Studies on the antimicrobial effect of natural and synthetic humic acids

The earliest systematic characterization of humic acid antimicrobial activity in the knowledge graph, and still regularly cited nearly 50 years later. Published in the German pharmacological journal Arzneimittel-Forschung (Drug Research), this in vitro study is the original evidence for the antimicrobial claims that appear across the substances and applications collections.

Method

Ansorg and Rochus tested 81 natural humic acid preparations and 2 synthetic ones against a panel of microorganisms, measuring minimum inhibitory concentrations (MICs) up to 2500 μg/ml. The preparations varied in source and processing — this variability was deliberate, intended to map the range of antimicrobial activity across different humic acid types.

What It Found

57 of 81 natural preparations showed measurable antimicrobial activity. That 30% did not is as informative as the 70% that did: antimicrobial activity is not a guaranteed property of all humic acids, and source and processing matter. The active preparations showed different spectra — some were more effective against gram-positive bacteria, others against gram-negative — indicating that specific molecular fractions, not humic acids as a bulk class, are responsible for the effect.

How to Read It

This is in vitro evidence from 1978, published in German. It establishes that humic acids can inhibit microbial growth in a laboratory setting at concentrations achievable in therapeutic preparations. It does not prove that topical peat products clear skin infections. But it provides the mechanistic grounding for antimicrobial claims — and the finding that different preparations vary considerably in activity supports the importance of peat quality and sourcing for cosmetic use.