Why your house smells like rotten eggs (and how to find it)
Last reviewed · Not medical advice
Rotten eggs means sulfur: either the odorant added to natural gas and propane, or hydrogen sulfide from drains, water, or bacteria. Treat it as gas until you've ruled that out. If it's strong, sudden, or near a gas appliance, leave and call from outside. If it's faint and tied to water — one drain, or only the hot water — it's almost always a dried-out drain trap or the water heater. A two-glass test (hot vs cold) settles the water question in a minute.
Most likely causes
Ranked for this situation. Open any cause for checks and fixes.
- 1
Natural gas leak
commonAct nowNot the most frequent cause, but always the first to rule out. The odorant added to gas is designed to smell exactly like this.
Points to this:- Strongest near the stove, furnace, water heater, dryer, or gas meter
- Hissing or whistling near a line or appliance
- Smell came on suddenly and doesn't fade with ventilation
Check it, fix it, who to call
Safe checks- Do not hunt for the leak. If the smell is strong or you're unsure, leave and call from outside.
- A faint smell right at the stove: check whether a burner knob was left on without lighting. If so, turn it off and air the room — and leave and call if the smell doesn't clear quickly.
Fix- The utility (natural gas) or supplier (propane) finds and isolates the leak.
- A licensed plumber or gas fitter repairs the line or appliance connection.
DIY stops here: There is no DIY step beyond leaving and calling. Don't use soapy-water tests indoors while the smell is present.
Who fixes it: Your gas utility's emergency line
More on this - 2
Dried-out drain trap
most commonThe everyday answer when the smell is near a rarely used sink, shower, or floor drain.
Points to this:- Smell is near a guest bath, basement floor drain, unused shower, or utility sink
- Started after a trip, or in a room nobody uses
- Goes away after running water
Check it, fix it, who to call
Safe checks- Run water in every sink, tub, and shower for 30 seconds, and pour a bucket of water into floor drains.
- Flush toilets that rarely get used.
- Wait a few hours. If the smell is gone, it was a dry trap.
Fix- Run water in rarely used fixtures every couple of weeks.
- For floor drains that dry out constantly, a plumber can fit a trap primer or a trap-seal insert.
DIY stops here: If refilling the traps doesn't stop it within a day, the problem is past the trap — call a plumber.
Who fixes it: Plumber
More on this - 3
Water heater reaction (sulfur in hot water)
most commonIf only the hot water smells, this is almost certainly it.
Points to this:- Only the hot water smells; cold water from the same faucet is fine
- Worse after the heater has sat unused, or after a vacation
Check it, fix it, who to call
Safe checks- Fill one glass with hot water and one with cold, step away from the sink, and smell each.
- Check whether the smell appears at every hot tap (water heater) or just one (that fixture's drain).
Fix- Flush the water heater.
- Have a plumber replace the magnesium anode with an aluminum-zinc or powered anode.
- Ask a plumber about sanitizing the tank.
DIY stops here: Anode replacement on a gas or electric heater is usually a plumber job — you're working with gas lines or 240V and a pressurized tank.
Who fixes it: Plumber
More on this - 4
Slime in a sink drain or overflow
commonSmell sits right at one drain or the sink overflow hole.
Points to this:- Smell is right at one sink or shower, strongest with your nose at the drain
- The drain is slow
- The overflow hole under the sink rim smells when you sniff it
Check it, fix it, who to call
Safe checks- Sniff the drain opening, then the overflow hole, separately.
- Pull the pop-up stopper — it's often coated in sludge.
Fix- Clean the stopper; scrub the drain and overflow with a long brush.
- Flush with very hot water. Use an enzyme drain cleaner for ongoing buildup.
DIY stops here: If cleaning doesn't change the smell, look for a trap or vent problem.
Who fixes it: You (DIY)
More on this - 5
Hydrogen sulfide in well water
commonOnly on private wells — and both hot and cold water smell.
Points to this:- Home is on a private well
- Both hot and cold water smell, at every faucet
Check it, fix it, who to call
Safe checks- Compare hot and cold glasses at several taps; have the well water tested.
Fix- Water treatment, e.g. aeration, oxidizing filters, or chlorination, sized to the test results.
