How to Remove Black Mold from Shower Caulk and Grout

Black mold in the shower — those dark spots along the bottom, in the corners and along the tub edge — is one of the most common household mold problems. They’re usually not dangerous “toxic black mold” — they’re common surface molds that thrive on soap residue and daily moisture. Still, they look bad, can bother people with allergies or asthma, and won’t go away without a change in routine.

Not sure it’s mold at all? Our guide to mold vs mildew explains the difference.

What you’ll need

• Gloves (nitrile or rubber), safety glasses, and an N95 mask for heavy growth
• Stiff nylon brush or old toothbrush; grout brush
• Detergent, a bathroom cleaner labeled for mold and mildew, or a baking soda paste
• Microfiber cloths
• For caulk replacement: utility knife or caulk removal tool, rubbing alcohol, painter’s tape, and a tube of 100% silicone mold-resistant bathroom caulk

Step 1: Ventilate and protect yourself

Turn on the exhaust fan and open a window if there is one. Put on gloves and eye protection. If someone in the home has asthma, let someone else do the cleaning.

Step 2: Clean the grout

1. Spray the grout with your cleaner (or apply a paste of baking soda and water) and let it sit for the time on the label — usually 5–10 minutes.
2. Scrub along the grout lines with a stiff brush.
3. Rinse thoroughly and dry with a towel.
4. For stubborn stains on plain cement grout, an oxygen-bleach (sodium percarbonate) paste can lift discoloration. Rinse well.

Step 3: Decide whether to clean or replace the caulk

Wipe the caulk with your cleaner and scrub gently. Then look closely:

• Spots gone? Great — it was surface growth. Dry the area and move to prevention.
• Spots still visible beneath a clean surface? The mold has grown into or behind the silicone. No cleaner will reach it. Replace the caulk.

Step 4: Replace moldy caulk

1. Cut out the old caulk along both edges with a utility knife or caulk tool, then pull it away.
2. Remove residue with the tool and a scrub pad.
3. Clean the joint with detergent, rinse, then wipe with rubbing alcohol to remove soap film.
4. Let it dry completely — ideally 24 hours with the fan running. Caulking over a damp joint traps moisture and mold.
5. Tape both sides of the joint with painter’s tape for a clean line.
6. Apply a continuous bead of mold-resistant 100% silicone, smooth it with a wet finger or tool, and remove the tape immediately.
7. Wait for the cure time on the tube (often 24 hours) before showering.

Step 5: Stop the mold from coming back

Cleaning removes mold; drying the room prevents it.

• Run the exhaust fan during every shower and for 20–30 minutes after. If your fan is weak or noisy, replacing it is one of the best upgrades you can make. A humidity-sensing fan switch turns it on automatically.
• Squeegee walls and glass after showering.
• Leave the door and shower curtain open to dry.
• Wash fabric shower curtains and bath mats regularly.
• Seal grout once a year with a penetrating grout sealer.
• Keep whole-home humidity at 30–50% — see Ideal Indoor Humidity.

When it’s more than surface mold

Call a professional or investigate further if:

• mold returns within weeks despite good ventilation;
• tiles are loose, grout is crumbling, or walls feel soft — water may be getting behind the tile;
• you see mold on the ceiling, walls outside the shower, or around the toilet base;
• there’s a musty smell from the wall cavity.

These can mean a leak or failed waterproofing. Our guide to hidden mold in walls explains how to check, and the mold hub guide covers when remediation is needed.

Health note: This article is for general information and isn’t medical advice. If you or someone in your home has symptoms such as wheezing, a persistent cough, a rash that spreads, or a fever after a bite, talk to a doctor or other qualified health professional. Read our disclaimer.