A recurring smell can happen when the original liquid travelled through the carpet and reached the underlay or subfloor. Cleaning the visible carpet fibres may remove the surface contamination while leaving material underneath, and moisture or humidity can allow that odour to become noticeable again. Airstep's underlay guidance specifically highlights this risk and is one reason moisture-barrier underlays are considered in homes with pets or frequent spills. If an odour keeps returning, the practical next step is to have the carpet, underlay and subfloor assessed rather than repeatedly treating only the carpet face.
