Open a window or run the fan, and wear gloves. Never mix bleach with ammonia, vinegar, or other cleaners.
What you'll need
You probably have these
Tick them off as you find them.
Only if you're missing something
- 100% silicone kitchen and bath caulkMildew-resistant is worth it$7 to $12
- Bathroom mildew cleanerUse one product only$4 to $8
- Caulk gunOnly if you don't have one$5 to $10
Links go to Amazon. Prices shown are estimates. As an Amazon Associate we earn from qualifying purchases. How we make money
The fix
- 1
Air out the room
Turn on the fan or open a window. Put on rubber gloves.
You'll know it's right whenAir is moving through the bathroom.
- 2
Scrub the grout
Spray a bathroom mildew cleaner on the grout and follow the label. Scrub with a stiff brush.
You'll know it's right whenThe grout lines get lighter as you go.
- 3
Rinse and dry
Rinse with water. Wipe the tile dry with a towel.
You'll know it's right whenClean grout, no black specks.
- 4
Cut out stained caulk
If the caulk still has black spots, slice along both edges with a utility knife. Peel it out.
You'll know it's right whenThe old caulk comes away in strips. Looks worse for a minute. Normal.
- 5
Clean the joint
Scrape off leftover bits. Wipe the gap with rubbing alcohol and let it dry fully, ideally overnight.
You'll know it's right whenThe gap is bare, clean, and dry.
- 6
Run a new bead
Use 100% silicone caulk labeled for kitchen and bath. Squeeze a steady bead along the gap.
You'll know it's right whenThe bead touches both sides with no gaps.
- 7
Smooth it and wait
Smooth the bead with a wet fingertip or a caulk tool. Let it cure as long as the label says, often 24 hours.
You'll know it's right whenA clean, even line that's dry to the touch.
Bright white lines. Your shower looks new again!
Why it happens
Showers stay warm and wet for hours, which is exactly what mold loves. Grout is porous, so mold can sit in its tiny holes. Caulk is softer, so mold grows down into it where scrubbing can't reach. That's why the spots keep coming back no matter how hard you clean.
Edie's tipRun the bathroom fan during your shower and for 20 to 30 minutes after.
What not to do
- Caulking over old caulk
New caulk won't stick well and the mold underneath shows through.
- Mixing cleaners
Bleach plus ammonia or vinegar makes toxic gas. Use one product at a time and rinse between.
- Showering too soon
Water on uncured silicone can ruin the seal. Wait as long as the label says.
- Using acrylic caulk
100% silicone holds up to water and mildew far better in a shower.
When to call a pro
Call a pro if tiles are loose or the wall behind the tile feels soft. Call too if mold shows up outside the shower, or it comes back fast after recaulking. That can mean water is getting behind the tile.
Questions
Is shower mold the dangerous black mold?
Most black spots in showers are common surface mildew. Clean it, dry it, and keep air moving. Color alone doesn't tell you the type.
Can I clean the caulk instead of replacing it?
You can try. If black spots remain after a good scrub, the mold is inside the caulk and it has to come out.
Should I seal the grout?
A grout sealer after cleaning helps it resist stains. Follow the label for how long to wait before showers.
Written by the DIY Project team and checked against manufacturer instructions. How we check
Updated October 2, 2026.
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