ABSTRACT
Background and Aims
Remnants of laundry detergent ingredients are suspected to be in constant contact with the skin. Allergy sufferers need assurance that the chemicals in everyday products do not cause such disruption. The purpose of this study was to evaluate the effects and tolerability of common laundry detergents on the skin microbiome in individuals with atopic dermatitis.
Methods
Two laundry detergents for sensitive skin were tested on subjects with atopic dermatitis by having to wear detergent‐washed socks for 7 days. The bacterial population from volunteers’ skin swabs was determined and bacterial viability and biodiversity was evaluated before and after wearing the detergent‐washed socks. The tolerability and effect on atopic dermatitis was also evaluated.
Results
The results showed that the tested laundry detergents did not have a negative effect on bacterial viability or biodiversity on the skin after being exposed to the detergent‐washed socks for a week. The laundry detergents were rated as very good on the tolerability scale and no worsening of skin itch was reported with the use of either detergent.
Conclusion
The results of the study showed that both laundry detergents are skin and allergy friendly and do not alter the skin microbiome.
Keywords: allergy‐friendly detergents, atopic dermatitis, skin microbiome
1. Background
Atopic dermatitis (AD) is a chronic inflammatory skin disease with a high impact on patients' quality of life and the healthcare system [1]. The prevalence of AD is higher than 30% in some countries, yet the avoidable eliciting factors are still often used in everyday life [1]. Laundry detergents can contribute to allergic reactions due to the use of irritants like preservatives or fragrances that can disrupt the skin microbiome. Ingredients, such as microbial enzymes, are constantly in contact with the skin and can cause an impaired skin barrier, leading to allergic sensitization [2]. People with sensitive skin or allergies need assurance that the chemicals in everyday use products do not cause such disruptions and are safe for people's health and the skin microbiota.
The skin functions as a physical barrier against external harm and pathogens and can respond to external stimuli [3]. Millions of microorganisms (the skin microbiome) live on the skin and play important roles in protection against pathogens, skin homeostasis, immune responses, and metabolism [3]. The skin microbiome is crucial for our health and shifts in the microbiome flora can contribute to disease.
The skin microbiome plays a key role in immune responses by communicating with skin cells and is therefore essential in the pathogenesis of AD [4]. Atopic skin is characterized by a lack of microbial diversity and an overexpression of the pathogenic bacterium Staphylococcus aureus (S. aureus), which displaces non‐pathogenic microbes such as Staphylococcus epidermidis (S. epidermidis) [4]. Daily use of chemicals that could potentially disrupt the microbiome should be identified and avoided. The microbiota of textiles and the ones of domestic washing machines appear to originate predominantly from skin and the surrounding environment, being determined mainly by textile and appliance characteristics, handling, and use, as well as geo‐ and demographic factors [5].
ECARF (European Centre for Allergy Research Foundation), a non‐profit organization founded in 2003, aims to make life easier for allergy sufferers. The organization awards the “ECARF Seal of Quality” to products that have been evaluated as allergy‐friendly through scientific testing, including an evaluation of raw materials, composition, patient testing, and a functioning complaint management system. Although ECARF‐certified products have been scientifically tested and are expected to be skin compatible, individual reactions cannot be completely ruled out.
2. Questions Addressed
This study aimed to determine if allergy‐friendly‐certified laundry detergents are not only tolerable for individuals with AD but also if they do not alter the skin microbiome.
3. Experimental Design
3.1. Subject Testing
The two laundry detergents tested in this study, one liquid (Persil Sensitive Gel, manufactured by Henkel) and one powder form (Persil Megapearls Sensitive, manufactured by Henkel) were purchased in a common supermarket. Both products are currently marketed in that formulation throughout Europe. The study included 21 subjects (18 females and 3 males, average age 39.2 years) with AD and 20 subjects (16 females and 4 males) with AD, for testing of Persil Sensitive Gel and Persil Megapearls Sensitive, respectively. The subjects were selected according to the following inclusion criteria: oral and written consent form, ages 18–65, persons with AD; and the following exclusion criteria: non‐German speakers, individuals on immunosuppressive medications (such as systemic corticosteroids, cyclosporine), pregnancy lactation, and psychiatric diseases.
