Why Shower Mold Keeps Coming Back (and the Habits That Stop It)

The one-time cleanup

1. 1

   Get air moving and gear up

   Turn on the bathroom fan and open a window if you have one. Put on rubber gloves, goggles without vent holes and an N-95 mask, which is the gear the EPA lists for mold cleanup.

2. 2

   Mix soapy water

   Squeeze a little dish soap into a bucket of warm water and swish it around. The EPA’s advice for mold on hard surfaces is plain detergent and water, so you do not need anything stronger.

3. 3

   Scrub the spots

   Dip a grout brush or the soft side of a non-scratch sponge in the soapy water and scrub each spot in short strokes. Work from the top of the wall down, so the dirty water runs over parts you have not done yet. Dump the water and mix fresh if it gets murky.

4. 4

   Rinse with plain water

   Rinse the walls with plain water from the shower head or a cup, and keep going until no more suds run down the tile.

5. 5

   Dry it completely

   This step is the whole point. The EPA’s direction is to scrub mold off hard surfaces and dry them completely. Squeegee the walls, wipe the corners and ledges with an old towel, and leave the fan running.

   What it looks like when it is done: no standing drops on the ledges or in the corners.

6. 6

   Look at what is left

   Check the grout and the caulk in good light. If the grout still looks dark, see How to clean grout without ruining it.

   A dark mark inside the soft caulk is a different problem. The EPA says not to caulk over moldy surfaces, so see How to get mold stains off shower caulk.

The habits that keep it from coming back

The cleanup takes the mold off. These habits take away the water it needs to grow back.

1. Run the fan during your shower and at least 20 minutes after. Fan maker Broan-NuTone cites the Home Ventilating Institute for that 20 minutes. The Department of Energy’s building guide recommends one hour, with a timer switch so the fan shuts off by itself. Have an electrician put the switch in.
2. Make sure the fan really vents outside. The Department of Energy’s guide says a bathroom fan should vent outdoors, not into the attic, a crawlspace or the space between floors.
3. Squeegee or wipe after every shower. DreamLine, a shower door maker, tells owners to wipe glass and acrylic walls after each use. On tile, a squeegee or towel does the same job.
4. Leave the door open. For damp surfaces, the EPA suggests more air movement by opening doors and windows when you can.
5. Watch the humidity. The EPA says to keep indoor humidity below 60 percent, ideally 30 to 50 percent, and that an inexpensive meter can measure it.
6. Fix drips fast. The EPA says to fix plumbing leaks as soon as possible and to dry wet areas within 24 to 48 hours.
7. Clean more often. For mold that keeps reappearing in a shower, the EPA says more ventilation and more frequent cleaning will usually stop it, or at least keep it to a minimum.

When it will not work, and what to do instead

Sometimes the spots come back even after you change your habits. Here is what to check.

• It comes back in the same spot within days. That spot is staying wet. Look for a drip, a leaky door seal or a ledge where water pools, and fix the water first.
• You want to use bleach so it never comes back. It makes sense to reach for the strongest bottle under the sink. But the EPA says bleach is not recommended as a routine part of mold cleanup. Drying the shower is what stops the regrowth.

Why it works

Mold spores float through the air indoors and out, and the EPA says it is impossible to get rid of all of them. That sounds worse than it is, because spores are only half the story.

The other half is water. The EPA says no type of mold will grow without water or moisture, and that mold is usually not a problem indoors unless spores land on a wet or damp spot.

If the shower walls stay damp for hours, the spores that land there get what they need, day after day. Think of them like seeds: you cannot keep every seed out of a garden, but nothing sprouts in dry dirt.