Mold Growing in the Toilet? Here’s What It May Mean

Michael Rubino

November 7

Chances are that most, if not all, of the world’s population has dealt with mold in the bathroom a time or two. Whether in the bathtub, grout, or sink, this room is on the top of this list for that fungus among us to pop up and begin growing. With all of the moisture involved in these washrooms, it makes sense! But what about mold growing in the toilet? 

Is that yet another common occurrence that can be chalked up to a typical issue, or does it mean something more?

The answer is: it depends. What many don’t know is that mold growing in the toilet can be a key indicator of a contamination situation occurring in the home, depending on where the growth is. 

Understanding why this is a sign and what to do if it happens in a home can be an essential part of any home health plan. Here’s what you need to know. 

But First, Mold

Before getting into the toilet aspect, it’s important to understand the contaminant in question. Aka, mold. 

Mold is a type of fungus with over 100,000 species identified by researchers so far. Each species reproduces by releasing microscopic particles called spores into the surrounding environment.¹’² It’s similar to how a dandelion releases those fluffy, white seeds, except spores are invisible to the naked eye.


These tiny particles will remain in spore form until they land on a surface with the right elements for growth. Thanks to its hardy nature, a spore typically only needs two main components to transition into a living colony.³ 

These two components are: 
  1. A food source
  2. A moisture source

If these are present for 24-48 hours, that spore will put down roots called hyphae and begin colonizing the area. The reproductive cycle will also start up, releasing more spores into the surrounding area in hopes of finding another habitable surface. 

The Toilet Aspect

Going off of the information above, it’s pretty easy to see how some instances of mold growing in the toilet can occur. 

For food sources, there are all sorts of organic matter floating around, like skin cells and other particles kicked up while using the bathroom. Tack on the mineral buildup from the water used in the system, and this is an easy box to check off.

As for moisture, this is a given in this specific fixture. Water is contained both in the tank and the bowl, creating a perfect opportunity for microbial growth. Not to mention, the bathroom itself is full of moisture. From steamy showers, wet towels and bathmats, running sinks, and flushing toilets, there’s an endless source of wetness in this room. 

Basically, if a lucky mold spore lands inside the toilet, it will think it won the lottery. Once established, this fungus among us can begin to cause a range of problems that can impact our health. 

Is Mold Growing in the Toilet Dangerous?

As mentioned above, when mold grows, it releases microscopic spores into the surrounding space. Some species of mold also create microscopic toxins called mycotoxins when threatened, further adding to the particle party.⁴ Interestingly, while mycotoxins are regulated in our food products, no limits exist for acceptable levels in our homes.⁵ 

And, on top of all of that, bacteria can often grow in the same conditions as mold.⁶ This adds yet another complex layer to the contamination situation going on in the tub. 

The ability of these particles to cause problems largely rests on their size. Measured in a unit called a micron, mold spores, fragments, mycotoxins, and bacteria can all be inhaled, ingested, and absorbed into the body.⁷


The EPA further classifies these types of particles as particulate matter and breaks them down into two categories.⁸ 

These two categories are:
  • PM10: particles that have a diameter of around 10 micrometers or less.
  • PM2.5: fine particles that have a diameter of around 2.5 micrometers or less.

A common misconception is that since mold is everywhere, it’s not a big deal when it grows inside a home. That is not true

Yes, we are exposed to all of these particles throughout our regular day while driving down the street, walking into work, and even hanging out in our homes. As we can’t put a bubble around ourselves or our indoor environments, it’s impossible to completely avoid coming into contact with some of the particles floating around. When this typically occurs, the body will tag these particles as foreign invaders and send the immune system to kick them to the curb ASAP.

An indoor contamination situation is not the same scenario. Thanks to modern building practices pushing for net-zero energy efficiency, there’s very little airflow between indoor and outdoor environments. So, while particles from a mold colony outdoors have the entire world to disperse through, a majority of those from a colony indoors only have that enclosed space to blow around. The longer that contamination situation exists indoors, the more particles will build up in the room and the rest of the home as well.


