Sewer gas poisoning is a health emergency that should never be put on hold. It’s especially dangerous because you can be exposed to sewer gas without realizing it, and its early symptoms are easy to mistake for a cold, stress, or a bad night’s sleep.
So, how do you treat sewer gas poisoning? The first and most important step is to get the affected person into fresh air right away and call for emergency help if symptoms are severe. There is no specific antidote for hydrogen sulfide, the main toxic gas in sewer gas, so treatment focuses on supportive care: restoring normal breathing, stabilizing vital functions, and removing the person from further exposure.
In this guide, we’ll explain what sewer gas is, what causes leaks inside the home, how to recognize the signs of poisoning, how it’s treated, and how to fix the source so it doesn’t happen again.
Key Takeaways
If you only have a minute, here’s what you need to know about sewer gas poisoning:
Fresh air comes first. Get everyone out of the affected area and into fresh air immediately.
Call 911 for severe symptoms, such as trouble breathing, confusion, or lost consciousness. For milder symptoms, call Poison Control at 1-800-222-1222.
There is no antidote for hydrogen sulfide poisoning. Hospitals treat it with oxygen, breathing support, and continuous monitoring.
Don’t trust your nose. Do not rely on odor to determine the safety of an area after exposure. High concentrations of hydrogen sulfide can deaden your sense of smell, so the rotten egg odor can fade even as the danger grows.
Most household leaks come from simple plumbing problems, like dry drain traps, blocked vents, or loose toilets, and a plumber can usually fix them quickly.
What Is Sewer Gas?
Sewer gas is a complex mixture of toxic and nontoxic gases produced when organic material, such as human waste, food scraps, and other household waste, breaks down in sewer and septic systems. As bacteria digest this waste without oxygen, they release gases that collect inside pipes, septic tanks, and municipal sewer lines.
In a properly working plumbing system, these gases never enter your living space. Water-filled drain traps block them at every fixture, and vent pipes carry them safely out through your roof as gases are also emitted when organic material breaks down.
When part of that system fails, sewer gas can seep into your home. In small amounts, it’s mostly an unpleasant nuisance. In high concentrations, especially in enclosed spaces like basements and small bathrooms, it can be extremely dangerous and even deadly, even though Hydrogen Sulfide is also produced naturally in small amounts in humans and animals.
Hydrogen Sulfide, Methane, and Other Gases in Sewer Gas
Hydrogen sulfide and methane are the primary components of sewer gas. Hydrogen sulfide gives sewer gas its rotten egg smell and is the most toxic part of the mix. It’s also heavier than air, so it tends to collect in low areas like basements, crawl spaces, and floor drains.
Methane is odorless and highly flammable. On its own, it isn’t very toxic, but it can build up to explosive levels and displace oxygen in a room.
Sewer gas can also contain ammonia, which irritates the eyes, nose, and throat, and carbon dioxide, which can reduce the oxygen available to breathe. It may also include small amounts of nitrogen dioxide, which can cause respiratory issues. Together, these gases carry a range of health effects, from mild irritation to life-threatening poisoning.
What Causes Sewer Gas Leaks Inside the Home?
Even a well-designed plumbing system can develop problems over time. It may take just one small crack or loose connection in a drain pipe to let sewer gas into your home.
Common causes of indoor sewer gas leaks include:
Loose or damaged plumbing vents
Corroded or rusted septic and drain pipes
Cracked, broken, or damaged sewer pipes
Air vents blocked by dirt, debris, or other buildup
Bird nests or other blockages in roof vents
Drain pipes clogged with hair, toilet paper, or other waste
Dry drain traps in sinks, tubs, or floor drains that aren’t used often
Toilets with a worn wax ring or a loose seal to the sewer pipe
Leaks can also occur even when you can’t smell anything, which makes hidden gas problems especially dangerous, and identifying the source can be difficult when odors are intermittent or trapped inside walls or floors.