For this purpose, the test persons wore detergent‐washed socks over 7 days, under everyday conditions.
All subjects were informed about the study procedure and possible risks in a detailed discussion with the study physician. Written informed consent was obtained from all subjects. The studies for Persil Megapeals Sensitive (093‐W‐20) with the ethical approval number EA1/312/20, and the Persil Sensitive Gel (091‐W‐20) with the ethical approval number EA1/311/20), were approved by the Charité Ethics Committee.
3.2. Skin Microbiome
Skin swab samples were taken from subjects to test the effects on the skin microbiome. A sterile ring (diameter 35 mm) was used to delineate the test area (dorsal foot, near the toe area). On the defined area, 2.5 mL of 1 × PBS buffer/0.1% Tween20 was applied with a sterile syringe, and a skin swab was taken with a sterile pipette (15× each) in vertical and horizontal direction under equal pressure. The swab samples were collected on Day 0 (before wearing the detergent‐washed socks) and on Day 7 (1 week after wearing the detergent‐washed socks). The swabs were examined using microbiological methods.
For the determination of total aerobic mesophilic microorganisms, the aerobic plate count method on Tryptone Soya Agar was used. For the determination of bacterial count of Staphylococci, a mannitol salt agar was used. Each sample was serially diluted (1:10, 1:100, 1:1000) using a standard neutralizer and 2 × 0.1 mL of the undiluted sample and 0.5 mL of the diluted sample was spread onto the plates. Eunumeration was taken out by weighted average colony forming unit values recorded from each media.
Matrix‐assisted laser desorption ionization‐mass spectrometry (MALDI‐MS) profiling was used to identify microorganisms using whole‐cell profile mass spectra.
Bacterial biodiversity, genetic variations in bacterial DNA fragments, was determined by single‐stranded conformation polymorphism (SSCP) [6]. Bacterial DNA was subjected to PCR amplification of the16S rRNA gene, denaturation, reannealing, gel electrophoresis, and gel staining. The gel image was captured by using a gel documentation system and image analysis software was used to detect and quantify the bands present.
The Shannon index considers the number of different DNA sequence variants (bands) observed in SSCP analysis and was calculated using the following formula, where the species richness was calculated from the number of bands from the SSCP test:
3.3. Assessment of Skin Status
The skin condition was assessed by the study physician using the Three Item Severity score (TIS score) [7] before and after 1 week of wearing the detergent‐washed cloth. The TIS score summarizes the intensity of erythema, edema/papules, and excoriation. The intensity of each symptom is rated on a scale of 0 to 3 and then summed to a maximum score of 9. The higher the TIS score, the more pronounced the clinical picture.
In addition, the subjects rated daily the itchiness of their skin, tolerability of the product, and the odor of the product during 1 week of wearing the detergent‐washed cloth, using a rating scale of 0 (very bad) to 10 (very good).
3.4. Statistics
To determine the statistics in this study, the software Statistica (Statsoft and TIBCO Software Inc) was used, and the Wilcoxon test was applied. A p‐value below 0.05 was considered as significant.
4. Results
The aim of this study was to evaluate the tolerability of two detergents (Persil Megapearls Sensitive and Persil Sensitive Gel) on adults with AD.