  • Lowers the indoor air quality
  • Contaminants the surfaces within
  • Increases the chances of another colony developing elsewhere in the home

Now, instead of a few particles here and there throughout the day, the body is tasked with fighting off an entire army of them. This can lead to the immune system getting bogged down and/or malfunctioning, opening the door to chronic symptoms.⁹’¹⁰’¹¹’¹²’¹³ It can also allow autoimmune conditions to develop, such as Aspergillosis, Mast Cell Activation Syndrome, or Chronic Fatigue Syndrome

Some common symptoms of mold exposure include:
  • Headaches and migraines
  • Joint and/or muscle pain
  • Digestive issues
  • Brain fog
  • Chronic fatigue 
  • Flu and cold-like symptoms
  • Hair loss
  • Anxiety and/or depression 
  • Mood swings 
  • Skin issues such as rashes
  • Hormone imbalances

The tricky thing is that no two people will respond the same way to a situation such as mold growing in the toilet. One individual may experience occasional brain fog while another develops a dozen symptoms and an autoimmune disease. 

Much more research is needed to better understand how indoor contaminants affect our health, but it’s a tough subject to nail down. Factors such as genetics, mold species, mycotoxins, bacteria, length of exposure, and immune system status all play a role. Those with compromised or developing immune systems, for instance, are at greater risk of developing symptoms faster and to a greater extent. 

The potential for adverse health reactions is reason enough to want to avoid mold growing in the toilet and in a home, in general. 

Why is Mold Growing in the Toilet?

That’s the key question! The answer depends on where the growth is. 

The Bowl

This can be a common issue for toilets that are infrequently used and cleaned. A spore can zip right in through the opening between the bowl and the seat and begin to grow thanks to the water and organic matter present. 

The Tank

mold growing in the toilet

This is the key location to look out for. When it comes to the toilet tank, the lid is heavy, but it’s not hermetically sealed. That’s pretty much a fancy way of saying that it doesn't allow for much air exchange. If mold starts growing inside the tank, that typically means there are enough spores in the indoor air that some were opportunistically able to get into this location. 

While it’s not impossible for a lucky spore to make it inside the toilet tank, it’s far more likely that a mold colony elsewhere is pumping spores into the indoor air. That’s why this location can indicate a contamination situation elsewhere in the home, and why it’s a phenomenal trick to determine if there’s a potential hidden problem.

How Do You Know If There’s Mold Growing in the Toilet?

Knowing what signs to look out for can help ensure that your bathroom isn’t bogged down with microscopic particles. 

What Does Mold Growing the Toilet Look Like?

With so many species existing in the world, mold colonies can come in a variety of colors, shapes, and textures. Some of the most common colors include green, white, grey, blue, red, black, brown, or a combination of them. As for textures, they could be fuzzy, powdery, velvety, or slimy.

If any type of unidentifiable growth pops up, it's a safe bet to assume there’s a mold problem. So, grab a flashlight and take a close look at the bowl (including the underneath rim), the seat, the tank lid, and the inside of the tank.

mold growing in the toilet

Other aspects to look out for include:

  • Murky water
  • Particles floating around in the water
  • Rings around the tank or bowl

What Does Mold Growing in the Toilet Smell Like?

Mold growth isn’t always visible. It could be in a hidden crevice or in the pipes. In this instance, look to your nose to help determine if there’s a problem.

Growing mold often creates an earthy, musty, damp, cigar-like smell due to the release of gases called microbial volatile organic compounds (MVOC).¹⁴ If this odor is coming from the toilet or the water, it points to a problem.

Do You Feel Weird After Using the Bathroom?

Our bodies are incredible warning systems that will alert us if something’s wrong, including if there’s a contaminant in our indoor environments. It’s up to us to listen to these signals and figure out what the root cause is so that it can be eliminated.

If chronic symptoms spark up out of the blue and seem to get worse while in the bathroom, this can be your body’s way of saying, “Hey, something is definitely not right here.”

What Do You Do If You Find Mold Growing in the Toilet?

If it’s in the bowl, you can jump straight into deep cleaning the fixture to eliminate the contamination. If it’s in the tank, you can opt for this step as well, but remember that this location can indicate an underlying problem elsewhere in the home.

That being said, if you find mold growing in the toilet tank, grab a flashlight and carefully go through every nook and cranny in the building.

