Sewer gas can cause real harm, especially with repeated exposure or in high concentrations

Yes, sewer gas is harmful to breathe. The mixture contains hydrogen sulfide, methane, ammonia, and other gases produced by decomposing waste. Hydrogen sulfide is the main concern—it smells like rotten eggs and can damage your respiratory system, eyes, and nervous system even at low levels. A single brief exposure to a bad smell from a drain usually causes only temporary discomfort, but prolonged or repeated exposure carries real health risks.

The danger depends on how much gas you breathe and for how long. A few seconds of odor from a backed-up drain is unlikely to cause lasting harm. Hours spent in a space with active sewer gas leaks—such as a basement with a cracked pipe or a bathroom with a broken vent—can cause headaches, dizziness, nausea, and respiratory irritation that may last days. In extreme cases, high concentrations can cause loss of consciousness or death, though this is rare in homes and usually happens in confined spaces like sewers or septic tanks.

Key Takeaways

  • Hydrogen sulfide in sewer gas irritates your lungs, eyes, and throat; repeated exposure can cause chronic respiratory problems.
  • A brief whiff from a drain is usually harmless, but hours of exposure in a poorly ventilated space can cause headaches, nausea, and dizziness that persist after you leave.
  • Children, elderly people, and anyone with asthma or lung disease face higher risk from sewer gas exposure.
  • The smell itself is a warning sign—if you notice rotten-egg odor in your home, the source needs to be found and sealed to prevent ongoing exposure.

How sewer gas enters your home and lungs

Sewer gas enters your home through breaks in pipes, dry P-traps (the U-shaped bends under sinks and toilets that normally hold water as a seal), or blocked vent pipes on your roof. Once inside, you breathe it in through your nose and mouth, and it travels directly to your lungs. The gases dissolve into the moisture lining your airways and can irritate the tissue there.

The longer the gas stays in contact with your lungs, the more damage it can do. Hydrogen sulfide is particularly reactive—it binds to proteins in your cells and interferes with how they use oxygen. This is why people who work in sewers or septic tank cleaning wear respirators: even trained workers in those jobs face serious risk without protection.

Short-term symptoms from sewer gas exposure

If you breathe sewer gas for a few minutes to an hour, you may notice eye irritation, a scratchy throat, or a mild headache. These symptoms usually fade within an hour of leaving the space and breathing fresh air. Nausea and dizziness can also occur and may last longer—sometimes several hours—even after you step outside.

Some people are more sensitive than others. If you have asthma, emphysema, or another chronic lung condition, even brief exposure can trigger coughing, wheezing, or shortness of breath. Children and older adults also tend to react more strongly. If symptoms do not improve within a few hours of leaving the area, or if you develop chest pain or difficulty breathing, seek medical attention.

Long-term health effects of repeated exposure

People who live in homes with ongoing sewer gas leaks—such as a cracked foundation pipe or a vent that stays blocked—may experience chronic symptoms. Repeated exposure to hydrogen sulfide can cause persistent cough, bronchitis-like symptoms, and increased sensitivity to respiratory infections. Some research suggests long-term exposure may contribute to asthma development in children, though the evidence is still being studied.

Workers in sewage treatment, septic tank maintenance, and related fields face the highest risk. Studies of these workers show higher rates of respiratory disease and neurological symptoms compared to the general population. This is why occupational safety standards require ventilation and respiratory protection in those settings.

Why the smell matters: it is your body's warning system

The rotten-egg smell of sewer gas is not just unpleasant—it is your body's alert that harmful gas is present. Hydrogen sulfide has a very low odor threshold, meaning you can smell it at concentrations far below what causes physical harm. This is actually protective: you notice the problem before damage occurs.

However, if you are exposed to very high concentrations of hydrogen sulfide very quickly, your sense of smell can become "fatigued" or paralyzed. This means you stop smelling the gas even though it is still there and still harming you. This is one reason why sewer workers must use equipment that measures gas levels rather than relying on their nose.

Who is at higher risk from sewer gas

Certain groups face greater danger from sewer gas exposure. Children have smaller lung capacity and breathe faster, so they inhale more gas per breath. Older adults often have reduced lung function and slower recovery. People with asthma, COPD, emphysema, or other chronic lung disease can experience severe reactions to even low levels of hydrogen sulfide.

Pregnant people should also be cautious, as some research suggests hydrogen sulfide may affect fetal development, though evidence is limited. If you fall into any of these groups and suspect sewer gas in your home, have the source identified and repaired rather than waiting to see if symptoms develop.

What to do if you suspect sewer gas in your home

If you notice a persistent rotten-egg smell, do not ignore it. Start by checking the obvious sources: run water in rarely used sinks and toilets to refill dry P-traps, make sure all drains have strainers, and look for visible cracks in basement pipes. If the smell continues, call a plumber to inspect your vent stack (the pipe that runs through your roof) and check for blockages or damage.

While waiting for a plumber, increase ventilation by opening windows and running exhaust fans. Do not spend hours in the affected space, especially if you have respiratory conditions. If the smell is strong enough to cause headaches or dizziness, leave the area and get fresh air when ready. Once the source is sealed, the gas exposure stops and your symptoms should resolve.

Frequently Asked Questions

Can a single breath of sewer gas cause permanent damage?

No. A single breath or even a few minutes of exposure to sewer gas at typical household levels will not cause permanent harm. Your lungs are designed to handle brief irritation. Permanent damage requires either very high concentrations (which are rare in homes) or repeated exposure over weeks or months.

Is sewer gas the same as natural gas?

No. Natural gas is odorless and colorless; utility companies add a chemical smell to it so leaks are detected. Sewer gas is a mixture of decomposition byproducts and smells like rotten eggs. They require different safety responses—a natural gas smell means leave the building and call your gas company when ready, while sewer gas means find and seal the source.

What should I do if I feel dizzy or sick after smelling sewer gas?

Leave the area and breathe fresh air outside for at least 15 minutes. Symptoms usually fade once you are in clean air. If dizziness, nausea, or difficulty breathing continues for more than a few hours, or if you develop chest pain, contact a doctor or poison control. Have a plumber inspect your home to find the source while you recover.

Can sewer gas cause carbon monoxide poisoning?

No. Sewer gas and carbon monoxide are different substances with different sources and health effects. Carbon monoxide comes from incomplete combustion of fuel (furnaces, cars, fireplaces). Sewer gas comes from decomposing waste in pipes. Both are dangerous, but they require different detection and safety measures.

Is it safe to live in a home with a small sewer gas smell?

A faint occasional smell is usually not an when ready danger, but it signals a problem that will worsen. Have it inspected and repaired. Living with ongoing sewer gas exposure—even at low levels—increases your risk of respiratory problems over time, especially for children and people with lung conditions.