Covered vs uncovered litter box: what the research actually says

The short answer

Most cats don’t care whether the box has a lid, as long as it’s big enough and clean enough. The most-cited research on this, a peer-reviewed 2013 study by Grigg et al. published in the Journal of Feline Medicine and Surgery, found no significant difference in litter box use between covered and uncovered boxes. About 70% of cats in that study showed no preference either way, while 15% leaned covered and 15% leaned uncovered. If you’re choosing based on your own preferences (odor containment, aesthetics, litter scatter), that’s fine. Just don’t assume a cover fixes behavior problems, because in some situations it can make them worse.

Why the “cats hate covered boxes” claim is oversimplified

A lot of owners have absorbed the idea that cats universally prefer open boxes. That’s not quite what the science shows. Most cats don’t have a strong preference, but there’s an important asterisk: the boxes used in the Grigg study were larger than the commercially available covered boxes most people actually buy. That matters because cats consistently show a preference for bigger litter boxes than what’s sold in stores, and separate research on litter box size found that doubling box size can meaningfully increase how reliably a cat uses it. A 2025 study on box size and litter type preference found cats favored boxes measuring at least roughly 50 cm, paired with clumping clay litter.

Put those two findings together and you get the real nuance: covered boxes aren’t inherently disliked, but covered boxes as they’re typically sold (smaller, boxier, cramped) can be. A roomy covered box with a good-sized footprint is a different animal than the compact hooded box on the bottom shelf at the pet store.

Where covered boxes cause real problems

Covered boxes aren’t just a coin flip. In certain real-world conditions, they carry documented downsides that go beyond preference:

Trapped ammonia. Poor ventilation and low airflow inside a hood trap ammonia gas near the box. Cats have a far more sensitive sense of smell than we do, and vets note that a covered box’s concentrated ammonia can be overwhelming enough to cause litter avoidance. Prolonged exposure can irritate the respiratory tract or aggravate conditions like asthma.
Hidden waste, hidden illness. Cornell’s Feline Health Center points out that covered boxes trap odor inside rather than letting it dissipate, and that matters for more than smell: you can’t casually notice changes in urine volume, color, frequency, or stool consistency if the box interior is hidden. Those changes are often the earliest warning signs of chronic kidney disease, urinary tract infections, diabetes, or hyperthyroidism. Owners who never look inside the box tend to catch these problems later.
Ambush risk in multi-cat homes. A covered box has one entry and exit. In a multi-cat household, a more dominant cat can guard that opening from outside, effectively trapping the cat inside without you noticing. Veterinary behaviorists connect this stress dynamic to feline idiopathic cystitis and other stress-linked urinary conditions, since a covered box also blocks a cat’s sightline to approaching housemates.
Scent overload. If you’re using scented litter, a cover concentrates the fragrance along with the ammonia. One cat in the original study that had been avoiding a covered box started using it again as soon as the litter was switched to an unscented brand.

None of this means every covered box causes disease. It means covered boxes remove a layer of information and protection that costs you nothing to keep with an open box.

The bigger factor: cleanliness, not the lid

Across the research, cleanliness matters more than cover type. If boxes are scooped at least once daily, most cats stop showing any preference between covered and uncovered setups. The lid becomes largely irrelevant once the box itself is well maintained. The catch is that covered boxes are scooped less often in practice, largely because they’re out of sight and, as the phrase goes, out of mind. If you go with a covered box, you have to be more deliberate about a daily scooping habit than you would with an open box that reminds you every time you walk past it.

When to skip covered boxes entirely

If your cat is already having litter box issues, covered boxes are one of the first things vets tell you to remove. The ASPCA specifically recommends taking covers (and liners) off all boxes when addressing elimination problems. Vets also flag covered boxes as a no-go for cats with any existing urinary or behavioral issues, since the trapped ammonia smell can be aversive enough on its own to trigger avoidance. That said, cats with elimination disorders can have unusual, individual preferences, and some behaviorists do include a covered option in a