How to Prevent Mold in a Bathroom

David J. Allen

I spent the better part of 2 ½ years learning about mold and indoor air quality because my child's life depended on it. Now I help others avoid ever having to experience the same thing. The mold industry suffers from conflicting opinions and I do my best to distill loads of data into something practical and useful. I love hearing from and helping readers. • "A house desecrated by mildew, mold, or fungus would be a defiled place to live in, so drastic measures had to be taken." — Leviticus 14:45

Of all of the rooms in a home, bathrooms are among the most prone to mold.

Their close quarters, tight spaces, pipes running to and through them, and the volume of water used in them—in the toilet, at the sink, and in the tub or shower—makes them a prolific breeding ground for mold.

This is particularly true if the bathroom is in an apartment or leased property, an old home, was poorly constructed, lacks windows that can be opened to the outside, and if it also houses a shower.

Poor construction—as far as mold in a bathroom is concerned—includes such things as:

  • Particle board, plywood, or non-laminates installed below sinks
  • Caulk lines in the tub or shower that are incomplete or allow for a build up of water that doesn’t run off of them
  • Carpet flooring
  • Faulty pipe connections or leaky drains
  • Wallpapered walls
  • Flimsy vinyl baseboards with gaps atop them
  • Gaps or cracks in the grout between tiles or along the edges of the room.
  • Lack of a ceiling-mounted ventilation fan and/or lack of a window that opens to the outside also contribute to a mold-prone bathroom.

Why mold grows in bathrooms

Mold requires four primary components in order to grow—mold spores, acceptable temperatures, a food source, and considerable moisture—and all four of them can be prevalent in a bathroom.

  • The first, mold spores, are everywhere. Removing them all is impossible, barring herculean efforts and laboratory-style clean rooms.
  • The second, acceptable temperatures, are likewise virtually everywhere and are often difficult to control. Mold appreciates many of the same temperatures that humans find either enjoyable or bearable, and thrives in warm, moist (humid) spaces.
  • The third, a food source for mold, is also virtually everywhere. If mold can’t permeate and consume parts of a surface itself, more often than not, there is a film or build up on the surface that mold can consume—soap scum, a hand print, dirt or grime, etc.
  • The fourth, considerable moisture, is the easiest to manage, control, and prevent inside of a building. The control of moisture is and should be the primary focus of mold prevention.

In a bathroom, heat from the shower combines with the moisture of steam and running tap water to create the humid environment that mold thrives in. The absence of UV light—and the relative darkness that bathrooms often sit in—also help provide the perfect environment for mold growth.

Poor air circulation and a build-up of organic matter in hard-to-reach areas also helps mold spores come to life if they aren’t caught early and cared for quickly.

With that in mind, there are some relatively simple steps that can be taken to prevent the majority of  visible mold from most bathrooms.

In short:

  • Keep it dry
  • Keep it clean
  • Keep the air flowing

Bathrooms that are most prone to mold

Knowing that mold appreciates damp and poorly ventilated environments, we see that some bathrooms would be more prone to mold than many other rooms. Bathrooms with the highest humidity levels, the dirtiest surfaces, and the poorest airflow will, generally speaking, have the worst problems with mold.

10 Ways to Prevent mold in a bathroom

If done diligently, the following very simple steps will help you prevent mold growth from occuring in a bathroom.

1. Leave the ceiling fan on after showering

Showering producers steam and condensation, which should be removed from the bathroom through a ceiling fan. Run the bathroom fan for 30 to 60 minutes after showering to reduce the likelihood of mold growing.

The bathrooms in a residence or office building are usually legally required to have either a window or a ceiling fan for this very purpose.

“Bathroom fans are also recommended to remove excess moisture during periods when it is being generated by bathing or showering.”

UCF, FSEC Energy Research Center, “Mold Growth”

2. Open the bathroom window

If your bathroom has a window, leave it open as long and often as possible, weather permitting. This alone will usually provide enough air flow to make bathroom mold a non-issue.

3. Dry surfaces off after use

Dormant water is likely to lay in dips, depressions, and crevices between a shower’s floor tiles. The ledges of tubs and the caulk line between the tub and tiles is another spot.

Whether you opt to go through the admittedly annoying process of drying these spots off daily is your prerogative, but it’s helpful to know that if mold becomes more of a concern, this is one of the most effective ways to combat it.

4. Fix leaks and ensure drains work well

Pipes and drains beneath the vanity or sink are a common hotbed for mold growth. Leaky pipes and clogged drains often occur together. You’ll want to report leaks to your building manager and act quickly to ensure the leak is stopped and that any water has been thoroughly removed.

In some cases, rotted or water-logged wood or fiberboard will need to be taken out and replaced during mold remediation.  

5. Clean well and routinely

There are plenty of options beyond bleach that can be used for cleaning mold. Bleach isn’t typically advised, however if it is all you have it can be used on non-porous surfaces only: The tiled shower walls, the shower floor, the tub, and the toilet, but not on drywall, wood, or particle board. 

“Clean bathrooms with mold-killing products.”

U.S. CDC, “You Can Control Mold”, July 17, 2020

6. Spread out damp fabrics

Used washcloths, towels, sponges, loofahs, and similar items should be spread out as far as is feasible and left to dry fully. The ceiling fan should be run while these are drying, to give the moisture somewhere to go outside of the bathroom.

This applies to slightly damp washcloths and towels, not to sopping wet ones, which should not be hung in the bathroom, even if a fan is running.

7. Hang wet clothing outside

Dripping and evaporating water from wet clothes should be dispersed into the ground and air outside of your house or apartment.

If you must hang wet clothing in the bathroom, position it entirely over the shower or bathtub and leave the fan on and windows and door open for maximum air flow and circulation.

8. Store toiletry bottles on a wire shower rack

The water that accumulates on shampoo and conditioner bottles, soap dishes, and other bathing products should be allowed to easily run off of these items.

A wire-frame rack or shelf is one of the easiest ways to allow that run-off to occur. Wet bottles left on flat surfaces and ledges will rarely dry fully between uses, contributing to the possibility of mold growth over time.

9. Optional: Run a dehumidifier

It should not typically be necessary to have a dehumidifier running all day in a home or apartment bathroom.

Between windows that can be opened to the outside, and a ceiling fan, enough of the moisture in the air should be able to be removed to make mold growth not a concern.

In some cases, however, a dehumidifier may be a good idea or may even be necessary. In each of the following examples, the use of a dehumidifier in the bathroom could make sense:

  • Numerous people use the shower (extending the time during which the room is hot and wet, or humid.
  • The ceiling fan is briefly not working.
  • Outdoor weather makes opening a bathroom window not practical or unsafe (rain, snow, strong winds).
  • If a leak has recently occurred.