It’s safe to say that nearly everyone has encountered mold in the bathroom at some point. From bathtub grout to sink crevices, the bathroom tops the list of places where mold tends to thrive. With the constant moisture found in this room, it’s no surprise! But what about mold growing in the toilet?

Is this just another common occurrence to shrug off, or could it be a sign of something more significant?

The answer? It depends. Mold in the toilet can sometimes signal a larger issue of contamination in the home, depending on where the mold is located.

Understanding why mold might be a red flag and what steps to take if it appears can be a key part of maintaining a healthy home. Let’s dive in.

Let’s Talk Mold

Before focusing on the toilet, it’s essential to understand mold itself.

Mold is a type of fungus, and scientists have identified over 100,000 species so far. These fungi reproduce by releasing microscopic particles called spores into the air. Think of it like how a dandelion releases its fluffy white seeds—except mold spores are invisible to the naked eye.

These spores remain dormant until they land on a surface that meets their needs for growth. Thanks to mold’s resilient nature, a spore typically requires just two main ingredients to develop into a living colony:

1. A food source
2. A moisture source

If these elements are present for 24-48 hours, the spore will sprout roots called hyphae and begin colonizing the surface. From there, the reproductive cycle starts, and more spores are released into the environment, searching for new surfaces to colonize.

Why Toilets Are a Target

Given the information above, it’s easy to see why toilets can sometimes harbor mold.

Food Sources

Toilets provide an array of organic matter, such as skin cells and particles from everyday bathroom use. Additionally, mineral buildup from water systems can also act as a food source for mold.

Moisture Sources

Moisture is a given with toilets. Water sits in both the bowl and the tank, and the bathroom itself is a moisture hotspot thanks to steamy showers, wet towels, and running sinks.

When a mold spore lands inside a toilet, it’s like hitting the jackpot. Once established, the mold can begin to impact indoor air quality and potentially your health.

Is Mold in the Toilet Dangerous?

As mold grows, it releases spores into the surrounding environment. Some mold species also produce microscopic toxins known as mycotoxins when threatened. These particles can be inhaled, ingested, or absorbed into the body, contributing to a host of potential health problems.

The U.S. Environmental Protection Agency (EPA) classifies these particles as “particulate matter” and divides them into two categories:

1. PM10: Particles with a diameter of 10 micrometers or less
2. PM2.5: Fine particles with a diameter of 2.5 micrometers or less

While it’s true that mold spores are present in our daily environments, indoor mold growth introduces a unique challenge. Modern buildings are designed to be energy-efficient, which limits airflow between indoor and outdoor environments. This means that spores from an indoor mold colony have nowhere to escape and accumulate over time, leading to:

• Lower indoor air quality
• Contaminated surfaces
• Increased chances of mold colonies developing elsewhere in the home

Over time, exposure to elevated mold levels can overwhelm the immune system, potentially leading to chronic symptoms or triggering conditions such as Aspergillosis, Mast Cell Activation Syndrome, or Chronic Fatigue Syndrome. Symptoms of mold exposure may include:

• Headaches or migraines
• Fatigue
• Brain fog
• Joint or muscle pain
• Digestive issues
• Anxiety or depression
• Skin rashes
• Hormonal imbalances

The severity of these symptoms varies widely between individuals, depending on factors such as genetics, immune system status, and the specific mold species involved.

Why Is Mold Growing in the Toilet?

The location of the mold growth can reveal a lot about the root cause.

The Bowl

Mold in the toilet bowl is often due to infrequent use or cleaning. Spores can settle and grow in the water and organic matter present.

The Tank

Mold in the toilet tank is more concerning. The tank’s heavy lid limits airflow, creating a sealed environment. If mold grows here, it’s often a sign that there are high levels of mold spores in the home’s air—potentially from a hidden mold colony elsewhere.

How to Identify Mold in the Toilet

There are multiple ways to determine if there’s mold in the toilet. 

