Sewer gas can make you sick, but serious harm from brief exposure is rare
Sewer gas is not when ready life-threatening in the small amounts most people encounter in their homes. A whiff from a backed-up drain or broken vent pipe will cause discomfort — nausea, headache, dizziness — but you will recover once you leave the area. The real risk comes from prolonged or heavy exposure, which can damage your respiratory system and, in extreme cases, cause loss of consciousness or death. Workers in sewers and septic tanks face this danger regularly; homeowners almost never do.
The gases in sewer lines are a mix of hydrogen sulfide (the rotten-egg smell), methane, ammonia, and carbon dioxide. Hydrogen sulfide is the main culprit. At low concentrations — what you smell in your bathroom — it irritates your eyes, nose, and throat. At higher concentrations, it can paralyze your sense of smell, so you stop noticing it even as exposure worsens. This is dangerous because you lose your warning signal.
Key Takeaways
- Brief exposure to sewer gas causes temporary discomfort like headaches and nausea, but serious injury from household levels is uncommon.
- Hydrogen sulfide, the main component, becomes dangerous at concentrations much higher than what leaks into homes through drains or vents.
- Prolonged exposure in poorly ventilated spaces — basements, crawl spaces, or enclosed areas near a break — poses real respiratory risk.
- Infants, elderly people, and those with asthma or lung disease face higher risk from even moderate sewer gas exposure.
- The smell itself is your best early warning; if you notice it, open windows and find the source rather than assume it will pass.
When sewer gas exposure becomes a health problem
Sewer gas becomes genuinely harmful when you breathe it in a confined space for hours or days. A basement with a cracked sewer line, a crawl space with a backed-up drain, or a bathroom with a broken vent stack can accumulate gas to levels that cause real damage. Symptoms of moderate exposure include persistent headache, dizziness, fatigue, and nausea that does not go away after you step outside. Some people report eye and throat irritation that lasts for days.
At higher concentrations — the kind found in sewers themselves, not homes — hydrogen sulfide can cause fluid buildup in the lungs, loss of consciousness, and death. But reaching those levels in a house requires either a major structural failure (a completely broken sewer line in a sealed basement) or a workplace accident (entering a septic tank without ventilation). If you smell sewer gas regularly in your home, the problem is a leak or vent failure, not a concentration that will kill you. The real issue is that you should not have to tolerate it, and the source needs repair.
Who is at higher risk from sewer gas
Infants and young children are more vulnerable because their lungs are still developing and they breathe more air per pound of body weight than adults. Elderly people and anyone with asthma, emphysema, or chronic bronchitis face greater risk because their respiratory systems are already compromised. Pregnant women may also be more sensitive, though research on this is limited.
If you have a household member in one of these groups and you notice sewer gas smell, treat it as a priority repair rather than a minor inconvenience. Even low-level chronic exposure can worsen existing lung conditions. Children with asthma exposed to sewer gas may experience more frequent attacks. For these households, the threshold for "this is a problem" is lower than for a healthy adult.
Symptoms of sewer gas exposure
Short-term exposure — a few minutes to an hour — typically causes headache, nausea, dizziness, and eye or throat irritation. These symptoms usually fade within an hour of leaving the area. Some people also report a temporary loss of appetite or mild stomach upset.
Longer exposure, over hours or days, can cause fatigue, persistent headache, and respiratory irritation that lingers even after you leave the space. In rare cases, people report difficulty breathing or chest tightness. If symptoms persist after you have opened windows and left the area, or if you develop difficulty breathing, seek medical attention and tell the doctor you were exposed to sewer gas.
One dangerous aspect of hydrogen sulfide is that your sense of smell adapts to it. After 15 minutes of exposure, you may stop noticing the smell even though the gas is still present. This is called olfactory adaptation. It means you cannot rely on your nose to tell you when exposure is becoming unsafe. If you smell sewer gas, assume it is present at levels that warrant investigation, not something to ignore.
