Humic Acids

If peat has a single star ingredient, this is it. Humic acids are large, complex organic molecules — dark brown to black, formed over millennia as plant material decomposes in waterlogged bogs. They make up 10–40% of peat’s dry mass and are responsible for most of the therapeutic effects that European spa medicine has observed for two centuries.

What makes humic acids unusual is their versatility. A single molecule simultaneously exhibits anti-inflammatory, antioxidant, antimicrobial, and chelating properties. Most pharmaceutical compounds do one thing well. Humic acids do several things at once — less potently than a targeted drug, but through multiple pathways that work together.

What humic acids do

Fight inflammation — through the same pathways as ibuprofen. Humic acids suppress the inflammatory signalling molecules TNF-α, IL-1β, and IL-6 (van Rensburg 2015, Klöcking 2005). These are the same signals that NSAIDs and biologic drugs target. In skin cells, humic acids from lignite significantly decreased IL-6 and IL-1β gene expression and protected keratinocytes against urban dust damage (Verrillo 2022). In a mouse model of allergic contact dermatitis, topical peat-derived humic acids suppressed a broad panel of inflammatory cytokines including IFN-γ, IL-4, IL-17, and TNF-α, and reduced serum histamine (Zhernov 2020).

There’s a fascinating dose-dependent twist: at low concentrations (10–80 μg/ml), humic acids actually increase TNF-α production by 3×. Above 100 μg/ml, they flip and decrease it by 10× (Übner 2013, citing Junek et al. 2009). A direct primary study of the same effect confirms it: low-concentration peat-derived humic acid raised TNF-α release roughly 3-fold in stimulated immune cells, reversing to a decrease at higher concentrations — while fulvic acid, tested alongside it, never triggered the pro-inflammatory phase at any concentration (Klöcking 2008). This bimodal behaviour explains why whole-peat applications — which deliver high concentrations — are anti-inflammatory, while very dilute preparations may have the opposite effect.

Kill bacteria and viruses. Of 81 natural humic acid preparations tested, 57 showed antimicrobial activity against a panel of microorganisms (Ansorg 1978). The mechanism involves disrupting bacterial cell membranes and, for viruses, occupying the positively charged glycoprotein regions that viruses need to attach to host cells (Übner 2013). A 2025 review confirms antiviral properties including viral fusion inhibition (Gvozdeva 2025). The strongest antiviral potency data in the whole knowledge graph for this compound class comes from a coal-derived relative rather than peat itself: oxihumate blocked HIV-1 infection of cultured cells at a low concentration (IC50 12.5 µg/ml), with no resistance developing over 12 weeks of exposure (van Rensburg 2002). It’s not peat-specific, but it demonstrates what the humic-acid structure is capable of.

Protect against oxidative damage. The phenolic hydroxyl groups in humic acids donate hydrogen atoms to neutralise free radicals — the same mechanism behind vitamin C and vitamin E, but delivered in a complex organic matrix (van Rensburg 2015). In an ex-vivo model using human placental mitochondria, Tolpa Peat Preparation reduced lipid-peroxidation markers with antioxidant capability comparable to vitamin E itself (Piotrowska 2000).

Filter UV radiation. Humic acids share a structural feature with melanin and absorb ultraviolet light strongly — 60–84% of UV-B and around half of UV-A at moderate concentrations. In cultured skin cells, that translated into real protection: cells shielded by a humic-acid layer before UV-B exposure suffered over 60% less cytotoxic damage, performing comparably to PABA, a reference sunscreen ingredient (Seel 2012). This is preliminary, in-vitro evidence only — no clinical or ex-vivo skin study has tested it — but it points to a possible photoprotective role alongside humic acid’s other effects on skin aging and rosacea, where UV exposure is a known trigger.

Preserve your skin’s hyaluronic acid. Humic acids neutralise hyaluronidase, the enzyme that breaks down hyaluronic acid in skin (Hinn 2026). This is the mechanism behind many expensive anti-aging serums — but instead of adding synthetic hyaluronic acid, humic acids help your skin keep the hyaluronic acid it already produces.

Chelate minerals. The carboxyl and phenolic groups in humic acids bind metal ions — iron, zinc, magnesium — keeping them bioavailable while controlling their reactivity (Stevenson 1994). Isolated humic acid shows this directly: extracted from whole peat, it had over twice the ion-exchange capacity and 120% more total sorption capacity than the raw material it came from, confirming that humic acid — not the peat matrix generally — carries most of peat’s mineral-binding capacity (Gierlach-Hladon 2008). In balneotherapy, this chelation enables mineral delivery through the skin during treatment.

In peat

Humic acids typically make up 10–40% of peat’s dry mass, depending on the source. Estonian peat reaches up to 39.3% in some deposits — among the highest measured (Orrù 2011). Finnish peat averages 24.8–26.8% across sphagnum and sedge types (Korhonen 2008). The quality threshold for balneological peat is generally set at >20% humic acid by dry weight.

Concentration increases with depth and humification — the more decomposed the peat, the more humic acid it contains. This is why cosmetic peat is sourced from deep, highly humified layers (H6–H8+ on the von Post scale), not from the surface.

How it’s studied

Humic acids are extracted from peat using alkaline solutions (sodium or potassium hydroxide), then separated by acidification below pH 2 — the humic acid precipitates while fulvic acids remain in solution. This extraction method matters: water-extractable fractions have different properties than alkali-extracted ones, and the biological activity of any humic acid preparation depends on how it was prepared.

In Poland, a standardised humic acid preparation from peat (Tolpa Peat Preparation, TPP) was registered as an immunomodulatory drug — one of the few cases where a peat-derived compound has achieved pharmaceutical registration (Übner 2013). The primary human-cell data behind that registration: TPP induced dose-dependent interferon and TNF production in human peripheral blood leukocytes at the same 10–100 μg/ml range (Inglot 1993). A small trial in human volunteers taking oral TPP for two weeks found dose-dependent shifts in T-lymphocyte subsets and inflammatory markers — a real signal, though the authors themselves flagged it as preliminary given the small group size and lack of a placebo arm (Baj 1993).

Where it matters

Humic acids are the primary active compound in virtually all peat-based treatments. They’re most relevant for:

• Psoriasis and eczema — anti-inflammatory and keratolytic action
• Seborrheic dermatitis — antimicrobial plus anti-inflammatory
• Skin aging — hyaluronidase inhibition and antioxidant protection
• Joint inflammation — anti-inflammatory compounds absorbed through the skin during peat baths

Every face mask, bath, cream, and scalp treatment that uses whole peat or peat extract delivers humic acids as its primary bioactive component.