Old Urine Smell in Carpet and Padding: How to Remove It for Good

Old urine smell in carpet and padding comes from dried uric acid salts and bacteria that soak past the carpet fibers into the pad and sometimes the subfloor. The reliable fix is an enzyme-based urine cleaner applied in enough volume to reach as deep as the urine went, left wet for the time on the label, then allowed to dry slowly. If the smell survives two or three thorough treatments, the padding under that spot usually needs to be cut out and replaced.

Why does old urine smell come back when the carpet gets damp?

Old urine smells stronger on humid days because moisture reactivates the dried salts and the bacteria feeding on them. When urine dries, the water evaporates and leaves uric acid crystals behind. Ordinary soaps and carpet shampoos do not dissolve those crystals well, so the spot can look clean while the source stays in place. Humidity, mopping nearby or a steam cleaner brings the odor back.

The padding makes the problem worse. Most carpet pad is foam or fiber that absorbs liquid like a sponge, and a small stain on the surface often covers a much wider wet patch underneath.

How do you find every old urine spot?

An ultraviolet (UV) flashlight in a dark room is the easiest way to find dried urine, which glows a dull yellow or green under UV light. Other things glow too, so confirm each spot by smell or by pressing a damp white paper towel on it.

• Check along walls, behind furniture and in corners, where pets often go repeatedly.
• Mark each spot with painter’s tape or chalk so you treat its full outline.
• Press on the carpet: a stiff or crunchy feel under the surface can mean dried urine in the pad.
• Lift a corner of carpet near the wall if you can, and look at the pad and subfloor for dark stains.

What is the step-by-step method for carpet and padding?

The method below works because enzymes and the bacteria in these cleaners break down the uric acid that other products leave behind.

1. Vacuum the area to remove loose hair and debris.
2. Test the enzyme cleaner on a hidden patch of carpet for color change and wait for it to dry.
3. Pour enough cleaner to soak the carpet, the pad and the area just beyond the marked outline. A light spray only treats the fibers; old urine usually needs a generous amount, as the label directs.
4. Cover the spot loosely with plastic wrap or an upturned bowl so it stays wet for the dwell time on the label, often several hours.
5. Uncover it and blot up excess liquid with towels. Do not scrub, which spreads the stain.
6. Let it dry fully, which can take a day or two. Use a fan, and keep pets off the area.
7. Sniff the spot when dry. Repeat the treatment if any odor remains.

Skip heat until the smell is gone. A steam cleaner or hot-water extractor can set urine proteins and push the odor deeper. For pet accidents specifically, our guide to removing pet urine smell from carpet and stopping repeat accidents covers training and cleaning together.

Which products should you avoid on urine stains?

Ammonia-based cleaners are the main product to avoid, because urine itself contains ammonia compounds and the scent can draw pets back to the same spot. Avoid these as well:

• Bleach on carpet, which can discolor fibers and does not remove the uric acid.
• Mixing products. Never combine bleach with ammonia, vinegar or other cleaners, because some mixtures release toxic gases. Use one product at a time and rinse with plain water before switching.
• Air fresheners and scented powders that only cover the odor for a short time.
• Heavy steam cleaning before the urine has been broken down.

Follow label directions, ventilate the room and store all cleaners away from children and pets. If someone swallows a cleaning product or gets it in the eyes, contact Poison Control at 1-800-222-1222 in the US or call emergency services.

When do you need to replace the carpet padding?

Replace the padding when the smell returns after repeated deep treatments, when the pad is soaked over a large area, or when the urine has reached the subfloor. Enzyme cleaners struggle to penetrate thick, saturated pad, and some pads hold odor no matter how much cleaner you use.

The usual repair is to pull the carpet back from the tack strip, cut out the stained section of pad, and treat the subfloor with enzyme cleaner. After it dries, seal stained plywood or wood with an odor-blocking primer, lay a new piece of pad and re-stretch the carpet. Many people hire a carpet installer for the stretching. If the carpet backing itself is stained through, the affected section of carpet may also need replacing.

Could the smell be something other than urine?

A sour or ammonia smell is usually urine, but an earthy, damp smell in carpet can point to mold from a leak or high humidity. Mold growing in padding needs its moisture source fixed, which our article on finding the source of a mold smell explains. The EPA’s mold guidance advises fixing water problems and cleaning or removing damp, moldy materials. If the whole room smells stale rather than one spot, see our guide to getting rid of a musty smell in your house.

Quick answers

Does baking soda remove old urine smell from carpet?

Baking soda absorbs some surface odor but does not break down the uric acid in the padding. It can help after an enzyme treatment has dried, vacuumed up once the smell is gone.

How long does it take to get rid of old urine smell?

One full treatment plus drying usually takes one to two days. Old or heavy stains often need two or three rounds before the odor is gone.

Can vinegar remove old urine odor?

A diluted white vinegar rinse can reduce surface odor, but it does not reliably reach urine in the pad. Never use it together with bleach or other cleaners.

Will professional carpet cleaning fix it?

Standard hot-water cleaning often does not, and can make the smell worse. Ask for a urine-specific treatment that includes subsurface extraction or pad replacement.