Tannins

Tannins are the compounds that make red wine dry, green tea astringent, and peat bogs hostile to bacteria. They’re a subclass of phenolic compounds — larger, more complex, and with a distinctive ability to bind to proteins. In peat, they contribute to the acidic environment, the brown colour, and much of the antimicrobial and skin-toning activity.

What tannins do

Tighten skin on contact. Tannins are classical astringents. They work by precipitating proteins on the skin surface — forming a thin, tight protein layer that constricts pores and firms texture (Scalbert 1991). This is the immediate “tightening” you feel when a peat face mask dries on your skin. The effect is temporary (hours, not days) but visible, and it’s the same mechanism behind witch hazel and other botanical toning products.

Suppress microbes. Tannins inhibit microbial enzymes and starve microorganisms by binding the proteins and nutrients they need to grow (Scalbert 1991). This antimicrobial action complements the broader antimicrobial effects of humic acids and is part of the reason peat bogs are so effective at preservation — the tannins literally tan organic tissue, the same chemistry behind leather production.

Scavenge free radicals. Like other polyphenolics, tannins are effective antioxidants — they neutralise free radicals and chelate pro-oxidant metals like iron and copper that would otherwise catalyse oxidative damage (Rice-Evans 1996).

Types in peat

Peat contains both condensed tannins (proanthocyanidins — the same compounds found in grape seeds and pine bark) and hydrolysable tannins. Condensed tannins predominate in sphagnum-derived peat.

As peat ages and humification progresses, free tannins are gradually incorporated into the humic substance matrix — becoming structural components of humic and fulvic acid molecules rather than existing independently. This means less-decomposed peat has more free tannins available for direct skin contact, while highly humified peat has more tannins locked into the humic structure.

Where tannins matter most

Tannins are most relevant in applications where direct skin contact delivers the astringent and antimicrobial effects:

• Face masks — the tightening and toning sensation is primarily tannin-driven
• Scalp treatments — antimicrobial contribution to dandruff and seborrheic dermatitis management
• Foot soaks — antimicrobial environment for fungal infections

The tanning effect — tannins cross-linking collagen fibres — is also the mechanism behind peat’s extraordinary preservation of bog bodies. The same chemistry that preserved Tollund Man’s face for 2,400 years temporarily firms your skin during a face mask treatment. Different scale, same principle.