How to get cat pee out of carpet
If you’re reading this blog post, I know what kind of day you’re having.
Happily, this is one of those life problems that can actually be solved!
I’ll start by explaining why cat pee smells so bad and is so hard to remove. Once you understand, you can use that scientific knowledge to attack the problem of cleaning it up.
It’s helpful to have the right tools on hand for the job. Ideally, you want to have three items in your cupboard, ready to go, before you ever have to clean cat pee out of a rug:
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- A UV light (like this one by DARKBEAM) to help you identify the location of the stain;
- A clean white cloth for dabbing. An old terrycloth hand towel or tea towel works well, as do absorbent paper towels; and
- An enzymatic cleaner designed to work with pet stains and on carpets, such as Angry Orange, Simple Green, or Nature’s Miracle.
Why does cat pee smell so bad?
The smell of cat urine is particularly offensive to our sense of smell. Urine isn’t anyone’s favorite scent, but cat urine takes it to another level. Once you’ve smelled cat pee, you can’t unsmell it, and you will never forget that odor.
Cat pee is just pee
Urine is urine is urine. Urine from any animal is just the “leftovers” from metabolism – the process by which a body converts what it eats and drinks into energy. Blood vessels carry the leftovers – urea, uric acid, chloride, sodium, potassium, creatinine and other stuff – to the kidneys, and the kidneys filter these waste products out. Urine is a mixture of these chemicals and some water, which gets stored in the bladder and will exit the body through the urethra.
But cat pee is smellier than other animals’ pee
Cat urine seems smellier than urine from other animals, though. There are two reasons why:
1) Cat urine is more concentrated than the urine of other animals.
The ancestors of our house cats were desert animals who had to learn how to survive in very dry climates. Their bodies were designed to work with as little water as possible. Cats are obligate carnivores, meaning they must eat meat to survive, and so a cat’s body probably expects to get most of the moisture that it needs from the juices in prey.
Why would a desert-animal’s pee smell stronger than another animal’s? A cat’s kidneys were designed to “wring” as much water as possible out of the urine. Cats' kidneys have a very long “loop of Henle” to help them be extra stingy with water. Consequently, the smelly waste products in cat urine are not well diluted. We humans, by comparison, have a shorter loop of Henle, and thus our urine is not nearly as concentrated (or smelly).
It might be helpful to read this post for more information about cats and their sometimes-uncomfortable relationship with drinking water: “Why won’t my cat drink out of her bowl?”
2) Cats use chemicals in urine to communicate.
Dogs live cooperatively, and employ a wide range of tactics to communicate with each other and avoid conflicts within their social group.
Cats are also social animals, but they’re not like dogs. They tend to hunt and eat alone, and sometimes sleep alone. To avoid conflict with other cats, they communicate with scent. Scent allows a cat to send a message to other cats without having to get too close to them. Scent, in the form of pee on a tree trunk, for example, can provide important information to passing cats. Scent communication means that two cats never have to interact face to face to “talk” to each other.
Male cats that have not been neutered have more to say to the world, and thus their urine contains additional odor-causing compounds. An intact male cat’s urine will contain pheromones and testosterone that say “come hither” to the ladies in the area, and “stay away” to the guys.
Unneutered male cat pee also contains an amino acid called “felinine.” Felinine starts out odorless, but breaks down at room temperature and starts to smell. It contains sulfur, which is the stink we associate with rotten eggs and sewer gases.
Cat urine smells worse as it starts to decompose
Cat pee starts out smellier than other pee (because it is more concentrated, and because it contains extra chemicals for communication), and becomes even smellier over time. Bacteria start to decompose the urea in urine, producing ammonia in the process. Ammonia is what gives cat pee that "old cat pee" smell.
Urea smells, but luckily it’s water soluble. You can get rid of decomposing urea smell with ordinary cleansers and water.
Many websites recommend cleaning up cat pee with homemade cleaning solutions, made with water, vinegar, baking soda, hydrogen peroxide, or detergents. And they do seem to work – initially.
Any cat-pee removal solution needs to address uric acid
The problem is that homemade cleaning solutions don't address the bigger problem: uric acid.
Uric acid is another component of urine and it's not so easy to get rid of. Unlike urea, uric acid is not water soluble. It tends to bind tightly to whatever surface it’s “applied” to, including the carpet, the padding beneath, and the wooden subfloor.
Uric acid is actually a salt crystal. Exposing uric acid to moisture actually causes the uric acid to recrystallize. So, when you try to clean up cat urine with ordinary water-based solutions, you’re actually reactivating those uric acid crystals. No wonder that pee-smell keeps coming back!
Enzymes are the answer
You can’t just lift the uric acid out of your carpet or wash it out.
It will eventually decompose on its own, but according to one source, cat urine has a half-life of six years! That means it would only be half-decomposed in six years’ time. Gross!
The only way to break the chemical bond between the uric acid and your carpet is to break up the uric acid itself – in other words, to speed up the natural decomposition process.
Enter enzymes! Enzymes are proteins (usually) that have the power to start or speed up a chemical reaction.
Specific enzymes work on specific proteins. You need the right enzymes to break down the uric acid in your carpet. These enzymes are called ureases.
