USPS Packaging Instruction 6C

Category B Infectious Substances

Infectious substance means a material known or reasonably expected to contain a pathogen. A pathogen is a microorganism that can cause disease in humans or animals. Examples of pathogens include bacteria, viruses, fungi, and other infectious agents. An infectious substance must be assigned to one of the following two packaging categories:

Proper Shipping Name and ID Number


Required Packaging

Primary Receptacle (Container)
Cushioning and Absorbent Material
Secondary Container
Outer Shipping Container

As required by 49 CFR 173.199:

International Mail

Note: Countries distinguish between infectious and noninfectious (nonregulated) biological substances and may prohibit one or the other or both. See “Prohibitions” in the Individual Country Listings.