Tannin

A class of polyphenolic compounds present in sphagnum moss and other bog plants, named (via French/English usage) for their historical role in tanning leather — the same protein-binding chemistry that toughens hide also gives tannins their astringent, “tightening” effect on skin and mucous membranes.

Plain-Language Summary

Two structural types occur in peat: condensed tannins (proanthocyanidins, the dominant type in sphagnum-derived peat) and hydrolyzable tannins. Tannins are part of what makes fresh bog water and young peat taste bitter and look tea-colored — the same tannin-driven staining is why bog pools and bog-adjacent streams often run brown. As peat humifies, free tannins are progressively absorbed into the growing humic-substance matrix, so their concentration is highest in young, lightly decomposed peat and falls with depth/age — see Humification.

What They Do

Classic astringents: they precipitate proteins and tighten tissue, which is the chemical basis for using peat/tannin-containing preparations in toning and pore-tightening cosmetic applications. Independently antimicrobial and antioxidant.

Where the Data Lives

This page is a plain-language orientation. For the full evidence-graded list of biological activities and the specific studies behind each claim, see Tannins.