Common skin cleansers caused small temporary decreases in the antimicrobial peptide LL-37 on skin but did not disrupt the skin microbiome or increase vulnerability to infection in the short term.
No significant microbiome change after washingDespite speculation that skin cleansers might disrupt the protective microbiome, no significant changes in bacterial community abundance or diversity were detected after washing with common cleansers.
What the researchers found
Washing with common skin cleansers produced small but statistically significant decreases in LL-37 antimicrobial peptide levels on the skin surface shortly after washing. However, no significant changes were detected in bacterial community abundance or diversity. Group A Streptococcus did not survive better on washed skin compared to unwashed skin.
In contrast, soaps containing antimicrobial compounds (benzalkonium chloride or triclocarban) decreased the growth of Group A Streptococcus applied after rinsing, demonstrating that antimicrobial soap additives provide an additional protective effect beyond the mechanical cleaning action.
Why it matters
The skin microbiome and antimicrobial peptides are increasingly recognized as essential components of immune defense. As public health messaging emphasizes hand washing for infection prevention, it's important to confirm that this practice doesn't undermine the skin's natural protective systems. This study provides evidence that short-term washing is safe for the skin's innate defense mechanisms, supporting continued hand hygiene recommendations.
How the study worked
Human forearms were washed with several common skin cleansers. Researchers then measured the abundance of the antimicrobial peptide LL-37 on the skin surface, assessed bacterial DNA abundance and diversity through microbiome analysis, and tested whether Group A Streptococcus could survive better on washed versus unwashed skin. Soaps with and without antimicrobial additives were compared.
What this study cannot tell us
The study only examined short-term (acute) effects of a single washing event. Long-term effects of chronic, repeated washing — as would occur with healthcare workers washing hands dozens of times daily — were not assessed. The study used a limited number of cleanser types, and results may not generalize to all skin care products. Individual variation in skin microbiome composition and LL-37 production was not extensively characterized.
How to read the evidence
This is a human experimental study with a controlled design, providing direct evidence about the short-term effects of skin cleansing on antimicrobial peptides and the microbiome. However, the short observation period and limited scope (single wash event) constrain the conclusions that can be drawn about long-term effects.
When this study was published
Published in 2016, this study remains relevant to ongoing discussions about skin hygiene and microbiome health. The findings are consistent with subsequent research supporting the safety of standard hand washing practices.
The bigger picture
This study sits at the intersection of microbiome science, antimicrobial peptide biology, and public health hygiene practices. As the skin microbiome field has grown, some popular media narratives have questioned whether modern hygiene practices might be harmful by disrupting natural defenses. This research directly addresses that concern and provides evidence-based reassurance that standard hand washing practices are compatible with maintaining the skin's antimicrobial peptide defense system.
Questions still open
- Does chronic, repeated hand washing over weeks or months have a cumulative effect on LL-37 levels and microbiome composition that single-wash studies miss?
- Are there specific populations (such as those with eczema or compromised skin barriers) where washing might more significantly deplete antimicrobial peptides?
- Could skin care products be designed to maintain or replenish LL-37 levels after washing?
Common questions
What is LL-37 and why is it important for skin health?
Should I worry that hand washing is harming my skin's natural defenses?
Read the original research
The Cutaneous Microbiome and Aspects of Skin Antimicrobial Defense System Resist Acute Treatment with Topical Skin Cleansers.
The Journal of investigative dermatology, 136(10), 1950-1954
Citation
Two, Aimee M; Nakatsuji, Teruaki; Kotol, Paul F; Arvanitidou, Evangelia; Du-Thumm, Laurence; Hata, Tissa R; Gallo, Richard L. (2016). The Cutaneous Microbiome and Aspects of Skin Antimicrobial Defense System Resist Acute Treatment with Topical Skin Cleansers.. The Journal of investigative dermatology, 136(10), 1950-1954. https://doi.org/10.1016/j.jid.2016.06.612