Why Is My House Smelling Like Rotten Eggs?

Reviewed 2026-07-30 · How we research

Most likely causes of a rotten eggs smell, ranked

1. 1. Natural gas or propane leak (mercaptan odorant)

   Must be ruled out first, every time

   Utilities odorize gas specifically so a leak smells like rotten eggs at roughly 1% concentration in air — well below the 5% lower explosive limit. A smell that is strongest near the range, dryer, water heater, furnace or meter, or that is present throughout the house, is a gas leak until a professional says otherwise.

   10-minute self-test: Do not test. Leave and call the gas utility. Their emergency response is free. Everything else on this page waits until they clear the house.

2. 2. Sulfate-reducing bacteria in the water heater

   Most common non-emergency cause

   The magnesium anode rod that protects your tank from corrosion also creates conditions for sulfate-reducing bacteria to produce hydrogen sulfide, especially in well water and in tanks kept below 120°F. The signature is unmistakable: the smell appears only when you run hot water. Swapping to an aluminum-zinc anode rod usually solves it permanently.

   10-minute self-test: Run cold water into a glass, step outside, and smell it. Then do the same with hot water. Smell in hot only means the water heater. Smell in both means the water supply. Smell in neither means it is coming from the air, not the plumbing.

3. 3. Sewer gas from a dry trap or failed seal

   Very common

   Sewer gas is largely hydrogen sulfide and methane. A dried P-trap in an unused drain, a failed toilet wax ring, or a blocked vent stack all let it in. The smell tends to be strongest near a specific drain or at floor level in one bathroom.

   10-minute self-test: Pour two cups of water down every unused drain, including basement floor drains. Rock the toilet to check for wax ring failure. If the smell clears within an hour, it was a dry trap.

4. 4. Sulfur in a private well

   Common on well water, essentially never on municipal

   Groundwater passing through shale or sandstone can carry dissolved hydrogen sulfide, along with iron and manganese. Then both hot and cold water smell. Concentrations above about 1 mg/L are noticeable; above 5 mg/L it is corrosive to plumbing and unpleasant to bathe in.

   10-minute self-test: Run an outdoor spigot upstream of the water heater for two minutes and smell the water. Odor there means the well or the incoming supply. Order a water test — many county health departments do them cheaply.

5. 5. A dead animal decomposing in a wall or duct

   Occasional, unmistakable once it peaks

   A rodent that dies in a wall cavity produces a mix of sulfur compounds and cadaverine. The smell usually builds over 3–5 days, peaks around day 10, and fades over 2–4 weeks depending on temperature and size.

   10-minute self-test: Walk the house slowly with your nose 12 inches from the wall and locate the strongest point. Look for flies gathering at one spot on a wall or ceiling — they find it before you do.

What it costs to fix a rotten eggs smell

DIY fixes for a rotten eggs smell

• Swap the water heater anode rod

  Shut off power or gas and the cold supply, drain a few gallons, and replace the magnesium rod with an aluminum-zinc rod. A $40 part and an impact wrench solve most hot-water sulfur smells for years.

• Raise the water heater temperature to 140°F temporarily

  Sulfate-reducing bacteria are killed at that temperature. Run every hot tap for several minutes to flush the lines, then return the setting to 120°F. Warning: 140°F water scalds in about 5 seconds, so restore the setting before normal use and consider anti-scald valves if you have children.

• Water every trap monthly

  Two cups per unused drain, plus mineral oil in floor drains. Costs nothing and prevents the most common sewer-gas complaint.

• Shock chlorinate a well

  For a sulfur-smelling well, standard shock chlorination often knocks the bacteria back for months. Follow your county health department procedure; do not improvise concentrations.

• Locate a dead animal with flies, not guesswork

  Blow flies cluster within a foot of the carcass. Cut a small drywall access hole at that point — it is a $20 patch versus weeks of smell.

• Install a low-level CO alarm anyway

  If a gas appliance is producing sulfur smells or yellow flames, it may also be producing CO. Put a listed alarm outside every sleeping area.

Where homeowners waste money on a rotten eggs smell

• A whole-house carbon filter for high-sulfur well water. It saturates quickly and becomes a smell source itself. Oxidize first, then filter.
• Replacing an entire water heater for a smell that a $40 anode rod fixes.
• Air fresheners while a gas leak is unresolved.
• Odor 'bombs' for a dead animal in a wall. Remove the carcass; nothing else works.

When to call a gas utility, plumber or water treatment specialist about a rotten eggs smell

Why Is My House Smelling Like Rotten Eggs — questions homeowners ask

Sources used for a rotten eggs smell

• US EPA — secondary drinking water standards (hydrogen sulfide)
• NIOSH — hydrogen sulfide exposure and IDLH values
• PHMSA — natural gas odorization requirements
• Water Systems Council — hydrogen sulfide in private wells