What Is That Lingering Smell in My Home? A Diagnostic Guide

There's no single cause for a lingering smell — it depends entirely on the smell's character and where it's strongest. A sickly-sweet, rotting odor localized to one spot points to a dead animal; a sharp, acrid smell in a closet or along a baseboard points to rodent urine; musty and earthy points to mold or moisture; rotten-egg points to either a dry drain trap or, less commonly but seriously, a gas leak; and anything hot, burning, or fishy-plastic should be treated as a possible electrical hazard immediately. Two of those last few are genuine emergencies, not diagnostic puzzles: if the smell is burning/hot-plastic or a gassy rotten-egg odor, skip the triage below and go straight to the safety guidance. Carbon monoxide is never the smell itself — it's odorless — so a CO alarm, not your nose, is the only warning for that hazard.

"There's a smell in my house and I can't figure out what it is" is the most common way people land here — and it's the right instinct, because a smell that won't go away is a symptom, not a diagnosis on its own. This page doesn't converge on one answer. Its job is to ask the fastest discriminating questions — is it sharp or sweet, rotten or musty, tied to heat or an outlet, worst in one room or everywhere the air moves — and route you straight to the specific page (or the specific trade) that matches.