Clean Mildew from Shower Caulk

Mildew grows on shower caulk because the joint between your tile and tub offers everything a fungus needs: moisture, warmth, and organic residue from soap and skin cells. That black or orange staining along the caulk line isn't dirt you can wipe away. It's a colony that's rooted into the silicone itself, and surface cleaning won't touch it. The good news is that most caulk mildew lives in the top layer of sealant and responds to chemical treatment without requiring full removal and re-caulking. The difference between a shower that looks maintained and one that looks neglected often comes down to those caulk lines. Clean caulk reads as clean bathroom. Stained caulk makes everything else look questionable, even if your tile is spotless. This is a thirty-minute job that pays back in perception every single day.

1. Dry Before You Treat. Wipe down all caulk lines with a dry towel and let the shower air out for two hours with the door open and exhaust fan running. Mildew treatment works best on dry surfaces because water dilutes your cleaning solution and prevents it from penetrating the silicone. If you're in a hurry, use a hair dryer on low heat to speed the drying.
2. Spray and Saturate. Mix one part household bleach with three parts water in a spray bottle. Spray directly onto the mildewed caulk until it's thoroughly wet, then let it sit for fifteen minutes. For stubborn stains, lay bleach-soaked paper towels directly on the caulk line to keep the solution in contact longer. Work with the bathroom door open and exhaust fan on.
3. Brush Out the Stain. Use an old toothbrush or dedicated grout brush to scrub along the caulk line in short, firm strokes. Focus on the edges where the caulk meets the tile or tub, where mildew digs in deepest. You're not trying to remove the caulk itself, just the top layer where the staining lives. Re-spray with bleach solution as needed to keep the area wet while you work.
4. Flush All Residue. Run hot water over all treated areas for at least two minutes, making sure no bleach residue remains. Use your hand to feel along the caulk line — if it's slippery, there's still cleaner present. Residual bleach will continue breaking down the silicone after you're done, which weakens the seal over time.
5. Go Deeper If Needed. For stains that survived bleach treatment, spray undiluted 3% hydrogen peroxide directly on the spot and let it sit for thirty minutes. Hydrogen peroxide works more slowly than bleach but penetrates deeper into silicone without the harsh fumes. This is particularly effective on orange or pink mildew that resists chlorine bleach.
6. Inspect for Damage. Wipe down the caulk with a clean towel and run the exhaust fan for an hour. Check the caulk lines in bright light — look for any lifting, cracking, or gaps that might have been hidden under the mildew. If the caulk itself is damaged or if black staining remains after two rounds of treatment, the mildew has penetrated too deep and the caulk needs replacement.
7. Lock in Your Win. Spray the cleaned caulk with a light mist of white vinegar and let it air dry — the acidic environment discourages new mildew growth. Going forward, squeegee the shower walls after every use and run the exhaust fan for twenty minutes post-shower. Monthly quick-cleaning with hydrogen peroxide keeps mildew from re-establishing.