Look for dried white, off-white, or yellowish stains
Check for crusty or stiff patches on the fabric
Inspect areas near the center of the stain for a thicker residue
Use a blacklight in a dark room to look for fluorescent spots
Smell the area for a faint bleach-like or musky odor
Dab the stain with a small amount of cold water to see if it softens
Check whether the stain is on the top surface or soaked through
Compare the stain’s texture to nearby clean fabric
Use a UV stain detection light for better visibility
If needed, test the stain with an enzyme-based laundry product on a hidden area first