How to Remove Mildew from Bathroom Caulk

Mildew in bathroom caulk is one of those problems that looks worse than it actually is to fix. The dark spots and fuzzy growth appear almost overnight in that strip of caulk around your tub or shower, thriving in the moisture and poor ventilation that bathrooms naturally provide. The good news: most mildew removal takes under an hour and costs almost nothing. The bad news: if the caulk is degraded, crumbling, or the mildew keeps coming back within a week, you're looking at replacement instead of cleaning. This guide covers both paths—cleaning when it'll work, and knowing when to pull it out and start fresh.

1. Clear the area and improve ventilation. Remove any items from the tub, shower, or sink area. Open windows and turn on the bathroom exhaust fan to maximum. If you have a space heater, position it to help dry the area—moisture is mildew's best friend. Let the fan run for at least 10 minutes before you start.
2. Choose your cleaning agent. For surface-level mildew, white vinegar works well and is safest. For heavy or stubborn growth, dilute household bleach at a 1:1 ratio with water in a spray bottle. Never mix bleach with ammonia or other cleaners. If the caulk is already crumbling or has deep staining, skip ahead to replacement.
3. Apply the cleaning solution generously. Spray your chosen cleaner directly onto the moldy caulk, coating it completely. Don't be stingy—the solution needs to penetrate the caulk and reach mold spores below the surface. Spray again if the first coat dries quickly.
4. Let the cleaner sit and work. Leave the solution on the caulk for 10-15 minutes if using vinegar, or 5-10 minutes if using bleach. Set a timer. The longer you wait, the more time the cleaner has to break down the mildew structure and kill spores deeper in the caulk. Don't let bleach sit much longer than 10 minutes, as it can damage some caulk materials.
5. Scrub with a stiff brush. Use an old toothbrush, grout brush, or a small handheld scrub brush with stiff bristles. Apply firm pressure and scrub back and forth along the entire length of the caulk line. You'll see the mildew loosen and break up. Work methodically—this is where the actual removal happens.
6. Rinse and dry completely. Use clean water and a sponge or cloth to rinse away all cleaning solution and loosened mildew debris. Rinse twice if using bleach to ensure no chemical residue remains. Then dry the caulk thoroughly with a clean cloth or paper towel. This is critical—any remaining moisture will encourage mildew to return.
7. Inspect and decide on replacement. Look at the caulk closely. If it's still discolored after cleaning, crumbling at the edges, pulling away from the surface, or if mildew reappears within a week, replacement is your next move. Use a caulk removal tool or a utility knife to cut out the old caulk, clean the joint with a damp cloth, let it dry completely, and apply fresh paintable or waterproof caulk.