Why Does My House Smell Like Rotten Eggs?
If there is any chance it is gas, act on that first. Natural gas has no odor of its own, and Connecticut's Public Utilities Regulatory Authority says gas companies add a chemical called mercaptan to give it its distinctive rotten egg smell. Federal pipeline safety guidance from PHMSA says to leave the area on foot immediately, not to try to find the source of the odor or leak, and to call 911 from a safe location and then notify the pipeline company.
The other common source is hydrogen sulfide, a flammable, colorless gas that ATSDR says smells like rotten eggs and is often called sewer gas. The Minnesota Department of Health says hydrogen sulfide can give well water a rotten egg taste or odor, and that it can occur naturally, be produced by sulfur bacteria in the groundwater, well or plumbing system, or be produced by sulfur bacteria or chemical reactions inside water heaters.
ATSDR says people can usually smell hydrogen sulfide at very low levels, 0.0005 to 0.3 parts per million, but lose the ability to smell it after about 2 to 15 minutes of exposure at about 100 ppm, which makes the odor an ineffective warning. It says longer-term exposure around 10 ppm or less can cause eye irritation, headache and fatigue, and that very high levels above 500 ppm can cause sudden unconsciousness or death.
Sources checked September 15, 2026. Every point below links the page it came from.
The sources behind this answer
- Government sourceATSDR describes hydrogen sulfide as a flammable, colorless gas that smells like rotten eggs, is often called sewer gas, and can usually be smelled at 0.0005 to 0.3 parts per million in air. ATSDR, CDC ↗
- Government sourceATSDR says hydrogen sulfide above 500 ppm can cause sudden unconsciousness or death, and longer-term exposure around 10 ppm or less can cause eye irritation, headache and fatigue. ATSDR, CDC ↗
- Government sourceATSDR says people lose the ability to smell hydrogen sulfide after about 2 to 15 minutes at about 100 ppm, which makes the odor an ineffective hazard warning. ATSDR, CDC ↗
- Government sourceThe Minnesota Department of Health says hydrogen sulfide can give well water a rotten egg taste or odor and can occur naturally, come from sulfur bacteria in groundwater, wells or plumbing, or form inside water heaters. Minnesota Department of Health ↗
- Government sourceConnecticut's Public Utilities Regulatory Authority says natural gas has no odor, gas companies add mercaptan to give it a rotten egg smell, and all natural gas and propane pipeline gas in Connecticut is odorized. Connecticut Public Utilities Regulatory Authority ↗
- Government sourcePHMSA says that for a suspected pipeline leak you should leave the area by foot immediately, not try to locate the source, and call 911 from a safe location before notifying the pipeline company. US Pipeline and Hazardous Materials Safety Administration, via web.archive.org ↗
Sources checked September 15, 2026. A brand statement is the company’s own claim, which we report but have not verified. Our grades are model-based estimates, not lab tests.