8 Causes of Mold in Your Bathroom—and How to Get Rid of It, According to Experts

Bathrooms are typically the dampest rooms in any home, and despite your best efforts, you may find yourself in a constant battle against mold. That’s because mold only needs two things to grow and spread: water and a porous surface. “Bathrooms are typically moist environments and many surfaces in the bathroom, like tile grout, drywall, wallpaper, shower curtains, even cabinets can allow mold to grow,” says Tony Abate, a certified mold inspector.

Finding mold in the bathroom is more than just an unsightly nuisance. “When moist air in the home promotes the growth of mold and mildew, this can lead to respiratory problems and more serious illnesses,” says Richie Drew, VP of operations at One Hour Heating & Air Conditioning. Identifying and preventing the cause of mold growth is important so can keep your bathroom healthy and clean.

Causes of Mold Growth in the Bathroom

Poor Ventilation

Poor bathroom ventilation is one of the biggest culprits in creating the ideal conditions for mold growth on tile grout, drywall, and wood.

When you’re showering, a lack of airflow creates a high level of humidity. The hot water creates steam, which in turn adds to the moisture in the air. If this is not quickly replaced with drier air from outside the room, it can lead to condensation and prolonged humidity in the space, explains Michael Rubino, a mold and air quality expert. Since some species of mold can grow when the humidity is 60% and above, he says the goal is to keep humidity below that level.

Cracks

Another cause of mold is cracks in grout or caulk, which may be caused by aging material or some type of impact. Rubino says cracks allow for moisture to become trapped for prolonged periods of time. “Mold can grow within 24 to 48 hours, providing a source of moisture and organic material, so cracking provides the perfect opportunity,” he explains.

Misaligned Tiles

In addition to issues with grout or caulk, if the tiles themselves are misaligned, that’s another potential source of mold. “This also allows for trapped moisture from bathing or using the sink, allowing for microbial growth to develop,” Rubino says.

Leaks

A leak anywhere in your bathroom could also be problematic. “If leaks occur under the sink, under the toilet, or around the shower or tub, they can lead to either a massive water event that needs to be completely dried out in 24 hours, or a small, steady source of moisture that goes undetected for some time,” Rubino says. And as bad as a massive water event seems, the small, steady source of moisture is more problematic—he says it can continue undetected for a while, which will allow mold to colonize and thrive.

Poorly Sealed Windows

If your bathroom windows are not sealed properly, Rubino says this will allow outdoor precipitation or humidity to come inside, which creates an opportunity for microbial growth.

Wet Items

Failing to hang up wet items so they can dry is another contributing factor to mold growth in the bathroom, says Rubino. This could include your bath towels, hand towels, or even your shower mat.

Lack of Cleaning

Cleaning is an important defense against mold. So, if you aren't regularly cleaning bathroom fixtures like the showerhead and sink faucet, that could be another cause of mold, Rubino says.

Flooding

It should come as no surprise that an abnormal excess of moisture in the bathroom is problematic. “Flooding, which could be from a leak or a major weather event, like a hurricane, creates a source of moisture for microbial growth,” Rubino says.

How to Remove Mold

For non-porous surfaces, like sealed countertops, Rubino recommends spraying a botanical cleaner on the surface (he recommends Benefect Decon 30), allowing it to sit for 30 seconds, and then wiping it with a microfiber towel. Repeat the process at least three times to ensure all contaminants are removed.

Semi-porous surfaces can be trickier to clean, Rubino says, because the mold roots will have grown into the surface and will be difficult to remove completely. "Abrasive methods combined with products like hydrogen peroxide should be used to remove the roots, and then a sealant should be used after remediation,” he says.

Keep a close eye on the surface to see if the mold returns. “If it returns quickly, the colony could have permeated deep beneath the surface, or there could be a larger problem elsewhere in the home.” Either way, you can attempt to remediate it again, but Rubino says it may be time to call a professional or entirely replace the surface or item. “It’s best to contact a mold inspector and remediation company for larger remediation projects," he explains. "Also, it's typically best to call professionals if mold is in an area like the bathroom ceiling."

For porous surfaces like a shower curtain, Rubino recommends removing and replacing it. “The contamination can exist deep within the fibers and be nearly impossible to remove completely,” he explains.

After the remediation process, you need to deep clean the bathroom to eliminate particles like spores or mycotoxins. “When the [mold] colony grew, it released these tiny particles that are so small they can become airborne and settle throughout space," Rubino says.

When cleaning mold yourself, Rubino always recommends wearing personal protective equipment to avoid inhaling aerosolized particles and prevent cross-contamination.  

Why Does Mold Keep Coming Back?

You may have cleaned mold away in your bathroom, but noticed it rearing its ugly head again and again. “You can clean mold growth using a bleach based cleaner, but if you don’t get to the source of the problem, it will keep coming back and may spread to where you cannot easily clean, like behind the walls,” Abate warns.

Rubino agrees and adds that mold will return for a few reasons. To use a gardening analogy, he says mold is like a weed, and you have to pull it up by the roots to completely eradicate it. If you leave some behind, Rubino says that the colony can come right back.

How to Prevent Mold From Returning

Here are some best practices for preventing mold in your bathroom:

• Use the bathroom fan any time you’re in the bathroom, and let it run for at least 15 or 20 minutes after a shower. If your don't have a fan in your bathroom, try opening the window or bathroom door to create more airflow.
• “Be sure to wipe down all wet surfaces after a shower, and if you use a shower curtain, you should let it dry out to avoid mold growth,” Abate says.
• Abate also recommends using a bleach-based cleaner in the bathroom and cleaning the space regularly to prevent mold growth on those cleaned surfaces.
• Clean and seal your tile grout. “Tile grout that gets wet can grow mold if it’s not sealed correctly, so if you’re not sure or it’s been years, clean the grout well with a bleach cleaner and use a grout sealer to seal it,” Abate advises.
• Check the caulking around your tub, or shower pan, or the sink—anywhere you have gaps that can get wet. “And if that caulk is discolored, remove and re-caulk, which is a small but important protection to keep water from getting behind surfaces where mold can grow and can lead to a costly remediation,” Abate says.

If you keep having mold issues in your bathroom despite these practices, there are whole-home dehumidifiers you can purchase that may come in handy. However, Drew notes that a well-maintained central air conditioning system should cover most of your moisture issues. “If your hygrometer tells you that you need help in damp areas like bathrooms, you can also buy a portable [dehumidifier], but take care to size it to your space and dampness level,” he advises.

Abate also recommends upgrading your air purification system with bi-polar ionization technology. “BPI tubes, added to your home's HVAC system, can kill active mold spores in the bathroom,” he says.

If a faulty fan is to blame for stagnant air in your bathroom, then Abate says it's best to inspect and repair your existing exhaust fan or install a new one. "In a moisture-rich place like a bathroom, these are a necessity,"

If you’re seeing repeated mold in the bathroom and other rooms as well, Drew recommends getting your air ducts professionally cleaned. “Check to make sure vents in the bathroom are not restricting airflow, as air needs to circulate in order to prevent mold,” he says.

You can also check your exhaust fan to see if it’s positioned correctly. Abate says it should be vented outside of your home. “If the moist air from the fan goes into your attic or just up in a ceiling, that will eventually foster mold growth, which would require a large-scale costly remediation,” he warns.

If you're still struggling to identify the cause of your mold issues, Drew recommends consulting an HVAC expert. “A local heating and air professional can help identify the source of poor ventilation and find the most helpful solution to ensure bathroom air is flowing and mold is kept at bay,” he says.