Sewer gas can make you sick, but the risk depends on how much you breathe and for how long
Sewer gas is a mixture of hydrogen sulfide, methane, ammonia, and carbon dioxide that forms in sewage. Breathing small amounts — the occasional whiff from a drain — causes no lasting harm. Breathing larger amounts or breathing it regularly can trigger headaches, nausea, dizziness, and respiratory irritation. In rare cases, very high concentrations can cause loss of consciousness or death, but this almost never happens in homes.
The danger is real but proportional. A single exposure to sewer gas smell from a backed-up toilet or slow drain will not poison you. Chronic low-level exposure in a home with a persistent leak or vent problem can cause ongoing symptoms that feel like a sinus infection or mild flu. The people at highest risk are sewer workers and plumbers who spend hours in confined spaces with active sewage.
Key Takeaways
- Brief exposure to sewer gas smell causes temporary discomfort but no permanent damage to most people.
- Hydrogen sulfide, the main toxic component, irritates the eyes, nose, and throat at low concentrations and can cause more serious symptoms at high levels.
- Chronic exposure in a home — from a leaking vent stack, cracked sewer line, or blocked drain — can produce headaches, fatigue, and nausea that persist until the source is fixed.
- Children, elderly people, and anyone with asthma or respiratory disease are more sensitive to sewer gas and may experience symptoms at lower concentrations.
What happens when you breathe sewer gas
Hydrogen sulfide is the component that causes most of the symptoms. At concentrations below 10 parts per million (ppm), it irritates the eyes, nose, and throat. You notice the smell — a rotten-egg odor — and may feel mild discomfort. At 15 ppm and above, irritation becomes more pronounced. At 100 ppm, exposure for even a few minutes can cause headache, dizziness, and nausea. At 300 ppm or higher, loss of consciousness and death become possible, but reaching these levels in a home is extremely rare.
Methane, another component of sewer gas, is not toxic at the concentrations found in homes. It is odorless and colorless. The danger from methane is explosion risk in confined spaces, not poisoning. Ammonia and carbon dioxide contribute to the irritation but are less acutely dangerous than hydrogen sulfide at typical home exposure levels.
Your body's response is usually protective. The smell triggers you to move away or open a window. Your eyes water, your nose runs, and you feel uncomfortable — all signals to leave the area. This discomfort is the system working as designed.
Symptoms of short-term sewer gas exposure
A single exposure lasting minutes to an hour produces symptoms that fade once you leave the area. These include eye irritation and tearing, nasal irritation and congestion, sore throat, mild headache, nausea, and dizziness. Some people also report a temporary cough or feeling lightheaded. These symptoms usually resolve within an hour of breathing fresh air.
If you experience these symptoms after a brief exposure — such as opening a backed-up toilet or standing over a slow drain — the exposure is not dangerous. Wash your face, drink water, and move to fresh air. The symptoms will pass. You do not need medical attention unless they persist for hours or worsen.
When chronic exposure becomes a problem
Ongoing exposure to low levels of sewer gas in your home is different. This happens when a sewer vent is blocked, a sewer line is cracked, or a drain trap has dried out. Instead of a single whiff, you breathe small amounts throughout the day. Over days or weeks, this can produce persistent headaches, fatigue, difficulty concentrating, and a feeling of general malaise that resembles a lingering cold or sinus infection.
People living in a home with chronic sewer gas exposure often do not connect their symptoms to the source. They may visit a doctor thinking they have a viral infection or allergies. The symptoms improve only when the sewer problem is fixed. If you notice a persistent sewer smell in your home and also have unexplained headaches or fatigue, the two are likely connected.
The longer the exposure, the more likely symptoms become. Someone breathing low-level sewer gas for a few hours may feel nothing. Someone breathing it for weeks will likely develop symptoms. This is why plumbers and sewer workers who spend hours in these environments use respiratory protection.
Who is at higher risk
Children under five have smaller airways and breathe faster than adults, so they inhale more sewer gas per breath. Elderly people often have weaker respiratory systems and may be more sensitive to irritation. Anyone with asthma, chronic bronchitis, or other lung disease will experience symptoms at lower concentrations than a healthy adult.
Pregnant people should avoid sewer gas exposure because the stress and discomfort can affect pregnancy, though sewer gas itself does not cross the placenta or harm the fetus directly. People with heart disease should also be cautious because the stress response to sewer gas exposure can strain the cardiovascular system.
If you live with someone in a high-risk group and notice sewer gas smell in your home, fixing the source becomes more urgent. The same exposure that causes mild discomfort in a healthy adult may cause significant symptoms in a child or elderly person.
How to reduce your exposure at home
The first step is finding the source. A persistent sewer smell usually comes from one of four places: a dried-out drain trap, a blocked or damaged vent stack, a cracked sewer line, or a backed-up sewer system. A dried-out trap is the easiest to fix — pour water down the drain to refill it. A blocked vent stack may need a plumber to clear it. A cracked line or backed-up system requires professional repair.
While waiting for a repair, you can reduce exposure by increasing ventilation. Open windows, run exhaust fans, and avoid spending long periods in the room where the smell is strongest. Do not ignore the smell or assume it will go away on its own. Sewer gas smells bad for a reason — it signals a problem that will not resolve without action.
If you rent, report the sewer smell to your landlord in writing. Most jurisdictions require landlords to maintain plumbing systems in working order. A persistent sewer smell is a maintenance issue, not a cosmetic one.
When to seek medical attention
Seek medical attention if symptoms persist for more than a few hours after leaving the area with sewer gas smell, if you lose consciousness, or if you have difficulty breathing that does not improve with fresh air. Tell your doctor you were exposed to sewer gas so they can rule out other causes.
If you work in sewage or plumbing and experience regular symptoms — headaches, nausea, or respiratory irritation — talk to your employer about respiratory protection. Proper equipment (a respirator rated for hydrogen sulfide) reduces exposure significantly. Do not assume symptoms are normal or unavoidable.
If a child or elderly person in your home has unexplained symptoms and you notice sewer gas smell, have the plumbing inspected. Fixing the source is often faster and cheaper than repeated doctor visits for symptoms that have a clear cause.
Frequently Asked Questions
Can sewer gas cause permanent lung damage?
Brief exposure does not cause permanent damage. Chronic exposure at high levels can, but this is rare in homes. Sewer workers who use respiratory protection do not develop lung damage. If you have ongoing sewer gas exposure in your home, fixing it before symptoms become severe prevents any lasting effects.
Is sewer gas flammable?
Methane in sewer gas is flammable, but only in confined spaces where it can accumulate to explosive concentrations. In a home with normal ventilation, methane disperses too quickly to ignite. The risk is in sewers, septic tanks, and other enclosed systems, not in living spaces.
Can you die from sewer gas in your home?
Death from sewer gas in a home is extremely rare. It requires very high concentrations over a sustained period, which almost never happens in residential plumbing. Sewer workers in confined spaces face real risk, which is why they use respiratory protection. A homeowner smelling sewer gas is not in when ready danger.
Does sewer gas smell mean the gas itself is dangerous?
The smell is a warning signal, not a measure of danger. You can smell hydrogen sulfide at very low concentrations — as low as 0.5 ppm — long before it causes harm. A strong smell means the source is close or the concentration is higher, but it does not mean you are being poisoned. Move away and fix the source.
What if I have been smelling sewer gas for weeks?
Weeks of exposure is long enough to cause persistent symptoms like headaches and fatigue. Call a plumber to locate and fix the source. Do not wait for symptoms to worsen. Once the source is fixed, symptoms usually improve within days as your body recovers from the irritation.