Greetings, 

Thanks for reaching out, while this is outside the core of OSU Extension’s agricultural programs, we can share general, research‑informed guidance and point you toward reliable Extension and EPA resources.

Why the odor is showing up now
Cat urine contains uric acid crystals that bind tightly to porous materials such as cardboard, paper, fabric, and unfinished wood. These crystals are not water‑soluble, so the odor can persist for years and can be reactivated when items are moved or exposed to humidity.
Even if the original spray site was elsewhere, odor molecules can settle on stored items through airflow and shared indoor spaces, which matches what you’re seeing.

What Extension and EPA sources recommend
University Extension programs consistently note that some items simply cannot be salvaged once urine odor has deeply penetrated. For items that may be recoverable:

• Use an enzymatic cleaner
  Look for products labeled for urine odor removal that contain enzymes capable of breaking down uric acid crystals.
  Extension resources:
• University of Nebraska–Lincoln Extension: guidance on removing pet urine odors
• University of Georgia Extension: cleaning and household odor removal
• EPA guidance on safe use of cleaning products and avoiding ozone generators
• Sunlight and ventilation
  Many Extension programs recommend placing items outdoors in direct sunlight with good airflow. UV exposure can help break down odor compounds.
• Avoid ozone generators
  EPA and multiple Extension programs warn that ozone can damage materials and is not effective on uric acid–based odors.
• Contain questionable items
  If items still have a strong odor, store them in sealed plastic bins to prevent odor transfer to other belongings, especially in a shared storage unit.

When disposal is the recommended option
Extension guidance generally recommends discarding porous items (cardboard boxes, books, papers, some fabrics) if:

• Odor remains after enzymatic treatment, or
• Items have been saturated for a long period (months to years)

Given that these items have been sitting undisturbed for two years and the odor is overwhelming when moved, disposal may be the most practical and protective option — especially since the owner is preparing for a move and needs a quick solution.
If professional help is needed - Look for:

• Certified odor remediation specialists