Yes, sewer gas can make you sick, but only at high concentrations or with prolonged exposure
Sewer gas is a mixture of gases produced by decomposing waste in your septic system or municipal sewer line. The main components are methane, hydrogen sulfide (which smells like rotten eggs), ammonia, and carbon dioxide. In small amounts—the trace levels that occasionally seep into a home—sewer gas causes temporary discomfort: headaches, nausea, or eye irritation. At higher concentrations, it can trigger more serious symptoms, and in rare cases, it poses real danger.
The risk depends on how much gas enters your home and how long you breathe it. A single whiff from a backed-up drain is not a medical emergency. A persistent leak that fills a basement or crawl space over weeks is a different problem. Most homeowners encounter sewer gas as a smell problem first, which is actually your warning system working—it tells you something is wrong with your plumbing before the gas reaches dangerous levels.
Key Takeaways
- Sewer gas at low levels causes temporary headaches, nausea, and eye irritation; high concentrations can cause dizziness, loss of consciousness, and in extreme cases, death.
- Hydrogen sulfide, the rotten-egg-smelling component, is the most toxic part of sewer gas and is also the easiest to detect by smell.
- A persistent sewer smell in your home signals a broken vent pipe, cracked sewer line, or failed trap seal—all fixable plumbing problems.
- Ventilation and identifying the source are your first steps; call a plumber if the smell does not clear within a few hours or returns regularly.
- People with respiratory conditions, the elderly, and young children are more vulnerable to sewer gas symptoms.
What sewer gas does to your body at different exposure levels
At the concentrations most homeowners encounter—a few minutes of smell from a backed-up drain or a slow leak—sewer gas causes what you might call discomfort symptoms. These include headache, nausea, dizziness, and irritation of the eyes, nose, and throat. These symptoms usually fade within minutes to an hour once you leave the area or the source is ventilated.
Moderate exposure over hours—for example, spending a full day in a basement with a slow sewer leak—can produce more persistent symptoms: fatigue, difficulty concentrating, and worsening nausea. Some people report a temporary loss of appetite or mild respiratory irritation that feels like a chest cold.
High concentrations of sewer gas, which are rare in homes but can occur in confined spaces like sewers or septic tanks, cause loss of consciousness, seizures, and in extreme cases, death. Hydrogen sulfide is the culprit here; it can paralyze the olfactory nerve (the nerve that lets you smell), so at very high levels you stop smelling it even as it damages your lungs and nervous system. This is why sewer workers and septic tank cleaners use respirators and never enter tanks alone.
Who is most at risk from sewer gas exposure
People with asthma, chronic obstructive pulmonary disease (COPD), or other respiratory conditions are more sensitive to sewer gas. Even low concentrations can trigger coughing, wheezing, or shortness of breath in these individuals. If you have a respiratory condition and notice these symptoms coinciding with a sewer smell, treat it as urgent and ventilate when ready.
Infants and young children are also more vulnerable because their lungs are still developing and their bodies are smaller, so the same concentration of gas has a larger effect. Elderly people and anyone with a weakened immune system may experience symptoms more severely or recover more slowly.
If you live alone or with only one other person, a sewer gas leak is less likely to be caught early because fewer people are around to notice the smell. If you have mobility issues or spend most of your time in one room, you may not be able to leave the affected area quickly if exposure becomes uncomfortable.
Common sources of sewer gas in homes
Dry or failed P-traps are the most common culprit. The P-trap is the U-shaped bend under your sink, toilet, or shower drain. It holds standing water that acts as a seal, blocking sewer gas from rising back up through the pipe. If a drain sits unused for weeks, the water evaporates and the seal breaks. If the trap is cracked or installed incorrectly, gas leaks past it.
Broken or blocked vent pipes are the second major source. Your plumbing system has vent pipes that run up through your roof. They allow sewer gas to escape safely outside and let air into the system so drains flow properly. If a vent pipe is cracked, clogged with leaves or bird nests, or damaged by weather, gas backs up into the home instead of venting outside.
Cracked sewer lines or septic tank leaks can allow gas to seep into the soil around your foundation and then into your basement or crawl space. This usually produces a persistent smell that does not go away with ventilation. Backed-up sewers during heavy rain or when the municipal line is blocked can force gas and waste back into your home through drains and toilets.
