A cat suddenly avoiding the litter box is one of the most common reasons owners consider rehoming a cat, and it's also one of the most commonly misdiagnosed as "bad behavior" when a real medical cause is actually driving it.
Rule out medical causes first, every time
Any sudden litter box avoidance in a previously reliable cat warrants a vet visit before assuming this is a behavioral or environmental issue. Urinary tract infection, FIC (feline idiopathic cystitis), bladder stones, and arthritis (which can make climbing into a high-sided box genuinely painful) are all common medical causes that present exactly like a "behavior problem" to an owner who isn't aware of them.
A cat associating pain with the box will avoid the box
If a cat experienced pain during urination while using the litter box — even once, from a resolved UTI — they can form a lasting negative association with that specific box or location, continuing to avoid it even after the medical issue is treated. This is why a location change, alongside medical treatment, sometimes helps even after the underlying medical cause is resolved.
Once medical causes are ruled out, check the setup itself
The general rule of one box per cat plus one extra applies here specifically — an inadequate number of boxes, boxes placed too close together, or boxes in a noisy or high-traffic location are all genuine, fixable causes of avoidance that have nothing to do with the cat's temperament.
Litter type and depth matter more than owners expect
Most cats prefer unscented, fine-grained clumping litter over scented or coarse alternatives — a switch to a heavily fragranced litter, intended to make things more pleasant for the owner, is a surprisingly common trigger for avoidance. Roughly 2 inches of litter depth is generally preferred over a very shallow or very deep layer.
Covered boxes and liners: often owner preference, not cat preference
Covered boxes trap odor inside (unpleasant for a cat with a much more sensitive sense of smell than a human), and litter liners can catch claws or create an unfamiliar texture change. Both are more often chosen for owner convenience than cat preference, and removing either is a reasonable, low-cost experiment if avoidance is happening.
Cleaning frequency
Daily scooping, with a full litter change and box wash roughly weekly, is the realistic standard — a box that's gone several days without scooping is a common, avoidable cause of a cat choosing an alternative location.
If avoidance persists despite a good setup and a clean medical workup
At this point, a formal consultation with a veterinary behaviorist is genuinely worthwhile — this is a solvable problem in the significant majority of cases, but persistent cases sometimes need a level of individualized behavioral assessment beyond what a general environmental checklist can address.