Why Does My House Smell Like Rotten Eggs?

Natural gas is odorless in its natural state. Utility companies add a chemical called mercaptan that smells like rotten eggs specifically so you can detect leaks. If you smell rotten eggs and your home uses natural gas (for the furnace, stove, water heater, or dryer), treat it as a gas leak until proven otherwise.

What to do immediately:

Do NOT turn on or off any lights, appliances, or electronics. A spark can ignite the gas.

Do NOT use your phone inside the house.

Open windows and doors as you leave.

Get everyone (including pets) out of the house.

Once outside, call your gas utility's emergency number (printed on your bill) or 911. The gas company will send someone out for free to check for leaks, usually within an hour.

Signs it's a gas leak: the smell is strongest near gas appliances or the gas meter, the smell appeared suddenly, you hear a hissing sound near a gas line, or plants near an outdoor gas line are dying or discolored.

Don't talk yourself out of calling. False alarms happen and the gas company doesn't care. They'd rather check and find nothing than have an explosion.

If the rotten egg smell is only in your hot water (not cold), the most likely cause is a chemical reaction between the anode rod in your water heater and bacteria in the tank.

The anode rod (usually magnesium) reacts with sulfate-reducing bacteria that naturally exist in some water supplies. This reaction produces hydrogen sulfide gas... the actual compound that smells like rotten eggs. The smell comes out when you run hot water.

How to confirm: run only the hot water at a faucet and smell it. Then run only the cold water. If the smell is only in the hot water, it's the water heater.

Fixes (from easiest to most involved):

1. Flush the water heater tank to remove bacteria and sediment. Hook up a garden hose to the drain valve and flush until the water runs clear.

2. Replace the magnesium anode rod with an aluminum/zinc anode rod. Aluminum/zinc rods are less reactive with sulfate-reducing bacteria and usually solve the problem. This is a $20-$30 part and a DIY job.

3. Temporarily increase the water heater temperature to 160-degrees F for a few hours to kill the bacteria, then lower it back to 120-degrees F. Warning: 160-degree water can scald. Don't use hot water during this process.

4. If nothing else works, have a plumber install a powered anode rod ($100-$200) that uses electrical current instead of sacrificial metal.

Every drain in your house (sinks, showers, floor drains, toilets) has a P-trap... a U-shaped section of pipe that holds water. This water seal blocks sewer gas from coming up through the drain into your house.

When a drain isn't used for a while, the water in the trap evaporates. Once the trap is dry, sewer gas (which contains hydrogen sulfide... rotten eggs) rises freely into the room.

Common culprits: guest bathroom drains that haven't been used in weeks, basement floor drains, utility sink drains, and the drain in a rarely used shower.

The fix: run water in every drain for 15-20 seconds. That's it. The water refills the trap and blocks the gas.

For drains that rarely get used (basement floor drains especially), pour a small amount of mineral oil or RV antifreeze into the drain after running water. These evaporate much more slowly than water and keep the trap sealed for months.

If the smell returns quickly after running water, the trap might be damaged, improperly installed, or missing entirely. Call a plumber to inspect.

If the rotten egg smell is persistent, present in multiple rooms, and doesn't go away after checking drain traps... the issue might be in your sewer system.

A blocked or damaged sewer vent pipe (the pipe that goes through your roof to vent sewer gas outside) can redirect gas back into the house. Vent pipes can get clogged by bird nests, leaves, ice in winter, or even dead animals. A cracked vent pipe in the attic or wall cavity leaks sewer gas directly into your living space.

Signs of a vent problem: gurgling sounds when drains empty, slow drains throughout the house (not just one), and the smell is worse when it's windy outside.

A damaged or collapsed sewer line can also produce the smell, especially if it's leaking under or near the foundation. This is more serious and requires a plumber with a sewer camera to diagnose.

Sewer problems aren't DIY territory. Call a plumber. They'll typically start with a camera inspection of the sewer line ($100-$300) and check the vent pipe from the roof.

If you're on well water, the rotten egg smell might simply be your water. Some groundwater contains naturally occurring hydrogen sulfide from decaying organic matter or sulfur-bearing rock formations.

The tipoff: the smell is in both hot AND cold water, and it's been there since you moved in (or since a change in the water table).

Solutions for sulfur in well water:

Activated carbon filter: removes low levels of hydrogen sulfide. Whole-house carbon filters run $500-$1,500 installed.

Oxidizing filter (manganese greensand or birm): effective for moderate sulfur levels. $1,000-$2,500 installed.

Chlorine injection system: for high sulfur levels. Injects chlorine to oxidize the hydrogen sulfide, then a carbon filter removes the chlorine. $1,500-$3,000 installed.

Aeration system: introduces air to the water to off-gas the hydrogen sulfide before it enters the house. $2,000-$4,000 installed.

Get a water test first ($50-$150 from a certified lab) to determine the hydrogen sulfide concentration. The right treatment depends on the level.

This one is unpleasant but more common than you'd think. A mouse, rat, squirrel, or bird that died in a wall cavity, crawl space, or attic produces a sulfur-like smell as it decomposes. The smell can be similar to rotten eggs, though it usually has more of a "death" quality to it... sweet and heavy rather than sharp.

Signs it's a dead animal: the smell is localized to one area, it appeared suddenly, and it gets worse over several days before slowly improving over 2-3 weeks as decomposition completes.

If you can locate and access the carcass, removing it eliminates the smell faster. If it's in a wall cavity... you have a decision to make. Cutting into the wall to remove it works but creates a repair project. Alternatively, you can wait it out (2-4 weeks for a small animal to fully decompose) and use odor-neutralizing products to manage the smell in the meantime.

To prevent recurrence: seal entry points where animals can get into the house. Common entry points include gaps around pipes, dryer vents, attic soffits, and foundation cracks.

Systematic troubleshooting:

1. Is the smell near gas appliances or the gas meter? Call the gas company. Don't investigate further until they clear it.

2. Is the smell only when running hot water? It's the water heater anode rod. Flush the tank and consider replacing the rod.

3. Is the smell coming from a specific drain? Run water in that drain for 30 seconds. If the smell stops... it was a dry trap. Problem solved.

4. Is the smell in both hot and cold water? Get your water tested for hydrogen sulfide, especially if you're on a well.

5. Is the smell persistent, present in multiple rooms, and not associated with water? Check for sewer vent issues or a dead animal.

6. Is the smell only outside near the foundation or yard? Could be a sewer line leak or a natural gas line issue underground.

When in doubt, start with the gas company (free leak check) and work your way down the list. Better safe than sorry when hydrogen sulfide and natural gas are on the table.