To determine the microbiome on subject skin swab samples, bacterial culture revealed three main morphologies to be Staphylococcus saprophyticus/Staphylococcus haemolyticus, Staphylococcus cohnii/Staphylococcus hominis/Staphylococcus capitis, and Staphylococcus epidermidis, representing over 99% of cultivatable bacteria (which was confirmed by Matrix‐assisted laser desorption ionization [MALDI]‐biotyping of randomly selected colonies (data not shown)). S. aureus was not identified. Total viable counts (TVCs) were conducted to determine the impact of the detergents on the microbiome viability. For Persil Sensitive Gel, TVC on Day 7 versus Day 0 did not reveal a significant change in the microbiome population (p‐value = 0.72), inferring no influence on microbiome viability, while there was a slight increase in TVC for Persil Megapearls Sensitive on Day 7 versus Day 0 (p‐value = 0.008), inferring a positive impact on the microbiome (Figure 1A,B, respectively). Similarly, a Staphylococcus colony count was conducted in selective media showing comparable results where Persil Sensitive Gel did not have an impact on Staphylococcus viability (p value = 0.72) and Persil Megapearls Sensitive showed a slight increase (p value = 0.02) (Figure 1C,D, respectively).
Figure 1.
Total viable count (TVC) comparison of Persil Sensitiv Gel and Persil Megapearls Sensitiv on Day 0 and Day 7 in terms of (A and B) and a Staphylococcus colony count (C and D), respectively.
To determine bacterial biodiversity, SSCP was conducted on Day 0 and Day 7 skin swab samples revealing a good profile match of the paired samples before versus after treatment for both detergents (data not shown). Some differences were observed in non‐identified bands (further investigation possible). Importantly, no S. aureus bands were detected while S. epidermidis profiles remained unchanged. A Shannon index calculation, quantitatively measuring how many different types of bacterial species were present in the data set, did not reveal a statistical difference in either of the detergents (Persil Sensitiv gel p value = 0.88; Persil Megapearls Sensitiv p value = 0.49) between Day 7 versus Day 0, indicating that there was no impact of the detergents on the bacterial biodiversity (Figure 2).
Figure 2.
Bar chart comparison of the Shanon index on Day 0 and Day 7 for Persil Senitive Gel (A) and Persil Megapearls Sensitive (B).
A subject‐reported TIS score was used to determine if the detergents had any effects on AD, on Day 0 versus Day 7 of the study. Before the testing with Persil Megapearls Sensitive, the average TIS was 1.00 (SD ± 1.15) and remained 1.00 (SD ± 1.15) after 1 week of testing. This indicates that the lesions remained stable without any change. Before testing with Persil Sensitiv Gel, the average TIS was 1.05 (SD ± 1.05) and increased to 1.10 (SD ± 1.06) after 1 week of testing, suggesting an improvement of the lesions.
All subjects were then asked to report on the detergent's general tolerability and impact on allergic symptoms. The average tolerability rating was 9.86/10 (SD ± 0.35) and 9.67/10 (SD ± 0.90) for Persil Megapearls Sensitive and Persil Sensitive Gel, respectively. The average rating on pruritus was at 0.12/10 (SD ± 0.30), and 0.62/10 (SD ± 1.64) for Persil Megapearls Sensitive and Persil Sensitiv Gel, respectively, indicating no itch at all.
5. Conclusions and Perspectives
The primary aim of this study was to determine the “microbiome‐friendly” properties of laundry detergents through the assessment of skin microbiome samples from volunteers suffering from AD. AD patients were purposefully selected as they have a sensitive skin barrier and an easily dysbalanced microbiome [8]. We assume that the findings could be generalized to non‐atopic populations as currently they are regarded as having a more stable microbiome of the skin than AD patients. The key measures considered in the evaluation of the detergents were the growth of Staphylococcal bacteria, the detergent's impact on bacterial diversity, and the subjects' tolerability toward these products. The results regarding skin microbiome showed no negative shift of the microbes indicating that there were not any microbiome‐disbalancing remnants of the tested detergents remaining on the washed clothes. The pathogenic S. aureus could not be identified in the skin samples which is an indirect sign for the perseverance of skin‐friendly bacteria. This study also revealed that the general tolerability of the laundry detergents was high and that the laundry detergents did not have any worsening effects on AD condition in terms of itch.
