and the Japanese model of quasi-drugs, but the regulatory section remains superficial. You could expand on this with a concise and more structured subsection comparing at least the EU, US, Japan, and optionally other important markets with regard to the status of cosmeceutical claims.

It is also essential to emphasize more strongly that, despite strong marketing claims, the current regulatory status is usually that of a “cosmetic product.”

Answer: Information comparing regulations in EU, USA, Japan, and Korea has been added.

Line 83: The Materials and Methods section lists the databases and search terms, but does not provide details on: inclusion/exclusion criteria, types of studies included or any selection processes. I suggest expanding this section to include the types of studies involved (clinical, observational, in vitro, ex vivo, patents) and the main inclusion/exclusion criteria.

Answer: Inclusion/exclusion criteria have been added.

Line 92, 408, 540: The main sections (TSW as active ingredients, hydrobiome derivatives, patents) mainly summarize the positive results and rarely discuss limitations or potential conflicts of interest (e.g., industry-sponsored studies by major brands). I recommend that for each major TSW (Avène, Blue Lagoon, Chaves, Comano, Cró, Dead Sea, Jonzac, La Roche-Posay, Uriage, Vichy, etc.), to add brief critical comments on the study design (open vs. randomized, sample size, choice of control), duration, and clinical relevance of the results (e.g., short-term reduction in TEWL vs. long-term control of the disease) and brand sponsorship or involvement where this may influence the results.

Answer: Information has been added.

Line 92: The manuscript sometimes mixes evidence from balneotherapy/baths and topical dermocosmetic products in the same narrative. At the beginning of section 3, clearly distinguish between studies on balneotherapy/immersion and topical products (sprays, gels, creams, serums, etc.). In the tables and text, indicate whether the formulation is for bathing or whether it is a leave-on formulation.

Answer: Table 2 is specific for Cosmeceutical formulation. The allusions to the properties of natural water to the properties of natural water serve to support the reference studies.

Line 567-568: The manuscript declares “no conflicts of interest” and “no external funding,” while prominently featuring proprietary ingredients and branded clinical programs (Avène, La Roche-Posay, Vichy, Blue Lagoon, etc.). Authors should explicitly state whether they have any past or present collaborations, consultancies or funded projects with the companies mentioned. If there have been collaborations, these should be disclosed transparently, even if the specific review was not funded.

Answer: The information is correct.

Minor comments

Lines 12: The abstract is balanced but very positive; a sentence on limitations and regulatory uncertainty would make it more critical and in line with the conclusions.

Answer: Information has been added.

Lines 573: Abbreviations are listed at the end, but some are used in the text in slightly different forms (e.g., TSW vs. TWS, EPS vs. EPSs). Ensure that each abbreviation is defined when first used and used consistently (e.g., always “TSW” for “thermal spring water”).

Answer: Abbreviations have been clarified.

Line 91, 408: Section 3 (TSW as active ingredients) is long and detailed, while section 4 (hydrobiome derivatives as active ingredients in cosmeceuticals) is relatively shorter, although the title and abstract highlight this emerging area. The repetitive clinical details in section 3 could be condensed slightly and section 4 could be expanded with a more systematic overview of each main hydrobiome-derived ingredient (A. dolomiae, V. filiformis, C. aponinum, etc.).

Answer: there are not too much information about hydrobiome and cosmetics, but we considered to introduce this topic as is trendy.

Line 552: The conclusion is concise but once again very positive. I suggest adding 2-3 sentences highlighting the need for independent comparative studies, as the studies reported are supported and self-referenced by the companies, which is a critical issue that typically characterizes this type of topic.

Answer: Information has been added.

Comments on the Quality of English Language

The text is understandable but contains numerous minor grammatical errors (use of definite/indefinite articles, prepositions, verb tenses, word choice) and some typographical errors in lines 43, 52, etc. (e.g., “re-view,” “chronical diseases,” “im-prove,” “shooting effect” instead of “soothing effect,” “study performed to investigated”). A professional linguistic review is recommended to correct the aforementioned errors, as well as a careful review of the verb tenses (past vs. present) in the description of the individual studies.

Answer: The article has been carefully reviewed. Thanks.

Author Response File: Author Response.pdf

Reviewer 5 Report

Comments and Suggestions for Authors

This manuscript presents a comprehensive and timely review of the use of thermal spring waters (TSW) and their hydrobiome derivatives as active ingredients in cosmeceuticals. The topic is highly relevant given the increasing scientific and commercial interest in dermocosmetics, microbiome-derived actives, and postbiotic ingredients. The authors provide an extensive compilation of in vitro, ex vivo, and clinical studies, with particular strength in summarizing data related to well-known thermal waters (e.g., Avène, La Roche-Posay, Vichy, Blue Lagoon, Dead Sea). The manuscript demonstrates strong expertise and offers value as a reference source. However, to further strengthen its scientific rigor and practical relevance, several conceptual clarifications and structural refinements are recommended, particularly regarding regulatory positioning, safety considerations, and differentiation between medicinal and cosmetic contexts.