Mold hotspots include:
  • Basement 
  • Attic
  • Windowsills and door frames
  • Crawlspaces
  • Appliances 
  • Underneath the sinks 
  • Bathroom
  • Kitchen

If you don’t see anything obvious, that doesn’t always mean that there’s no problem. You could have a hidden leak somewhere, like in the walls or flooring, that’s allowing mold to grow. If you suspect a problem or are having chronic symptoms, it’s best to hire a qualified mold inspector

inspecting home

This individual will spend hours going through the home and utilizing a variety of testing methodologies to determine what’s going on inside the home and if there’s a contamination problem. The more thorough they are, the better.

Data you should expect to see include:

  • Types of molds present
  • Quantities of each mold species
  • Potential spore presence in the HVAC system 
  • Presence of mycotoxins 
  • Presence of bacteria

From there, you’ll have a clear picture of whether there’s an issue and what steps need to be taken to solve the problem if it exists.

If you’re not quite ready to call in an inspector, consider opting for an at-home testing kit such as The Dust Test. This can help determine if there’s a potential contamination situation within the home. 

How Do You Get Rid of Mold Growing in the Toilet?

The key to getting rid of mold growing in the toilet is to be as thorough as possible. In order to properly remediate that fungus among us, all contamination must go, including the colony, roots, dead mold particles, mycotoxins, and bacteria. Just because you can’t see the particles or roots, doesn’t mean that they’re not there!

Exposure will continue if any microscopic particles are left behind, which is a health no-no. On the other hand, if roots remain behind, the colony can pop right back up.

Pro tip: Do NOT use bleach to clean the toilet. It leaves particles such as dead mold and mycotoxins behind, leading to continued exposure.¹⁵ You need a product with a surfactant that will pull particles from the surface they’re stuck on so that they can be wiped away. 

mold growing in the toilet
Steps to properly get rid of mold growing in the toilet include:
  • Put on protective gear, including gloves, goggles, and a mask
  • Turn the water supply off by twisting the water control valve 
  • Flush the toilet until the bowl no longer fills and then plunge out as much water as possible
  • Liberally spray a botanical cleaner such as Benefect Decon 30 inside the tank 
  • Allow this to sit for 10 minutes 
  • Wipe it away with a microfiber towel
  • Complete this process two more times, allowing it to sit for 30 seconds before wiping
  • Pour some of the cleaner into the tank and flush
  • Spray the cleaner inside of the bowl and allow it to sit for 10 minutes
  • Use a scrubbing brush and thoroughly scrub the interior of the bowl
  • Repeat the process two more times, allowing it to sit for 30 seconds before scrubbing 
  • Spray the cleaner over the seat and the toilet tank lid 
  • Repeat the same procedure outlined above for the toilet tank
  • Turn the water back on and flush the tank a few times to flush the system with clean water

After you’re finished, deep clean the bathroom using a HEPA vacuum cleaner, botanical cleaning products, and microfiber towels to remove any contaminants created by the current mold colony. 

If the mold pops right back up, it could indicate a problem elsewhere in the home that requires a professional. The best option is to hire a qualified professional to come in and inspect the home to get a clear picture of what’s causing mold growing in the toilet. If you’re not quite ready for this step, consider opting for an at-home testing kit such as The Dust Test.

How Do You Prevent Mold Growing in the Toilet?

The best way to deal with mold growing in the toilet is to prevent it from popping up in the first place. The more you can do to stop this fungus among us from moving in, the healthier the indoor environment will be.

prevent mold growing in the toilet
Steps to prevent mold growing in the toilet include:
  • 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

So Fresh and So Clean

healthy home

The average person breathes 20,000 breaths per day and spends around 90% of their time indoors. The state of these indoor spaces matters. If they’re filled with contaminants such as mold, mycotoxins, and bacteria, that will negatively impact our health. 

Properly handling mold growing in the toilet is an important piece of home health. Not only is it a health hazard, but it can also indicate a larger contamination situation elsewhere in the home. Adding this fixture to your home maintenance and hotspot checklist can help keep your indoor environment in tip-top shape and ensure it’s supporting your wellbeing.

Health beings at home.™


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