I have a female spayed cat in my flat for the last eight months. She used to be stray, I took her in when she was about six months old. So she's about 1,5 years old.

This past month I have noticed that her urine smells very strongly of ammonia - a much, much stronger smell than it used to be. I have NOT changed the type or brand of her litter (I use Ever Clean Multi Crystal), I have NOT changed her eating habits.

I have noticed that lately she likes to drink more water than she used to, but I consider that normal, since it's been getting very hot around here. I also take care to always have water out for her.

What could be causing this smell?

Also, today she has -for the very first time ever- defecated and urinated outside her litter box (in another corner of the bathroom, where her box is). I know this may be due to the fact that her litter box smells much stronger than it used to now, just mentioning it in case there's another connection. Any feedback on this also appreciated.


8 Answers 8


Drinking more water, urine smelling strongly, defecating outside the litter box - all of those signs sound like she's sick. Could be something smallish and easily fixed with a few antibiotics, could be something bigger. Maybe it's something with her kidneys?

My advice: take her to the vet to find out what it is and how it can be treated. I think this is something that can be easily corrected if you act on it now, but I'm just another cat-mom, not a veterinarian.

See if you can determine

  • is she urinating more, less, or about the same?
  • is she eating more, less, or about the same?

Ammonia is present in urine as a by-product of meat consumption, so its presence is entirely natural. The usual reason for an increase in the smell of ammonia in urine is hydration related. The more concentrated the urine, as a result of lack of water in the system, the stronger the smell.

So, the heat situation could be the reason for this, but cats are not big drinkers and I would be suspicious of this as the root cause. Right now this smacks of dehydration and that may be a sign of another problem, potentially serious. I would arrange a visit to the vet as soon as possible just to be safe.

  • There is no ammonia in fresh urine of healthy mammals. If you think different, please supply some references. The suggestion to visit a vet is quite right, but it would appear much more urgent if ammonia in the urine is categorized as sign of a real problem of the urinary tract.
    – Ariser
    Jan 21, 2018 at 17:36

Urea, present in the urine of mammals, naturally degrades into ammonia.

In solid form it is shelf stable, but in solution it is hard to keep from degrading. There are also bacteria and enzymes that are fairly widespread that hasten this decomposition. Even if it is just damp the decomposition can take place.

The strong ammonia smell would suggest an increased load of urea in her urine, increased drinking and peeing could indicate some problem with the kidneys, or metabolism... I'd suggest a vet visit too.


Take her to the vet. This description fits characteristics of Kidney Failure or even Kidney Disease. I know this because my previous cat, may she rest in peace, had a condition with similar signs, if not exact. She was only 2 years when we had to put her down. The earlier the treatment, the longer you can prevent any damage from occurring real fast.


I had a cat that had the same behavior. He suddenly started to sometimes defecate outside the litter box. Then I noticed that he would sometimes cry when he was peeing in the litter box. So I took him to the vet who diagnosed that he had a urinary tract infection. Some cats are prone to urinary tract infection and the vet recommended a special food to avoid it. Slowly he stopped defecating on the floor and returned back to normal behavior with no more problems. You might want to take your cat to the vet.

  • Not 'might' DEFINITELY take your cat to the vet. From your description, it sounds like kidney disease, UTI, there are several possibilities; impossible to diagnose in this forum. She needs labs, an exam, and medication. Untreated, these conditions can cause death and are painful for your cat.
    – M.Mat
    Feb 18, 2017 at 23:13

Fresh urine of healthy mammals usually does not contain ammonia. If it does, something's wrong!

In many cases ammonia in urine is the product of microorganisms able to produce the enzyme urease. With this enzyme they can metabolize urea. So if the freshly dropped urine smells like ammonia, most probably bacteria like "proteus mirabilis" are infesting the urinary tract. The bacteria can thus increase the pH-level of the urine to a level more comfortable to them.

If you can smell the ammonia, it is very likely for the pH-level to rise well above 7. This is a problem, because at high pH-levels in the presence of ammonia, struvite crystals can form and cause further problems in the urinary tract. Struvite crystals cause lesions and inflammatory processes, and can even block the bladder from emptying.

Sudden urinating outside the box is an indication of painful processes in the urinary tract. The cat connects pain during urinating with the place where it happens and tries to change that. Also peeing on cold surfaces happens when urinating is painful. Source of pain are all inflammatory processes, and struvite crystals are a good candidate here.

It is in any case necessary to stop the source of ammonia. Talk to your vet, soon. There are rare cases of damaged kidneys producing ammonia on their own, but those have to be checked by the vet anyway.

You can check the pH-level of the urine in advance with common testers available over the counter.


Have the vet check her sugar. Increased drinking could also be diabetes, treated with medicine and often reversed with a low carb diet. My cat has diabetes, and occasionally the urine smells very strong of ammonia. Definitely worthy of a trip to the vet


All good advice. Bottom line: Vet visit ASAP. She is in pain and if untreated, everyday her condition is almost certainly worsening.

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