In dry climates like Reno and Las Vegas, water in drain traps evaporates faster, so dry traps are one of the most common causes we see in local residential plumbing systems.
Sewer Gas vs. Natural Gas vs. Carbon Monoxide
Sewer gas isn’t the only gas hazard in a home. Natural gas and carbon monoxide can also build up indoors, and some of their symptoms overlap with sewer gas exposure.
It’s important to know how they differ, because each one requires a different response. A sewer gas leak is usually a plumbing problem.
A natural gas leak is a fire and explosion hazard that your gas company needs to handle. Carbon monoxide comes from fuel-burning appliances and is the most common cause of fatal gas poisoning in homes.
The table below gives a quick comparison, and the sections that follow explain each gas in more detail.
| Gas | Smell | Common source | What to do |
|---|---|---|---|
| Sewer gas | Rotten eggs | Drains, toilets, basement | Ventilate, leave, call a plumber |
| Natural gas | Rotten eggs (added odorant) | Stove, furnace, water heater, gas meter | Leave, call the gas company or 911 from outside |
| Carbon monoxide | None | Furnaces, water heaters, stoves, cars | Leave, call 911 |
Natural Gas Leaks
Up to half of U.S. households use natural gas for energy, mainly for heating, water heaters, and stoves. Natural gas is mostly methane, which is colorless and odorless in its natural state.
Leak estimates suggest natural gas leaks release 21.2 kilotons of methane annually. Utility companies add chemicals called mercaptans to give it a sulfur smell so leaks are easier to detect.
Natural gas leaks can occur even without a detectable smell, especially very small ones. Research on gas stoves estimates that about three-quarters of their methane emissions happen while the stoves are turned off, from small leaks in fittings and connections.
Some volatile organic compounds (VOCs) found in natural gas have also been linked to health effects, including possible disruption of hormonal functions.
If you smell gas near your stove, furnace, or water heater, treat it as a natural gas leak. Leave the home without using any switches, and call your gas company or 911 from outside.
Carbon Monoxide and Carbon Monoxide Poisoning
Carbon monoxide (CO) is a colorless, odorless gas produced by incomplete combustion of fuels such as natural gas, oil, wood, and gasoline. It is not a normal part of sewer gas, but it’s the leading cause of fatal gas poisoning in homes. According to the CDC, more than 400 Americans die from unintentional carbon monoxide poisoning each year.
Carbon monoxide poisoning causes symptoms similar to sewer gas exposure, including headaches, dizziness, nausea, and fatigue. CO binds to the hemoglobin in your blood far more strongly than oxygen does, which reduces your blood’s ability to carry oxygen to your brain and other organs.
The key difference is that sewer gas usually smells like rotten eggs, while carbon monoxide gives no warning at all. The only reliable way to detect it is with a carbon monoxide detector. If a CO alarm goes off, leave the home immediately and call 911.
Signs and Symptoms of Sewer Gas Poisoning
Recognizing the signs of sewer gas exposure early can prevent serious harm. The symptoms depend mainly on how much gas is in the air and how long you’ve been breathing it.
At low levels, symptoms tend to build slowly and are easy to blame on something else, like allergies, a cold, or poor sleep. At high levels, symptoms can appear within minutes and quickly become life-threatening.
One useful clue is timing. If you or your family feel worse at home and better after spending time somewhere else – an example being symptoms easing after leaving for work or school – an indoor gas problem may be the cause. Pay extra attention if several people in the household, other persons in the home, or even pets show similar symptoms at the same time.
The Rotten Egg Smell
The first warning sign is usually a rotten egg smell coming from a drain, toilet, or basement. People can recognize this odor at very small amounts of hydrogen sulfide, at a detection threshold of 10 parts per billion (ppb) or lower. That makes your nose a sensitive early warning system at low levels.
However, this warning can fade at higher concentrations. Around 100 ppm and above, hydrogen sulfide can paralyze your sense of smell, so the odor may disappear even though the gas is still present. People also get used to a constant smell over time and stop noticing it.