DIY stops here: Choose treatment from a lab test, not a guess.
Who fixes it: Plumber
More on this - 6
Blocked or damaged plumbing vent
less commonWithin daysComes with gurgling drains.
Points to this:- Drains gurgle or bubble, especially when a toilet flushes
- Water levels in toilet bowls drop or fluctuate
- Smell in several rooms, worse on windy days
Check it, fix it, who to call
Safe checks- Flush a toilet and listen at nearby sinks and tubs for gurgling.
- Look at the roof vent from the ground with binoculars for a nest or debris (don't climb onto the roof).
Fix- A plumber clears the vent stack or repairs a cracked or disconnected vent pipe.
DIY stops here: Roof work and snaking vents are a job for a plumber.
Who fixes it: Plumber
More on this - 7
Propane leak
less commonAct nowPropane homes only; collects low to the floor.
Points to this:- Home or appliance runs on a propane tank
- Smell strongest low down or near the tank, regulator, or an appliance
Check it, fix it, who to call
Safe checks- Leave, then close the tank's main valve (clockwise) only if you can reach it safely.
- Call your propane supplier or 911 from a safe distance.
Fix- Your supplier or a qualified technician leak-tests and repairs the system before relighting.
DIY stops here: Beyond closing the tank valve on the way out, nothing — don't relight pilots yourself after a leak.
Who fixes it: Your propane supplier
More on this - 8
Dead animal in a wall, attic, or crawlspace
less commonMore rotten-sweet than pure sulfur, concentrated at one wall.
Points to this:- Rotten or sickly-sweet smell concentrated on one wall or ceiling area
- Flies appearing indoors; recent rodent activity
Check it, fix it, who to call
Safe checks- Sniff along walls to find the strongest spot; check attics, crawlspaces, and behind appliances.
Fix- Remove the animal if you can reach it (wear gloves).
- Otherwise pest control can locate and remove it; ventilate while it fades.
DIY stops here: Opening walls or entering attics with insulation: pest control or a handyman.
Who fixes it: Pest control
More on this - 9
Overcharging lead-acid battery
rareSame dayNear a UPS, sump-backup battery, or charger in the garage.
Points to this:- Smell near a battery backup unit, battery charger, or in the garage
- Battery case swollen or hot
Check it, fix it, who to call
Safe checks- Find any lead-acid batteries in the house; feel the case from a distance for heat (don't touch a swollen one).
Fix- Disconnect the charger at the outlet if it's safe to reach.
- Replace the battery and have the charger checked.
DIY stops here: A hot, swollen, or hissing battery: ventilate, keep away, and call the fire department if it's smoking.
Who fixes it: Licensed electrician
More on this
How we rank causes: by how often each one explains this smell in ordinary homes, according to plumbing, HVAC, electrical, and building-science guidance, adjusted for the context on this page. The labels are judgments, not measured statistics. Anything dangerous that can't be ruled out (gas, fire, electrical) is covered in the safety box at the top of the page, whatever its rank.
Which one is it?
| Where / when you smell it | Likely source | Urgency |
|---|---|---|
| Near the stove, furnace, water heater, or meter — strong or sudden | Gas leak | Leave and call now |
| Only from hot water, at every hot tap | Water heater | Routine |
| Hot and cold water, every tap, private well | Well water sulfur | Routine |
| One unused bathroom or basement floor drain | Dry drain trap | Routine |
| Right at one sink drain or overflow hole | Drain slime | Routine |
| Near a battery backup or charger | Overcharging battery | Urgent |
| One wall, rotten-sweet, flies around | Dead animal | Routine |
Narrow it down
Answer in order. Stop at the first yes.
- 1Is it strong, sudden, near a gas appliance or line — or is anyone feeling unwell?Yes → Stop here. Leave and call your gas utility or 911 from outside. Go thereNo → Keep going, but stop and leave if it gets stronger.
- 2Does it only show up when water runs?Yes → Do the two-glass test below to split hot water, cold water, and drains.No → Keep going.
- 3Is it strongest at one drain or in a room nobody uses?Yes → Refill the trap and clean the drain — see the sewage page if it persists. Go thereNo → Keep going.
