Putting petrolatum on your skin seems to turn up the production of natural germ-fighting chemicals, which might help protect against infections.
Scientific Claim
Petrolatum application is associated with significant upregulation of antimicrobial peptides including S100A8 (fold change 13.04), S100A9 (fold change 11.28), CCL20 (fold change 8.36), elafin (fold change 15.40), lipocalin 2 (fold change 6.94), and human β-defensin 2 (fold change 4.96) in human skin, suggesting a role in enhancing innate immune defense at the skin barrier.
Original Statement
“Significant upregulations of antimicrobial peptides (S100A8/fold change [FCH], 13.04; S100A9/FCH, 11.28; CCL20/FCH, 8.36; PI3 [elafin]/FCH, 15.40; lipocalin 2/FCH, 6.94, human β-defensin 2 [DEFB4A]/FCH, 4.96; P < .001 for all)...”
Evidence Quality Assessment
Claim Status
overstated
Study Design Support
Design cannot support claim
Appropriate Language Strength
association
Can only show association/correlation
Assessment Explanation
The abstract uses language implying induction ('induced expression') but the study design (observational, no randomization/blinding confirmed) cannot establish causation. Verb strength must be downgraded to association.
Gold Standard Evidence Needed
According to GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this specific claim, ordered from strongest to weakest evidence.
Randomized Controlled TrialLevel 1bWhether petrolatum directly causes increased expression of antimicrobial peptides in human skin, independent of occlusion effects.
Whether petrolatum directly causes increased expression of antimicrobial peptides in human skin, independent of occlusion effects.
What This Would Prove
Whether petrolatum directly causes increased expression of antimicrobial peptides in human skin, independent of occlusion effects.
Ideal Study Design
A double-blind, randomized, placebo-controlled trial of 100 healthy adults with symmetric skin sites, applying petrolatum to one forearm and a non-occlusive vehicle to the other, twice daily for 14 days, measuring mRNA and protein levels of S100A8, S100A9, CCL20, elafin, lipocalin 2, and DEFB4A via skin biopsies as primary endpoints.
Limitation: Cannot prove long-term clinical outcomes like infection prevention.
Prospective Cohort StudyLevel 2bWhether petrolatum use over time correlates with sustained antimicrobial peptide elevation and reduced skin infections in at-risk populations.
Whether petrolatum use over time correlates with sustained antimicrobial peptide elevation and reduced skin infections in at-risk populations.
What This Would Prove
Whether petrolatum use over time correlates with sustained antimicrobial peptide elevation and reduced skin infections in at-risk populations.
Ideal Study Design
A 6-month prospective cohort of 200 patients with atopic dermatitis, tracking daily petrolatum use and monthly skin swabs for antimicrobial peptide levels and infection incidence, adjusting for confounders like hygiene and medication use.
Limitation: Cannot rule out unmeasured confounders such as diet or environmental exposures.
Cross-Sectional StudyLevel 3The population-level association between petrolatum use and antimicrobial peptide levels in real-world settings.
The population-level association between petrolatum use and antimicrobial peptide levels in real-world settings.
What This Would Prove
The population-level association between petrolatum use and antimicrobial peptide levels in real-world settings.
Ideal Study Design
A cross-sectional analysis of 500 individuals using petrolatum regularly vs. non-users, measuring skin antimicrobial peptide levels via non-invasive tape stripping and correlating with usage frequency and duration.
Limitation: Cannot determine temporal sequence or causality.
Case-Control StudyLevel 3Whether prior petrolatum use is associated with lower rates of post-surgical skin infections.
Whether prior petrolatum use is associated with lower rates of post-surgical skin infections.
What This Would Prove
Whether prior petrolatum use is associated with lower rates of post-surgical skin infections.
Ideal Study Design
A case-control study comparing 100 patients with post-ambulatory surgery skin infections to 100 matched controls without infection, assessing prior petrolatum use as an exposure variable via structured interview and medical records.
Limitation: Relies on recall and cannot establish biological mechanism.
Systematic Review & Meta-AnalysisLevel 1aThe pooled effect size of petrolatum on antimicrobial peptide expression across multiple human studies.
The pooled effect size of petrolatum on antimicrobial peptide expression across multiple human studies.
What This Would Prove
The pooled effect size of petrolatum on antimicrobial peptide expression across multiple human studies.
Ideal Study Design
A systematic review and meta-analysis of all RCTs and controlled human studies measuring antimicrobial peptide expression after petrolatum application, using standardized methods and outcome definitions, with subgroup analyses by skin condition (e.g., AD, post-surgical).
Limitation: Limited by heterogeneity and quality of included studies.
Evidence from Studies
Supporting (1)
Petrolatum: Barrier repair and antimicrobial responses underlying this "inert" moisturizer.
The study found that putting petrolatum on the skin turns on genes that make natural germ-fighting chemicals, just like the claim said.