Humic Acids

Chemical Compounds

Also: HA, humic acid, humate, sodium humate, potassium humate

CAS: 1415-93-6

Molecular weight: 10,000–100,000+ Da

Solubility: Insoluble at pH < 2, soluble at higher pH

Concentration in peat: 10–40% of dry mass

Humic acids are high-molecular-weight organic polymers formed during the decomposition of plant material in peat bogs. They are the primary bioactive fraction of peat and the most studied component in cosmetic and balneological applications.

Structure

Complex polymers containing aromatic rings, carboxyl groups (–COOH), phenolic hydroxyl groups (–OH), and quinone structures. Dark brown to black in color. The structural complexity gives humic acids their multi-functional biological activity — the same molecule exhibits anti-inflammatory, antioxidant, antimicrobial, and chelating properties simultaneously.

Extraction

Extracted from peat using alkaline solutions (NaOH or KOH), then precipitated by acidification to pH < 2. The extraction method affects the biological activity of the resulting humic acid preparation. Water-extractable fractions have different properties than alkali-extracted fractions.

Cosmetic Relevance

The most important compound for cosmetic peat applications. Anti-inflammatory and antimicrobial properties make humic acids relevant for inflammatory skin conditions (psoriasis, eczema, seborrheic dermatitis). Chelation properties contribute to mineral delivery in balneotherapy. Used in face masks, bath preparations, scalp treatments, and body wraps.

Evidence & Claims

exhibits anti-inflammatory (strong)

Inhibits pro-inflammatory cytokines TNF-α, IL-1β, IL-6; dose-dependent bimodal effect; suppresses allergic contact dermatitis

van-rensburg-2015 — Section 3.2 — cytokine inhibition in vitro

klocking-2005 — Review of anti-inflammatory activity of humic substances

cheleschi-2020 — In-vitro evidence of anti-inflammatory pathways in balneotherapy

flaig-1992 — Links humic substance chemistry to therapeutic effects

blonska-sikora-2024 — Anti-inflammatory properties in cosmetological context

ubner-2013 — HA dose-dependent: 10–80 μg/ml increases TNF-α 3× (pro-inflammatory), >100 μg/ml decreases TNF-α 10× (anti-inflammatory) — Junek et al. 2009 via review

verrillo-2022 — Lignite-derived HA significantly decreased IL-6 and IL-1β gene expression in HaCaT keratinocytes; protective against Urban Dust damage

zhernov-2020 — Topical peloid-derived HA suppressed IFN-γ, IL-4, IL-10, IL-13, IL-17, TNF-α in DNCB-induced ACD mice; reduced serum histamine

gvozdeva-2025 — 2025 review confirms HA anti-inflammatory properties via cytokine modulation and ROS scavenging

exhibits antioxidant (moderate)

Free radical scavenging via phenolic hydroxyl groups

van-rensburg-2015 — Section 3.4 — antioxidant capacity measurements

exhibits antimicrobial (moderate)

Active against gram-positive bacteria and some fungi via membrane disruption; antiviral by blocking virus attachment to cells

ansorg-1978 — MIC values against S. aureus and E. coli

ubner-2013 — HA blocks virus replication by occupying positively charged glycoprotein regions needed for cell attachment; most HA showed antibacterial activity in vitro (Ansorg, Rochus 1978)

gvozdeva-2025 — Review confirms HA antimicrobial and antiviral properties including viral fusion inhibition; references HS-Zn/Se complexes inhibiting SARS-CoV-2

exhibits immunomodulatory (moderate)

TPP (Tolpa Peat Preparation) from peat HA registered as immunomodulator in Poland; stimulates interferon-α, interferon-γ, TNF-α synthesis

ubner-2013 — TPP registered as immunomodulator drug in Poland; optimal cytokine stimulation at 10–100 μg/ml; stimulates neutrophils and macrophages

exhibits hyaluronidase-inhibition (preliminary)

Neutralizes hyaluronidase enzymes, extending natural hyaluronic acid lifespan in skin

hinn-2026 — Humic acid neutralizes hyaluronidase — citing Efert 2018 via Estonian literature

exhibits keratolytic (preliminary)

Mild softening and removal of dead skin cells

wollina-2009 — Review: peat application helps with scaling and plaque reduction in psoriasis — keratolytic component

exhibits chelation (strong)

Binds heavy metals and mineral ions via carboxyl and phenolic groups

stevenson-1994 — Chapter 9 — metal-humic complexation