Why the usual "clean it and it's gone" approach fails

Carpet is porous through multiple layers, the fibre, the backing, and the padding underneath, and urine soaks down through all three within minutes of an accident. Wiping or shampooing only the visible surface leaves residue in the padding that continues to smell, especially when humidity rises. This is the main reason a carpet spot can look and smell fine for weeks and then suddenly smell again.

Step 1, blot, don't rub

As soon as you find an accident, blot up as much liquid as possible with paper towels or a clean cloth, pressing down firmly rather than rubbing, which pushes the liquid further into the fibres and padding. Continue until the towel comes away dry.

Step 2, saturate with an enzymatic cleaner

Apply the enzymatic cleaner generously over the entire affected area, including a small margin beyond the visible stain, since urine spreads sideways under carpet more than most people expect. The product needs enough volume to reach the same depth the urine did, a light spray on top isn't enough for anything beyond a very fresh, small accident.

Step 3, give it proper contact time

Enzymatic cleaners need time for the bacterial enzymes to actually break down the uric acid and other residue, check the product label, but 10-15 minutes is a common minimum, and older or larger stains often benefit from longer, or a second application after the first has worked. Resist the urge to blot it dry too early; that cuts the treatment short.

Step 4, dry it properly

Blot up the excess cleaner once the contact time has passed, then let the area air dry fully, ideally with some airflow (a fan or open window) to prevent damp carpet padding from developing its own smell. Avoid steam cleaning or applying heat to the spot until you're confident the residue is gone, heat can permanently set any remaining stain and odour into the fibres.

For older or set-in stains

Deep, dried-in accidents from before you started using enzymatic cleaners may need two or three treatments over several days rather than one pass. If a smell persists strongly after repeated enzymatic treatment, the padding underneath may need replacing in that section, since fully saturated padding can be beyond what surface treatment can reach.