- 4Did the gas utility already check and find nothing?Yes → Work the elimination list for cleared homes. Go there
Safe checks you can do yourself
In the order that finds the source fastest.
- 1
Rule out gas first
If the smell is strong, sudden, or near anything that burns gas, don't investigate — follow the safety steps above. When unsure, report it — gas-safety guidance is to always call rather than assume.
- 2
Two-glass test (hot vs cold)
Fill one glass from the hot tap and one from the cold tap. Carry them away from the sink and smell each. Hot only → water heater. Both → the water supply (common on wells). Neither, but the sink smells → the drain, not the water.
- 3
Refill every trap
Run water for 30 seconds in every sink, tub, and shower, flush rarely used toilets, and pour a bucket of water into basement floor drains. Give it a few hours.
- 4
Sniff the drain and overflow separately
Put your nose at the drain opening, then at the overflow hole under the sink rim. Slime in either one smells like sulfur or sewage without any sewer problem.
- 5
Check batteries and the garage
Look for lead-acid batteries — UPS units, sump-pump backups, golf carts, or a car on a charger. A hot or swollen case with a sulfur smell means unplug the charger if it's safe, ventilate, and keep away.
Why gas and drains smell the same
Natural gas and propane are odorized with mercaptan, a sulfur compound chosen because it smells like rotten eggs. Drains, sewers, and some water supplies produce hydrogen sulfide, another sulfur compound with nearly the same smell. Your nose can't reliably tell them apart. That's why location and timing — near a gas appliance or near water — matter more than the smell itself.
Fixing a smelly water heater
The smell comes from bacteria in the tank reacting with the anode rod, a metal rod that protects the tank from corrosion. Flushing the tank helps for a while. The lasting fix is usually swapping the standard magnesium anode for an aluminum-zinc or powered anode, and sometimes sanitizing the tank. Because it means working on a pressurized tank connected to gas or 240V power, most people have a plumber do it. Don't remove the anode without replacing it — it protects the tank.
When DIY stops
- Any chance it's gas: leaving and calling is the only DIY step.
- Anode rod replacement or tank sanitizing — a plumber job for most people.
- Refilled traps and cleaned drains didn't help within a day.
- A hot, swollen, or hissing battery.
Who to call
- Your gas utility's emergency line
Any time you suspect gas. Call from outside the house.
Checks for natural gas leaks. Call its emergency number, not the billing line.
- Your propane supplier
You heat or cook with propane and suspect a leak.
Checks propane tanks, lines, and appliances for leaks.
- Plumber
Hot water smells, traps keep drying out, or drains gurgle.
Drains, traps, toilets, vents, water heaters, and leaking supply lines.
- Pest control
The smell is rotten-sweet at one wall and you suspect a dead animal.
Finds and removes mice and rats, and seals entry points.
- Licensed electrician
A battery backup or charger is overheating.
Outlets, switches, wiring, panels, and light fixtures.
Answer a few questions about where and when you smell it. You'll get the causes ranked for your situation.
Frequently asked questions
Should I call the gas company for a rotten egg smell?
Yes, if there's any chance it's gas — especially if it's strong, sudden, or near a gas appliance. Call from outside. If it turns out to be a drain or the water heater, nothing is lost.
Why does only my hot water smell like rotten eggs?
Bacteria in the water heater react with the anode rod and make hydrogen sulfide. Flushing the tank helps temporarily. Replacing the anode with a different type usually fixes it.
Why does my bathroom smell like rotten eggs?
Most often a dry trap in a shower, tub, or sink that isn't used, or slime in the drain and overflow. Run the water and clean the drain. If it stays, check the toilet seal and the vent.
Can a rotten egg smell come and go?
Yes. Dry traps refill when someone uses the fixture, water heater smells follow hot-water use, and blocked vents depend on wind and flushing. A gas smell that comes and goes still needs a call to the utility.
Is there a gas detector I can use?
Plug-in natural gas and propane alarms exist and can be a useful backup, especially for people with a weak sense of smell. They don't replace calling the utility when you smell gas.
Related smells
Sources
- Using Natural Gas Safely — American Gas Association
- Carbon Monoxide Information Center — U.S. CPSC