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Can Sewer Gases From a Backup Be Dangerous to Breathe?

Last updated October 26, 2026

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The short answer

What Is in Sewer Gas

Sewer gas is a mix of several gases produced by decomposing waste. The main components include hydrogen sulfide, which smells like rotten eggs, methane, ammonia, and carbon dioxide. Each of these gases can affect your health differently, and the risk depends on how long you breathe them in and how concentrated they are.

Hydrogen sulfide is the most concerning because it can irritate your eyes, nose, and throat at low levels. At higher levels, it can cause serious breathing problems or even be life-threatening. Methane is not toxic by itself, but it can replace oxygen in a confined space, making it hard to breathe. Ammonia can also irritate your airways and lungs.

Short-Term Symptoms to Watch For

If you are exposed to sewer gas, you might notice a headache, dizziness, or nausea within a short time. You could also feel tired, have a sore throat, or experience coughing. These symptoms often go away once you get to fresh air, but they can be more serious if the exposure is long or the gas is strong.

Young children, older adults, and people with breathing conditions like asthma may be more sensitive to sewer gas. If you or someone in your home feels unwell after smelling sewer gas, move outside and see a doctor if the symptoms do not improve. Do not go back inside until the area has been aired out.

  • Headache and dizziness
  • Nausea and vomiting
  • Eye, nose, and throat irritation
  • Coughing or trouble breathing
  • Fatigue or confusion

Long-Term Risks of Breathing Sewer Gas

Breathing low levels of sewer gas over a long period can cause more serious health problems. Prolonged exposure to hydrogen sulfide may damage your nervous system or lead to chronic breathing issues. Repeated exposure to ammonia can also harm your lungs and airways, especially if you already have a respiratory condition.

The risk increases in confined spaces like basements or crawl spaces where gas can build up. If a backup has left standing water or waste, the gas can keep forming until the mess is cleaned and dried. Acting quickly to address the source is important for protecting your health.

How to Protect Your Family

If you notice a strong sewer smell, open windows and doors to let fresh air in. Turn off any heating or cooling systems that might pull the gas further into your home. Leave the area until the smell clears, and do not run fans that could spread the gas to other rooms.

Avoid touching or cleaning up sewage without proper protection. Wear gloves, boots, and a mask if you must go near the area. For a major backup, local water damage pros can handle the cleanup safely and thoroughly. They have the right equipment to remove waste and dry the space.

When to Bring in the Pros

A sewer backup that leaves visible waste or a strong, lingering smell is not a do-it-yourself job. The pros can remove contaminated materials, clean surfaces with proper disinfectants, and dry the area to prevent mold. They also have air monitoring tools to check that gas levels are safe again.

If the backup is small and you clean it yourself, use bleach or a disinfectant designed for sewage. Dry everything completely within 24 to 48 hours to reduce the chance of mold growth. For larger areas or if you feel unsure, call local water damage pros to assess the situation. Policies vary, and your insurer decides what is covered.

  • Strong sewage smell that does not fade
  • Visible waste or standing water
  • Contaminated drywall or flooring
  • Health symptoms in family members
  • Backup affects multiple rooms

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Frequently asked questions

How long does sewer gas stay in a home after a backup?

It depends on the size of the backup and how quickly you air out the space. With open windows and fans, the smell may fade in a few hours. But if waste is left behind, gas can keep forming, so cleaning and drying are key.

Can sewer gas explode?

Methane in sewer gas is flammable, and in very high concentrations, it can ignite. That is rare in a home, but you should not use matches, lighters, or other open flames near a backup. Leave the area and let it air out before doing anything else.

Should I call a plumber or a water damage pro?

A plumber can fix the source of the backup, like a clogged pipe or broken line. A water damage pro handles the cleanup of waste, contaminated surfaces, and drying. For a large backup, you might need both, starting with the plumber to stop the flow.

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