Loose toilet seals or cracks in the toilet base allow gas to escape into the bathroom. A toilet that rocks slightly when you sit on it or that smells even after flushing may have a failed wax ring—the seal between the toilet and the drain pipe.
Steps to take if you smell sewer gas in your home
First, open windows and doors to ventilate the space. Sewer gas is not explosive at the concentrations found in homes, but fresh air will dilute it and clear your symptoms quickly. If the smell is strong or you feel dizzy, nauseous, or short of breath, leave the house and call a plumber from outside.
Next, try to locate the source. Is the smell strongest near a particular drain, toilet, or in the basement? Does it come and go, or is it constant? A smell that appears only after heavy rain suggests a backed-up sewer or a crack in the line. A smell from under the sink suggests a dry trap or a leaking connection. A smell from the toilet suggests a failed wax ring or a vent pipe problem.
If the source is a dry trap—you have a drain you have not used in weeks—run water down it for 30 seconds. This refills the trap and restores the seal. If the smell clears within an hour, the problem is solved.
If the smell persists, returns regularly, or you cannot find the source, call a licensed plumber. Do not attempt to open or inspect septic tanks or sewer lines yourself. A plumber can use a camera to inspect the line, test for cracks, and identify vent pipe problems. They can also perform a smoke test, which involves introducing non-toxic smoke into the system to reveal leaks.
When to seek medical attention
If you experience chest pain, severe shortness of breath, loss of consciousness, or seizures in connection with sewer gas exposure, call emergency services when ready. These are rare but serious symptoms that require when ready care.
If you have a respiratory condition and sewer gas triggers an asthma attack or COPD flare-up, use your rescue inhaler and leave the area. If symptoms do not improve within 15 minutes, seek medical attention. Bring information about the sewer gas exposure with you so the doctor understands the context.
If you or a family member experience persistent headaches, fatigue, or respiratory irritation that coincides with a sewer smell in your home, see your doctor and mention the sewer gas exposure. These symptoms usually resolve once the source is fixed, but your doctor can rule out other causes and monitor your recovery.
How to prevent sewer gas problems
Use all your drains regularly. Run water down the kitchen sink, bathroom sinks, and shower at least once a week. If you have a guest bathroom or basement drain that sits unused, pour a cup of water down it monthly to keep the trap seal intact.
Have your plumbing vent pipes inspected during your annual home maintenance check. A plumber can confirm they are clear of debris and properly sealed where they exit the roof. If you notice a vent pipe that is cracked, rusted, or has a loose cap, have it repaired promptly.
If you have a septic system, have it pumped every three to five years (the exact interval depends on tank size and household size). A full tank can back up and allow gas to escape into the home. Keep records of your pumping schedule.
After heavy rain, check your basement or crawl space for standing water or new smells. If you notice either, it may signal a backed-up sewer or a crack in the line. Call a plumber to inspect before the problem worsens.
Frequently Asked Questions
Can sewer gas cause permanent damage to my lungs?
Occasional exposure to low concentrations of sewer gas does not cause permanent lung damage. However, prolonged exposure to high concentrations—which is rare in homes but can occur in septic tanks or sewers—can cause lasting injury to lung tissue and the nervous system. If you work in an industry with regular sewer exposure, use proper respiratory protection.
Why does sewer gas smell like rotten eggs?
Hydrogen sulfide, one of the main components of sewer gas, naturally smells like rotten eggs. This smell is actually protective—it alerts you to a problem before the gas reaches dangerous concentrations. If you stop smelling it despite the source still being present, that is a sign of very high exposure and you should leave when ready.
Is sewer gas flammable or explosive?
Methane, a component of sewer gas, is flammable in high concentrations, but the levels found in homes are too low to ignite. Sewer gas is not a fire or explosion hazard in typical residential plumbing situations.
Can I fix a sewer gas smell myself, or do I need a plumber?
If the smell comes from a dry trap under a sink or shower, you can refill it yourself by running water down the drain. For any other source—a backed-up sewer, a cracked line, a failed toilet seal, or a vent pipe problem—call a plumber. These require tools and informed to diagnose and repair safely.
How long does it take to get sick from sewer gas?
Symptoms from low-level exposure appear within minutes—usually a headache or nausea. High-concentration exposure can cause loss of consciousness within seconds. The speed depends on the concentration and your individual sensitivity. If you feel symptoms, leave the area when ready and ventilate.