If a sewer smell suddenly goes away without a clear reason, don’t assume the problem is fixed. Ventilate the area and have the source checked.
Symptoms of Low-Level Exposure
Symptoms of low-level sewer gas exposure often include:
Fatigue for no clear reason
Headaches
Nausea or vomiting
Dizziness
Trouble concentrating
Poor memory
Eye irritation
Coughing, sore throat, and other respiratory issues
People with asthma or other breathing problems may notice symptoms sooner and more severely. Children, older adults, and pregnant women may also be more sensitive.
Low-level symptoms usually improve once the person gets into fresh air, but they often return after someone goes back to the workplace or home if the leak remains unfixed.
Symptoms of High-Level Exposure
High concentrations of sewer gas can quickly become life-threatening. Severe exposure can cause extreme dizziness, confusion, and difficulty breathing. It can also cause fluid in the lungs (pulmonary edema), seizures, lost consciousness, and death.
Hydrogen sulfide can cause immediate loss of consciousness at 250 ppm, making rapid evacuation critical.
High-level exposure is rare in homes, but it can happen when gas builds up in a small, poorly ventilated space.
Examples include a basement with a broken sewer line, a pit near a septic tank, or a room where a floor drain has dried out, though this type of buildup is more common in wastewater or confined-space industry settings than in a typical house.
If someone collapses or becomes confused in an area that smells like sewage, treat it as an emergency. Call 911 right away, and don’t enter the space yourself without protection. Rescuers can be overcome by the same gas.
Health Risks of Sewer Gas Exposure
The toxicity of sewer gas depends on its concentration, how long the exposure lasts, and the person’s overall health. A brief whiff from a floor drain is very different from hours spent breathing gas in a closed room.
Sewer gas carries three main risks: poisoning from hydrogen sulfide, fire or explosion from flammable gases like methane, and suffocation when other gases push oxygen out of the air. Each risk becomes more serious in enclosed spaces, where gas can build up with nowhere to go.
Understanding these risks helps you respond correctly. A strong sewer smell doesn’t just mean an unpleasant home. It can be a sign of a real safety hazard.
Hydrogen Sulfide Poisoning
Hydrogen sulfide is the biggest danger in sewer gas because its effects can become severe very quickly. It is the second-most common cause of fatal gas inhalation after carbon monoxide, and it accounts for about 7.7% of occupational gas-related deaths in the U.S.
Hydrogen sulfide interferes with how your cells use oxygen, which particularly affects the brain, heart, and nervous system. Low levels cause eye irritation, coughing, and breathing problems.
At around 250–300 ppm, prolonged exposure can cause serious lung damage and death within hours. At 500–700 ppm, people can collapse within minutes. Around 1,000 ppm can cause respiratory paralysis, loss of consciousness, and death almost immediately.
Chronic exposure to lower levels of gas byproducts can also cause lasting neurological symptoms, such as memory problems and fatigue.
Some human studies have examined long-term neurological effects, but the evidence is mixed, and the possibility of subtle harm may be missed when exposure levels are hard to measure precisely.
Oxygen therapy is a standard treatment for hydrogen sulfide inhalation and is commonly used in hospitals to support breathing and recovery.
Explosion and Fire Risk
Methane and hydrogen sulfide are both highly flammable. Methane can ignite when it makes up about 5% to 15% of the air in a space. If sewer gas builds up in an enclosed area, a spark from an appliance, light switch, or open flame could ignite it.
Pouring gasoline, oil, paint thinner, or other flammable liquids down the drain increases this risk, because their vapors can collect in your plumbing system. Dispose of these liquids at a household hazardous waste facility instead.
This fire risk is why you should never light a match, use a lighter, or flip a switch when you notice a strong gas smell. Leave the area first, then call for help from a safe location.