Appearance

Mold colonies can vary widely in color, including green, black, white, grey, blue, and more. Textures may range from fuzzy and powdery to slimy and velvety. Look closely at the bowl, the rim, the tank lid, and the inside of the tank for any unusual growths.

Smell

Mold often produces an earthy, musty odor due to the release of microbial volatile organic compounds (MVOCs). If your toilet or bathroom smells musty, it could indicate hidden mold.

Physical Symptoms

If you experience symptoms like headaches, fatigue, or brain fog that worsen after using the bathroom, your body might be signaling a mold problem.

What to Do If You Find Mold

Handling mold in the toilet will depend on where you find it. 

In the Bowl

For mold in the bowl, a deep clean should suffice. Use a botanical cleaner with a surfactant, such as Benefect Decon 30, to remove all traces of mold and its roots.

In the Tank

If mold is in the tank, it’s wise to inspect the rest of your home for mold hotspots, such as:

• Basement
• Attic
• Crawlspaces
• Under sinks

If no obvious issues are found but symptoms persist, consider hiring a qualified mold inspector. They’ll use testing methods to identify mold species, mycotoxin presence, and contamination levels. Alternatively, you can use an at-home testing kit, like The Dust Test, for preliminary insights.

How to Remove Mold from the Toilet Tank

Follow these steps to thoroughly clean and eliminate mold:

• Wear protective gear (gloves, goggles, and a mask).
• Turn off the water supply and flush the toilet to empty the bowl.
• Spray a botanical cleaner inside the tank and bowl, letting it sit for 30 seconds.
• Scrub thoroughly with a brush and wipe surfaces with a microfiber towel.
• Repeat the process to ensure all mold and particles are removed.
• Deep clean the bathroom using a HEPA vacuum and botanical cleaners to remove lingering particles.

The ultimate goal is to ensure all contamination, including the roots of the mold, is gone.

How to Prevent Mold in the Toilet

The best way to tackle mold is to prevent it from growing in the first place. Here are some tips:

• Deep clean the bathroom regularly: Using a HEPA vacuum cleaner, botanical cleaning products, and microfiber towels, give this washroom a thorough cleaning once a week (including the toilet bowl!). Also, make sure to throw all porous items in the wash with a product such as EC3 Laundry Additive to help remove microscopic particles present on the items. This should include the bath mat, towels, washrags, and potentially the shower curtain and liner. 
• Clean the toilet tank twice a year: This will remove any mineral buildup and particles that could allow for microbial growth.
• Keep everything dry: This includes wiping up pooled water, hanging up towels and bathmats to dry, squeezing the shower after use, and separating the shower curtain and liner.
• Focus on airflow: Some species of mold can grow in high humidity. To prevent this, maintain indoor humidity levels of 35-50% by creating airflow.¹⁵ To achieve this, turn on the exhaust fan while bathing and crack a door or window. If this level just will not go down, consider investing in a dehumidifier for the space. 
• Fix leaks ASAP: Remember, mold can grow in as little as 24-48 hours. Resolving water damage quickly and properly drying out the space will help reduce the opportunity for this fungus to begin growing. 
• Regularly check hotspots: The sooner you catch a problem, the better. It can reduce the contamination present and help prevent other issues (such as mold growing in the toilet tank) from popping up. Areas to check include: 
  • Appliances
  • Windowsills and doorframes
  • Underneath sinks
  • Attic
  • Basement
  • Crawlspaces
  • Grout and caulk

A Healthier Home Starts Here

The average person takes about 20,000 breaths daily and spends 90% of their time indoors. Maintaining clean, contaminant-free spaces is vital for overall health. Addressing mold in the toilet and elsewhere in the home helps ensure your indoor environment supports your well-being.

Citations:

• Environmental Protection Agency. (n.d.). Mold. EPA. Retrieved from https://www.epa.gov/mold.
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• Lstiburek, J., Brennan, T., & Yost, N. (2002, January 15). Rr-0208: What you need to know about mold. Building Science Corporation. Retrieved from, https://www.buildingscience.com/documents/reports/rr-0208-what-you-need-to-know-about-mold/view.
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