1. While the manuscript is rich in references and examples, it is largely descriptive. The authors are encouraged to strengthen the critical perspective by comparing the quality of evidence (in vitro vs. ex vivo vs. clinical, randomized vs. open-label studies), discussing limitations, such as small sample sizes, lack of controls, industry-sponsored studies, or heterogeneity in endpoints, highlighting inconsistencies or gaps in the literature (e.g., lack of standardized protocols for TSW evaluation).
2. Although unavoidable in this field, the manuscript relies heavily on data from a limited number of brands. The authors should acknowledge potential commercial bias more explicitly.
3. Present review focuses strongly on efficacy-oriented narratives, it insufficiently addresses safety assessment, toxicological complexity, and chemical variability, which are critical for translating thermal waters into compliant cosmetic ingredients. Addressing these points will significantly enhance the manuscript’s scientific depth and practical value. The manuscript discusses beneficial effects of TSW largely from a biological and clinical perspective, but systematic safety evaluation is underrepresented. While hydrobiome-derived components are mentioned, the manuscript lacks a chemically grounded discussion of NOM fractions such as humic acids (HA) and fulvic acids (FA), which are increasingly recognized as bioactive contributors in certain thermal waters.Please see the paper of Milankovic et al. 2025, RSC Advances (DOI:10.1039/D5RA01252J)
4. The discussion on cosmeceuticals and regulatory status is relevant but somewhat superficial. While the term cosmeceutical is widely used in the literature, it has no legal status in most regulatory frameworks, including the EU. From a regulatory standpoint, products discussed in this review are cosmetics, and any claims, safety assessments, and substantiation strategies must comply with cosmetic legislation. The authors are encouraged to explicitly state that cosmeceuticals are legally cosmetics, not a hybrid category, clearly distinguish between: therapeutic/medical effects observed in balneology or dermatology, cosmetic effects permitted under cosmetic regulations (e.g., soothing, barrier support, appearance-related benefits), and avoid implicit blurring of boundaries between medicinal claims and cosmetic claims, especially when referring to clinical outcomes. This clarification would greatly improve conceptual precision and regulatory relevance.
5. The manuscript would benefit from careful English language editing (grammar, tense consistency, hyphenation, and spelling). While some sentences are overly long and could be simplified for clarity, repetitions (e.g., descriptions of hydration, TEWL reduction, anti-inflammatory effects) should be reduced.
6. Ensure consistent use of terms such as thermal spring water (TSW), thermal mineral water, and thermal water. Clarify early on the distinction between postbiotics and paraprobiotics, and maintain consistent usage throughout.

Comments on the Quality of English Language

The manuscript would benefit from careful English language editing (grammar, tense consistency, hyphenation, and spelling). While some sentences are overly long and could be simplified for clarity, repetitions (e.g., descriptions of hydration, TEWL reduction, anti-inflammatory effects) should be reduced.

Author Response

Answer

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 the revision:

1. While the manuscript is rich in references and examples, it is largely descriptive. The authors are encouraged to strengthen the critical perspective by comparing the quality of evidence (in vitro vs. ex vivo vs. clinical, randomized vs. open-label studies), discussing limitations, such as small sample sizes, lack of controls, industry-sponsored studies, or heterogeneity in endpoints, highlighting inconsistencies or gaps in the literature (e.g., lack of standardized protocols for TSW evaluation).

Answer: Critical analysis has been improved.

1. Although unavoidable in this field, the manuscript relies heavily on data from a limited number of brands. The authors should acknowledge potential commercial bias more explicitly.

Answer: This point has been addressed and specified in the lines 182-185.

1. Present review focuses strongly on efficacy-oriented narratives, it insufficiently addresses safety assessment, toxicological complexity, and chemical variability, which are critical for translating thermal waters into compliant cosmetic ingredients. Addressing these points will significantly enhance the manuscript’s scientific depth and practical value. The manuscript discusses beneficial effects of TSW largely from a biological and clinical perspective, but systematic safety evaluation is underrepresented. While hydrobiome-derived components are mentioned, the manuscript lacks a chemically grounded discussion of NOM fractions such as humic acids (HA) and fulvic acids (FA), which are increasingly recognized as bioactive contributors in certain thermal waters.Please see the paper of Milankovic et al. 2025, RSC Advances (DOI:10.1039/D5RA01252J)

Answer: Explanation about NOM fractions and safety evaluation was added. Reference regarding NOM has been added.

1. The discussion on cosmeceuticals and regulatory status is relevant but somewhat superficial. While the term cosmeceutical is widely used in the literature, it has no legal status in most regulatory frameworks, including the EU. From a regulatory standpoint, products discussed in this review are cosmetics, and any claims, safety assessments, and substantiation strategies must comply with cosmetic legislation. The authors are encouraged to explicitly state that cosmeceuticals are legally cosmetics, not a hybrid category, clearly distinguish between: therapeutic/medical effects observed in balneology or dermatology, cosmetic effects permitted under cosmetic regulations (e.g., soothing, barrier support, appearance-related benefits), and avoid implicit blurring of boundaries between medicinal claims and cosmetic claims, especially when referring to clinical outcomes. This clarification would greatly improve conceptual precision and regulatory relevance.

Answer: Information regarding legislation has been added in the Introduction section.

1. The manuscript would benefit from careful English language editing (grammar, tense consistency, hyphenation, and spelling). While some sentences are overly long and could be simplified for clarity, repetitions (e.g., descriptions of hydration, TEWL reduction, anti-inflammatory effects) should be reduced.

Answer: English language has been improved.

1. Ensure consistent use of terms such as thermal spring water (TSW), thermal mineral water, and thermal water. Clarify early on the distinction between postbiotics and paraprobiotics, and maintain consistent usage throughout.

Answer: Terms related to thermal spring water have been unified. Post and para-probiotics are carefully explained; please, see ISAPP association definitions an article from Cuevas-González et al., 2020.

Author Response File: Author Response.pdf

Round 2

Reviewer 5 Report

Comments and Suggestions for Authors

Well done! The authors, in accordance with the comments, have improved the manuscript, which in this form can be accepted for publication.

Comments on the Quality of English Language

The manuscript would benefit from careful English language editing (grammar, tense consistency, hyphenation, and spelling). While some sentences are overly long and could be simplified for clarity, repetitions (e.g., descriptions of hydration, TEWL reduction, anti-inflammatory effects) should be reduced.