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Tannic Acid

  • Acids
  • CAS 1401-55-4

Tannic Acid (CAS 1401-55-4) appears in 1 of the 1,812 car-care products CarCareTruth tracks (as of June 2026). It is readily biodegradable.

Naturally occurring polyphenol from oak bark, galls, and other plant sources. At working concentrations in rust converter formulas (typically 3-5%), the acidic pH of the formula (2.5-3.5) is the primary hazard driver: GHS H315 (skin irritation) and H319 (eye irritation) are consistent with the acidic mixture. Tannic acid itself is low-toxicity by ingestion but the formula should not be ingested. No asthmagen classification, no Prop 65 listing.

Tannic acid is the active ingredient in tannic acid-based rust converters. The plant-derived polyphenol reacts with ferric oxide (rust) through a chelation and complexation mechanism to form ferric tannate, a stable black insoluble compound that bonds to the metal surface and seals it from further oxidation. The conversion reaction is pH-dependent and acid-catalyzed, which is why tannic acid rust converters are formulated at acidic pH (typically 2.5-3.5). Tannic acid is less aggressive than phosphoric acid on skin and does not cause the H314 skin corrosion classification characteristic of phosphoric acid at working concentration.

Health & environment profile

VOC
no
Prop 65 listed
no
Asthmagen
no
EPA Safer Choice
no
Aquatic toxicity
no
Biodegradable
yes
Bioaccumulative
no
Persistent
no
Ozone depleting
no
Microplastic
no
PFAS
no
Env. score
4/5
Purpose: Active rust converter agent; plant-derived polyphenol that reacts with iron oxide (rust) to form ferric tannate, a stable black protective layer

Common questions about Tannic Acid

What is Tannic Acid used for in car care?
Active rust converter agent; plant-derived polyphenol that reacts with iron oxide (rust) to form ferric tannate, a stable black protective layer
Is Tannic Acid a VOC?
No. Tannic Acid is not classified as a volatile organic compound (VOC).
Is Tannic Acid on California's Proposition 65 list?
No. Tannic Acid is not on California's Proposition 65 list.
Is Tannic Acid biodegradable?
Yes. Tannic Acid has a confirmed biodegradable profile.

1 product contain this

Related

Health and environment notes translate the manufacturer Safety Data Sheet, the GHS classification, and authoritative regulatory listings (California Prop 65, EPA). Not medical advice. They describe the ingredient itself; whether a hazard applies to a finished product depends on its concentration and how it's used.