Cats often poop outside the litter box due to a combination of medical, environmental, and behavioral reasons.

Medical Issues

Health problems such as constipation, diarrhea, urinary tract infections, kidney disease, arthritis, or inflammatory bowel disease can make it difficult or painful for cats to use the litter box properly, leading them to poop elsewhere.

Environmental and Stress Factors

Cats are sensitive to changes around them. Stressful changes like moving to a new home, adding a new cat to the household, or relocating the litter box can cause anxiety, which sometimes results in pooping outside the box. The litter box location and cleanliness are also critical. Cats prefer a quiet, private, and clean area for their litter box. If the box is dirty, too small, in a noisy or frequently trafficked area, or if the type of litter is not to their liking (e.g., scented litter), they may avoid it.

Behavioral Issues

Behavioral reasons include territorial marking when new cats are introduced or stress-induced changes in habit. If another cat guards the box or if the cat associates the box with negative experiences, it may choose other places to poop.

Solutions

To stop this behavior, veterinary consultation is important to rule out health problems. Maintaining a clean litter box, possibly adding more boxes (one more than the number of cats), changing the litter type to an unscented one, placing the boxes in quiet, accessible areas, and cleaning any soiled areas with enzymatic cleaners are effective steps. Blocking access to favorite inappropriate elimination spots with obstacles or deterrents can also help.

In summary, a cat pooping outside the litter box is often a sign of discomfort, either physical or psychological, and attending to these can help resolve the issue.