Ureases will take the uric acid in your carpet and break it down into its components: carbon dioxide and ammonia. The carbon dioxide and ammonia, once released, will just evaporate. Pee problem solved!
Step by step instructions for getting cat urine out of carpeting
Step One: Find the pee
Just because you can smell urine, doesn’t mean you know exactly where it is. In fact, the uric acid crystals are invisible.
Your cats can smell the urine even better than you. Urine smell is a signal to your cat to pee in that exact same spot again. If you don't want your cat to pee in that same spot for the rest of his life, you must find every droplet of pee and break up the uric acid crystals in that spot with enzymes.
If you can’t see the pee, how can you find it? Luckily, there's a trick. You can "see" all the pee you can't see with your naked eye with a black light, also called an ultraviolet light or UV light.
What is UV light? Do you remember learning to name all the visible colors of the rainbow in elementary school? Red, orange, yellow, green, blue, indigo, and violet, in that order. Well, beyond violet is ultraviolet. We can’t see ultraviolet, but we can create light waves with an ultraviolet frequency.
Pet pee glows when exposed to black light, even if it’s dried, and even if it’s old. You can buy a UV flashlight, like this one by DARKBEAM, which emits a wavelength of 365 nanometers – perfect for finding pet urine (385 nm flashlights work well, too). Note that there are many UV lights on the market that emit wavelengths of 395 or 400 nanometers, which are fine for other applications, but work less well in exposing urine.
To use the UV flashlight, turn off the lights in the room and shut the shades, or wait until nighttime. It’s easier to see the cat pee glow under the UV light in a dark room.
Shine the light everywhere, not just where you think there might be pee. Look on vertical surfaces, especially around doors and windows where cats are more likely to spray. Look for individual droplets, and also for drops that run down the wall. On horizontal surfaces, look for yellow splatter marks.
Here’s a helpful video that shows how cat urine glows under a black light.
Step Two: Mop up any fresh urine
If the urine puddle is still wet, absorb as much as you can with a highly absorbent white cotton cloth (like an old tea towel or terrycloth hand towel) or good quality paper towels. Keep pressing and dabbing, being careful not to rub, which can damage carpet fibers, and drive the stain even deeper, until your cloth is no longer absorbing additional liquid.
If the pee is old or already dried, skip this step.
Step Three: Treat the spot with an enzymatic cleaner
There are a number of excellent products on the market, but be sure to choose one that states that it contains enzymes on the container. You don't want all of your efforts to simply reactivate your uric acid crystals. You want to destroy them.
Note that each of these brands sells more than one formulation of their products. Some formulations come ready-to-go and can be sprayed on the stain directly; others need to be diluted in water first.
Read and follow the instructions carefully. Some companies recommend spraying or soaking the stain and waiting for a certain period of time before blotting. Other products should be applied and left to dry.
You may need to repeat the application of the stain remover more than once for old or stubborn stains.
When you are satisfied with the results and your carpet has dried completely, vacuum to fluff the carpet fibers back up.
Note that enzymatic cleaners themselves break down over time. Don't buy too big of a bottle all at once, and be sure to replace it as frequently as the manufacturer recommends.
The best way to keep carpets clean
The best way to keep carpets clean is to have cats pee where they are supposed to pee.
Cats who pee anywhere but their designated litter boxes may do so for a number of reasons. I’ve addressed these concerns in two different blog posts. This one is for cat guardians who are dealing with a cat who is spraying urine:
This one is for cat guardians who have cats who pee just outside the box, on clothes left on the floor, or on other horizontal surfaces in the house:
Note that it may take some work to get to the bottom of why your cats are peeing on your carpet instead of in their litter box, but it will probably be less work overall than the chore of removing urine from your carpets for the foreseeable future.
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 “Can You Boost Your Metabolism?” Mayo Clinic, Mayo Foundation for Medical Education and Research, 10 Nov. 2020, www.mayoclinic.org/healthy-lifestyle/weight-loss/in-depth/metabolism/art-20046508.
 Boundless. “Boundless Anatomy and Physiology.” Lumen, courses.lumenlearning.com/boundless-ap/chapter/urine/.
 Lee, Dr. Justine. “Why Does Cat Pee Stink Worse than DOG Pee?” Dr. Justine Lee, 18 Oct. 2018, drjustinelee.com/why-does-cat-pee-stink-worse-than-dog-pee-dr-justine-lee-dacvecc-dabt-board-certified-veterinary-specialist/.
 “Breaking the Cycle: The Chemistry of Pet Urine Odor Removal.” Triangle Legacy Flood Restoration & Carpet Cleaning, 26 Nov. 2019, www.atrianglelegacy.com/breaking-cycle-chemistry-pet-urine-odor-removal/.
 Gulbranson, Melissa. “The #1 Way to Fight Urine Odor: Oxyfresh.” Oxyfresh Pet Health Blog, 21 July 2020, pethealth.oxyfresh.com/pet-health/1-way-fight-urine-odor/.
 Munkevica, Signe, and Maris Munkevics. “How to Find Pet Stains with a Black Light.” Pet, Pet Happy LLC., 25 Nov. 2020, pet-happy.com/how-to-find-cat-urine-stains-with-a-black-light/.