Suffocation in Enclosed Spaces
In enclosed spaces like basements, crawl spaces, and sewer pits, methane, carbon dioxide, and other gases can displace the oxygen in the air. Because hydrogen sulfide and carbon dioxide are heavier than air, they tend to sink and collect in low areas.
Low oxygen levels can cause severe headaches, rapid breathing, dizziness, poor judgment, and unconsciousness. At high gas concentrations, the lack of oxygen can cause sudden death, sometimes with little warning.
This is why confined spaces like septic tanks and sewer pits should only be entered by trained professionals, since the nature of the space determines what testing, ventilation, and breathing protection are needed. Homeowners should never climb into a septic tank or sewer access point, even briefly.
How to Treat Sewer Gas Poisoning: Immediate Steps
If you or someone in your home shows signs of sewer gas poisoning, act quickly. The faster a person is removed from the gas, the better their chance of a full recovery.
Treatment starts at home with four steps: get to fresh air, call for help, give basic first aid until help arrives, and rinse the gas off skin and eyes. Most people with mild exposure feel better soon after reaching fresh air. More serious cases need emergency medical care.
Throughout these steps, keep your own safety in mind. You can’t help anyone if you’re overcome by the gas too.
1. Leave the Affected Area and Get Fresh Air
Your first priority is safety. Get everyone, including pets, out of the affected area and into fresh air as soon as possible. If it’s safe to do so on your way out, open windows and doors to ventilate the space.
Don’t light matches, use lighters, or turn electrical switches or appliances on or off. Any spark could ignite flammable gas. Leave lights and appliances exactly as they are, and don’t start a car parked in an attached garage.
Once outside, move a safe distance away from the house. Don’t go back inside until the source has been found and the air has been cleared, even to grab belongings. A plumber or emergency responder can tell you when it’s safe to return.
2. Call for Help
Call 911 immediately if anyone has trouble breathing, chest pain, confusion, seizures, or has lost consciousness. Tell the dispatcher you suspect gas exposure so responders can bring the right equipment.
For mild symptoms, like a headache or nausea that improves in fresh air, call Poison Control at 1-800-222-1222. The service is free, open 24/7, and staffed by experts who can tell you whether you need to see a doctor.
Once everyone is safe, call a licensed plumber to find and fix the source of the leak. If you suspect natural gas instead of sewer gas, call your gas company. Most gas companies will send someone out to check for leaks free of charge.
3. Provide First Aid Until Help Arrives
Keep the affected person in fresh air, sitting up if they’re conscious and breathing, and stay with them. Loosen tight clothing around the neck and chest so they can breathe more easily. If they’re unconscious but breathing, place them on their side in the recovery position.
If the person isn’t breathing, start CPR if you’re trained, and follow the 911 dispatcher’s instructions. Never enter an area with a strong gas buildup to rescue someone without proper protective equipment. Many sewer gas deaths involve would-be rescuers.
If the person fell or may have a head or neck injury, avoid moving their head and neck unless you must move them to get them away from the gas. Keep them warm and calm until paramedics arrive.
4. Decontaminate Skin and Eyes
Remove any clothing that smells strongly of gas and seal it in a double plastic bag. Rinse irritated skin with plenty of water, and flush irritated eyes with clean water for at least 15 minutes. Remove contact lenses first if possible.
In rare cases, mostly in industrial settings, skin can come into contact with compressed or liquefied gas and suffer frostbite. Medical guidelines recommend rewarming the affected area in a warm water bath at 102–108°F (39–42°C) for about 30–40 minutes, ideally under medical supervision. Don’t rub frostbitten skin, which can cause more damage.
After these first steps, anyone with ongoing symptoms should get medical care to check for respiratory or heart problems.
Medical Treatment for Sewer Gas Poisoning
There is no specific antidote for hydrogen sulfide poisoning, so supportive care is the primary treatment. In the absence of a single test that confirms sewer gas poisoning in every case, doctors rely on the clinical picture and exposure history. Professional medical treatment focuses on stabilizing vital functions.