The use of Persil Megapearls Sensitiv and Persil Sensitiv Gel laundry detergents had no negative impact on the microbiome which is crucial for people with sensitive skin and allergies. This is an indirect sign that skin‐friendly bacteria of the healthy microbiome are not affected. Importantly, this study also confirms that ECARF‐certified products are indeed allergy‐friendly, even at the microbiome level.
To the best of our knowledge, this study is the first to examine the microbiome‐friendliness of laundry detergents in human subjects. There are some limitations in this study that could be regarded in the future, such as: (i) continuous and tight contact of the feet with socks limits the generalizability of the findings to other body parts where different microorganisms may constitute a healthy microbiome [9], or (ii) the tolerability of the detergents in other skin conditions, and (iii) the subjects' personal hygiene habits were not controlled, for which future studies may consider instructing the subjects with a predetermined personal hygiene protocol. In recent reports detailing newly licensed drugs for AD there are notable differences in drug efficacy across distinct anatomical regions, for example in the extremities compared with the trunk of the body, however, it has not been addressed if the observed differences are due to variations of the microbiome in the distinct body parts [10, 11, 12].
In conclusion, this study provides valuable information about laundry detergent effects on microbiome fluctuations and influence on skin‐allergic symptoms of AD patients. The results of this study suggest that AD patients can use the tested laundry detergents without any concerns of negative impacts on their skin condition. Given the significance of maintaining a healthy skin microbiome, further research in this area is crucial to develop recommendations for maintaining skin health.
Author Contributions
Demetrios Christou: conceptualization, writing–original draft, writing–review and editing. Katarina Stevanovic: conceptualization, formal analysis, writing–original draft, writing–review and editing. Stefan Evers: data curation, formal analysis, methodology, writing–review and editing. Mirko Weide: formal analysis, methodology, writing–review and editing. Torsten Zuberbier: conceptualization, data curation, formal analysis, methodology, writing–review and editing.
Conflicts of Interest
Stefan Evers is an an employee of Henkel AG & Co KGaA, which are producing, for example, laundry detergents, but the payment and his employer have no direct contribution to the content of this article. Mirko Weide is an employee of Henkel AG & Co KGaA, which produce, for example, laundry detergents, but the payment and his employer have no direct contribution to the content of this article. Torsten Zuberbier has received institutional funding for research and/or honoria for lectures and/or consulting from Amgen, AstraZeneca, AbbVie, ALK, Almirall, Astellas, Bayer Health Care, Bencard, Berlin Chemie, FAES, HAL, Henkel, Kryolan, Leti, L'Oreal, Meda, Menarini, Merck, MSD, Novartis, Pfizer, Sanofi, Stallergenes, Takeda, Teva and UCB, Uriach; in addition, he is a member of ARIA/WHO, DGAKI, ECARF, GA2LEN, and WAO. The other authors declare no conflicts of interest.
Transparency Statement
The lead author Torsten Zuberbier affirms that this manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned (and, if relevant, registered) have been explained.
Acknowledgements
The authors would like to thank the volunteers participating in the study. Also, thanks to Martina Seiler, Detlef Buisker, Michael Kandzia, Rainer Simmering, and AMODIA Bioservice GmbH, Braunschweig (Germany) for general support of the project. Open Access funding enabled and organized by Projekt DEAL.
Demetrios Christou and Katarina Stevanovic contributed equally to this study.
Data Availability Statement
Individual participant data that underlie the results reported in this article, after deidentification (text, tables, figures, and appendices), and the study protocol, will be available immediately following publication with researchers whose proposed use of the data has been approved by T. Zuberbier.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
Individual participant data that underlie the results reported in this article, after deidentification (text, tables, figures, and appendices), and the study protocol, will be available immediately following publication with researchers whose proposed use of the data has been approved by T. Zuberbier.