Why does new carpet smell, and how long does it last?

New carpet has a mild odour from manufacturing residues and the adhesives used in its backing, sometimes called new-carpet smell. It is normal, and it fades faster with fresh air moving through the room; opening windows for a few days after installation, where the weather allows it, clears most of it. If a smell is still noticeable after a week or two, or if it is stronger than a faint new-material scent, tell us so we can look at the underpad and the subfloor rather than assume it will settle on its own.