At the hospital, treatment may include oxygen therapy, breathing support with a ventilator in severe cases, and medications to control symptoms like seizures or fluid in the lungs. Continuous monitoring of heart rate and blood pressure is standard in severe cases.
Doctors may also run tests to check the lungs, heart, and brain for damage, and they judge severity based on exposure history and the presence of respiratory or neurological findings.
They may use clinical test results and exposure information collected during evaluation to assess oxygen problems and organ stress.
In rare, severe cases, doctors may consider other treatments, such as hyperbaric oxygen, although published analysis of severe Hydrogen Sulfide cases is limited, so the evidence for them remains uncertain.
Treatment and recovery depend on several factors:
The person’s overall health and age
Pre-existing conditions such as asthma or heart disease
Smoking or drinking habits
Past exposure to toxic chemicals or certain medications
The concentration of the gas and how long the person was exposed
Most people with mild exposure recover fully once they’re in fresh air. After severe exposure, follow up with your doctor about any lasting respiratory, heart, or neurological symptoms.
How to Fix the Source of a Sewer Gas Leak
Once everyone is safe, the next step is finding and fixing the source of the leak. Treating the symptoms without fixing the leak means the problem will come back, often the next time you’re home for a few hours.
Some causes, like dry drain traps, are simple for homeowners to fix in a few minutes. Others, like cracked sewer lines, blocked roof vents, and damaged toilet seals, need a professional plumber with the right tools and safety equipment.
If you’re not sure where the smell is coming from, start by checking drains you rarely use. If the smell continues, call a plumber for a full inspection.
Refill Dry Drain Traps
Every drain has a U-shaped trap that holds water, and that water seal blocks sewer gas from coming up through the drain. If a sink, shower, or floor drain goes unused for a while, the water can evaporate and let sewer gas into your home.
The fix is easy: run water down each drain for about a minute to refill the trap. For drains you rarely use, repeat this every few weeks. Guest bathrooms, basement floor drains, and laundry room drains are common culprits.
In dry Nevada air, traps can dry out faster than in humid climates. For vacation homes or drains you almost never use, a plumber can install a trap primer, a device that keeps the trap filled automatically.
Inspect and Clear Roof Vents
Plumbing vents on your roof let sewer gas escape safely outside. They also balance the air pressure in your pipes so water drains smoothly and traps stay full.
When debris, leaves, or bird nests block these vents, gas can be pushed back into your home instead. A blocked vent can also pull water out of your drain traps as other fixtures drain, which lets even more gas in. Signs of a blocked vent include gurgling drains, slow drainage, and a sewer smell that comes and goes.
Clearing roof vents involves working on the roof and inside the vent pipe, so it’s safest to let a plumber inspect and clean them. A plumber can also add a vent cap or screen to keep debris out.
Reseal Loose Toilets
The seal between a toilet and the sewer pipe can wear out over time, especially if the mounting bolts are loose or the wax ring is damaged. When that seal breaks, sewer gas can escape from around the toilet’s base.
A toilet that rocks, leaks at the base, or smells like sewer gas usually needs a new wax ring. Water stains or soft flooring around the toilet are other warning signs, because leaking water can damage the subfloor.
A plumber can check the mounting bolts, wax ring, and flange for damage or hidden cracks, then reseal or replace the toilet as needed. This is usually a quick, affordable repair when it’s caught early.
Find Cracked or Damaged Sewer Lines
Leaks in sewer pipes or vents are often the main cause of unnoticed sewer gas exposure. Pipes can crack from age, corrosion, shifting soil, or tree roots, and the damage is usually hidden inside walls, under floors, or underground.
To find hidden leaks, a plumber may use a sewer camera inspection to see inside the pipes and collect visual data that confirms where gas is escaping and where hidden damage is discovered.