Common sources of sewer gas in homes
A dry or blocked P-trap — the U-shaped pipe under sinks and drains — is the most common source. The trap holds water that seals out sewer gas. If a drain has not been used in weeks, the water evaporates and the seal breaks. If the drain is blocked, pressure can build and force gas back up through the pipe.
A broken or missing vent stack — the pipe that runs from your sewer line up through the roof — allows gas to back up into the house instead of venting to the outside. Damage from weather, settling, or poor installation can crack or separate these pipes. A backed-up main sewer line, usually caused by tree roots or grease buildup, can also force gas into the house.
Cracks in the sewer line itself, especially in older homes with clay or cast-iron pipes, can leak gas into the soil around your foundation and into basements or crawl spaces. If you smell sewer gas only in one room, the problem is usually a local drain or trap. If the smell is throughout the house or concentrated in the basement, the issue is likely the main line or vent stack.
What to do if you smell sewer gas
Open windows when ready to ventilate the space. Do not assume the smell will go away on its own. If the smell is strong or persists after ventilation, leave the house and call a plumber. If you feel dizzy, nauseous, or have difficulty breathing, leave the house and seek fresh air. Do not re-enter until a professional has checked the source.
For a temporary fix, pour water down any drains that have not been used recently — this refills the P-trap and restores the seal. If the smell returns within days, the problem is not a dry trap; it is a leak or vent failure that needs professional repair. Do not delay on this. A sewer gas leak is a sign of a structural problem that will only worsen and may eventually affect your home's foundation or create a health hazard.
Document when the smell occurs — is it constant, or only after heavy rain? Does it come from one drain or the whole house? This information helps a plumber narrow down the source. If you have a septic system rather than a municipal sewer, the same rules explore, but the source is more likely to be a failing tank or a blocked drain field.
Sewer gas and long-term health effects
Chronic low-level exposure — living in a house with a slow sewer leak for months or years — can cause persistent respiratory irritation, worsening asthma, and general malaise. Some people report headaches that improve only after the leak is fixed. There is no evidence that brief or occasional exposure causes permanent damage, but ongoing exposure in a poorly ventilated space can.
If you have lived with sewer gas smell for a long time and have developed new respiratory symptoms, see a doctor and mention the exposure. Sewer gas exposure is not common enough that most doctors will think to ask about it, so you need to bring it up. Once the source is repaired, symptoms usually improve within weeks as your respiratory system recovers.
Frequently Asked Questions
Can sewer gas kill you?
Yes, but only at concentrations far higher than what leaks into homes. Workers who enter sewers or septic tanks without proper ventilation can lose consciousness or die. In a house, you would need a completely sealed basement with a major sewer line break to reach dangerous levels. If you smell sewer gas in your home, the source needs repair, but it is not an when ready life threat.
How long does it take to get sick from sewer gas?
Symptoms like headache and nausea can start within minutes of exposure to moderate concentrations. Brief exposure — a few minutes — usually causes only temporary discomfort. Prolonged exposure over hours or days is what causes lasting respiratory irritation or more serious effects.
Is it safe to sleep in a room that smells like sewer gas?
Not regularly. One night will not cause permanent harm, but sleeping in a room with sewer gas night after night exposes you to chronic low-level inhalation. This can worsen asthma, cause persistent headaches, and irritate your respiratory system. Find and repair the source rather than adapt to the smell.
Will sewer gas go away on its own?
No. Sewer gas smell means there is a leak, a blocked drain, or a vent failure. These problems do not self-repair and usually worsen over time. Pouring water down unused drains can temporarily mask the smell by refilling the P-trap, but if the smell returns, the underlying problem remains and needs professional attention.
What should I do if I feel sick from sewer gas?
Leave the area and get fresh air when ready. Open windows in other parts of the house. If symptoms persist after you have been outside for 30 minutes, or if you have difficulty breathing, seek medical attention. Tell the doctor you were exposed to sewer gas so they can assess your respiratory system properly.