# Biological substance, Category B — Postal shipping restrictions by item category

For Biological substance, Category B, carrier is USPS; restriction type is restricted; scope is domestic mail (air and surface); conditions is Hazard class 6.2, UN3373, packing group n/a; domestic mail air: 6C; domestic mail surface: 6C, recorded from its source on 2026-08-10.

- **Item category:** Biological substance, Category B _(verified: appears in the quote below)_
- **Carrier:** USPS _(our reading, not quoted from the source)_
- **Restriction type:** restricted _(our reading, not quoted from the source)_
- **Scope:** domestic mail (air and surface) _(our reading, not quoted from the source)_
- **Conditions:** Hazard class 6.2, UN3373, packing group n/a; domestic mail air: 6C; domestic mail surface: 6C _(verified: appears in the quote below)_

## What the source says

> Biological substance, Category B 6.2 UN3373 n/a 6C 6C

## Source

- https://pe.usps.com/cpim/ftp/pubs/pub52/pub52.pdf

Last verified: 2026-08-10. Review by: 2027-08-10.
Part of [Postal shipping restrictions by item category](https://referencesource.org/shipping-restrictions-by-class/).