They may also perform smoke testing, which pushes harmless smoke through the plumbing system so it escapes wherever there’s a crack, or dye testing to trace leaks; these methods help refer the repair to the exact damaged section instead of guessing.
Once the leak is found, the plumber can repair or replace the damaged section of the sewer line. If buildup is causing the problem, hydro-jetting can clear the line with high-pressure water.
How to Prevent Sewer Gas Poisoning
The best way to protect your family is to stop sewer gas leaks before they start. Most prevention steps are simple and inexpensive:
Keep drain traps full by running water in unused drains regularly.
Don’t pour grease, oil, or flammable liquids down your drains.
Install carbon monoxide detectors on every level of your home and near bedrooms. For areas near floor drains or sewer access, consider a detector that also senses hydrogen sulfide.
Keep good ventilation in basements, laundry rooms, and bathrooms.
Watch for warning signs like gurgling drains, slow drainage, or a sewer smell that comes and goes.
Schedule a professional plumbing inspection at least once a year to catch cracked pipes, loose seals, and blocked vents early.
A small repair today is far cheaper, and far safer, than dealing with a serious leak later.
Final Thoughts: How to Treat Sewer Gas Poisoning and Stay Safe
Sewer gas leaks in homes are fairly common, and most are caused by simple plumbing problems a professional plumber can fix quickly. The danger comes when leaks go unnoticed and toxic gases like hydrogen sulfide keep building up.
If you suspect sewer gas poisoning, get to fresh air immediately, call for help if symptoms are severe, and don’t return until the source is fixed. Carbon monoxide poisoning is a separate danger to watch for, because it has no smell at all. Working CO detectors are essential in every home.
To keep your home safe, schedule regular plumbing maintenance and inspections so hidden sewer gas leaks don’t go unnoticed. This article is for general safety information and does not replace emergency medical care or a professional inspection.
If you notice a sewer smell or any of the warning signs above, contact Hawthorne Plumbing, Heating & Cooling for fast, professional help in Reno and Las Vegas.
Frequently Asked Questions
Yes. Even low levels of sewer gas can cause headaches, nausea, dizziness, fatigue, and eye or throat irritation. These symptoms mainly come from hydrogen sulfide and ammonia, which irritate the eyes and airways and interfere with how your body uses oxygen.
High levels can cause breathing problems, fluid in the lungs, loss of consciousness, and death. The risk depends on the gas concentration, how long you’re exposed, and your health. People with asthma, heart disease, or other breathing conditions tend to get sick faster.
If you notice symptoms that improve when you leave home, have your plumbing checked.
Mild symptoms, like headaches and nausea, usually improve within a few hours after you get into fresh air. Most people with low-level exposure make a full recovery with no lasting effects.
Severe exposure is different. It can cause lung, heart, or nervous system damage that takes days, weeks, or longer to heal, and some people have lasting problems with memory, concentration, or breathing. That’s why medical follow-up is important after any serious exposure.
If symptoms like coughing, shortness of breath, or confusion continue after you leave the affected area, see a doctor right away.
No. If you notice a sewer gas smell, ventilate the home and find the source before sleeping there, especially if anyone has symptoms. While you sleep, you can’t notice a worsening smell or early symptoms, and gas can build up in closed bedrooms overnight.
If the smell is faint and no one feels unwell, try refilling unused drain traps and opening windows. If the smell goes away, the problem was probably a dry trap. If the smell is strong, keeps coming back, or anyone feels sick, leave the home and call a plumber or emergency services.
Both can smell like rotten eggs, so they’re easy to confuse. The location of the smell is usually the best clue. Sewer gas typically comes from drains, toilets, floor drains, or the basement. Natural gas usually comes from near gas appliances, like the stove, furnace, or water heater, or from near the gas meter.
A natural gas leak is a fire and explosion risk that needs immediate attention. If you’re unsure which one you smell, treat it as natural gas: leave the home without using switches and call your gas company from outside. They can test for natural gas at no cost.
