What's that smell? Household odors, diagnosed
Every smell in a house has a source, and most can be found in an afternoon. Pick what it smells like. Each guide ranks the likely causes, shows you how to tell them apart, and tells you when to stop and call someone.
Quick smell finder
| It smells like… | Usually means | Start here |
|---|---|---|
| Rotten eggs or sulfur | Gas (rule out first), sewer gas, or the water heater | Rotten-egg smell |
| Natural gas or propane | A possible leak — leave and call | Smell gas? |
| Burning plastic, or fishy | An overheating electrical part or appliance | Burning plastic smell |
| Damp basement, mildew, wet towels | Moisture and mold or mildew somewhere | Musty smell |
| Sewer or toilet | A dry trap, failed toilet seal, or blocked vent | Sewage smell |
| Cat pee or ammonia | Old pet urine, mice, or — sometimes — wiring | Cat-pee smell |
| Skunk | A skunk outside — or gas, so check that first | Skunk smell |
Browse by smell
Gas, rotten eggs & sulfur
Rule out a gas leak first, then work through sewer gas, water heaters, and the other sulfur sources.
- Smell gas in the house? Do this now
Smell natural gas or propane at home? The steps to take right now, what not to touch, who to call, and what happens after the utility arrives.
- Why your house smells like rotten eggs (and how to find it)
A rotten-egg or sulfur smell at home: rule out a gas leak first, then use the hot-vs-cold water test and drain checks to find the real source fast.
- House smells like gas, but the utility found no leak
The gas company found no leak but you still smell gas? What utilities typically check, what they don't, and the elimination order for the real source.
Burning & electrical
Hot plastic, burning dust, and fishy smells that turn out to be electrical.
- Burning plastic or electrical smell in your house
Burning plastic or electrical smell at home? When to get out and call 911, how to find the source safely, and how to tell normal furnace dust from danger.
Musty & mildew
Damp, earthy, wet-towel smells. Almost always moisture somewhere — the question is where.
- Musty smell in your house
Why your house smells musty, how to find where it's coming from in about an hour, and how to get rid of it for good — plus when it's mold and who to call.
Sewage & drains
Sewer gas from traps, vents, toilets, and lines.
- Sewer smell in your house
Sewer smell in the house or bathroom: the order to check traps, drains, toilet seals, vents, and lines — and when sewer gas means ventilate and get out.
Pets, urine & animals
Cat-pee and dog smells — including when you don't have a pet — and skunks.
- House smells like cat pee and you can't find it
Cat-pee or ammonia smell with no obvious source — or no cat? How to hunt it down with a UV light, what else smells like urine, and when it's electrical.
- House smells like dog
Why a house smells like dog even when it's clean — the fabrics, filters, and damp air that hold it — plus a room-by-room plan to get rid of it.
- Skunk smell in your house
Skunk smell inside but no skunk in sight? Rule out a gas leak first, then find whether a skunk is under the house or a drain is venting sewer gas.
Something else
No dedicated guide yet. The diagnostic covers these:
How these guides work
Each guide follows the same diagnostic order a good tradesperson would: safety first, then the most common cause, then the evidence that separates it from its look-alikes, then the cheapest test. Causes are ranked by how often they explain the smell in ordinary homes. That ranking is our judgment from trade guidance, and we label it that way rather than inventing percentages.
We don't sell air fresheners, and we don't give medical advice. If a smell comes with people feeling unwell, get fresh air first.
Describe the smell, where it is, and when it happens. You'll get likely causes and safe checks in about a minute.