Sewer gas is a byproduct of the breakdown of natural human waste. It comprises a mixture of gases, including hydrogen sulfide, ammonia, and more.

The hydrogen sulfide in sewer gas is what gives it its signature rotten egg smell.

Sewer gas isn’t necessarily toxic at low levels. However, chronic exposure, or higher levels of exposure, can cause symptoms of sewer gas poisoning.

In this article, we’ll look at the causes of sewer gas leaks in your home as well as the symptoms, diagnosis, and treatment of toxic sewer gas exposure.

Modern plumbing systems have measures in place to protect homes from sewer gas leakage. There are a handful of possible causes for a sewer gas smell in your home, most of which are the result of plumbing failures.


If there are leaks in your plumbing system due to improperly placed pipes or vents, you may become exposed to sewer gas.

Sewer gas can also leak into your house when plumbing vents are installed too close to a window or air intake.

In some cases, leaks from nearby septic systems can enter your home through cracks in the foundation.

Cracked pipes

Sewer system pipes are reinforced to protect the inside of your home from exposure to the byproducts of human waste. If your pipes are degraded, cracked, or broken, sewer gas can leak through them and into your home.

Blocked air vents

Air vents are responsible for diffusing toxic gases away from your home. If your air vents are blocked, like with dirt, debris, or other items, they may not be able to vent your home properly. This can cause sewer gas to build up in the pipes and leak into the home.

Clogged drains

Like air vents, drains are responsible for the transportation of toxic waste through the septic system. If your drains are clogged from items that shouldn’t have been poured or flushed, it can cause a sewage backup.

If this backup isn’t treated, the clog can continue to decompose and leak sewer gas back into your home.

Dry plumbing

The movement of water through sewer systems helps provide a barrier against potentially harmful gases.

When plumbing systems, such as toilets and drains, aren’t used, they can dry out and lose their water barrier. This can cause the area to become dry, which allows sewer gas to leak into the house.

Loose toilets

Toilets are an important part of the sewer system in your home. To protect yourself from a leakage of gas from the pipes, toilets should always be tightly fitted to the sewer lines.

A loose toilet can cause a gap in the pipes and lead to a leakage of sewer gas into your home.

Sewer gas is a complex mixture of various gases and compounds, some of which are toxic to humans.

The primary components of sewer gas include:

  • hydrogen sulfide
  • methane
  • ammonia
  • carbon dioxide

While sewer gas isn’t dangerous in small amounts, these compounds contribute to sewer gas toxicity at high levels.

Hydrogen sulfide is the primary gas in sewer gas. According to research, hydrogen sulfide has shown to be toxic to the oxygen systems of the body. In high amounts it can cause adverse symptoms, organ damage, or even death.

Ammonia is a well-known compound that’s often used in cleaning chemicals, such as Windex. It has a distinctive odor.

Exposure to ammonia can cause eye, nose, and throat irritation. At higher levels, ammonia is toxic to humans. It can cause organ damage or death.

Methane and carbon dioxide are both relatively nontoxic greenhouse gases. However, in large amounts, methane gas is extremely flammable.

Paired with the flammability of ammonia, this mixture makes high levels of sewer gas a fire hazard.

If sewer gas is present in your home, the first sign you may notice is the smell of rotten eggs. You may also experience various symptoms of exposure, such as:

It’s uncommon to be exposed to high levels of sewer gas at home. However, high levels of sewer gas exposure can occur in industrial workplaces. The symptoms include:

  • loss of smell (you’ll no longer be able to smell the rotten egg odor of sewer gas)
  • mouth, throat, and lung irritation
  • eye irritation and pink eye
  • seizures
  • coma
  • possibly death

According to the Centers for Disease Control and Prevention, there’s no blood test or detection test to determine whether someone has been exposed to sewer gas.

Instead, sewer gas toxicity can be diagnosed if:

  • You’ve noticed the smell of sewer gas.
  • You’re experiencing the symptoms of sewer gas exposure.
  • Your home or workplace has been shown to be exposed to a sewer gas leak.

If there’s only a mild sewer gas leak, the first step for treatment is to air out the house and call a plumber to come and inspect and fix the leak. Getting some fresh air can help reduce your symptoms, too.

Higher levels of exposure to sewer gas require immediate medical attention. Seek medical care right away if you experience any of the following:

  • trouble breathing
  • dizziness
  • nausea
  • other symptoms of high-level exposure
What to do if you smell sewer gas

If you suspect there’s a sewer gas leak in your home, first try to locate where the leak is coming from. Be sure to check all floor drains, toilets, and vents to make sure nothing is cracked, blocked, clogged, or loose.

After you’ve located the source of the leak, book an appointment with a plumber for an inspection. While you’re waiting for the inspection, vent or air out your home. Be sure to keep drains and plumbing air vents clean.

If you believe there’s a sewer gas leak in your home, get in touch with a plumber right away.

A plumber can assess your home for potential leak areas. They can fix the leak and advise you with the best course of action for how to keep your plumbing system functioning properly.

Sewer gas is a common byproduct of our modern septic systems. Leaks, cracks, or blockages in the plumbing can cause sewer gas to leak into your home.

The best remedy for a minor sewer gas leak is to call a local plumber so they can find and fix the leak.

The symptoms of sewer gas exposure are mild and will go away after exposure ends.

However, if you suspect a sewer gas leak and are also experiencing symptoms of high-level exposure, seek emergency medical attention and an emergency plumber right away.