How to Remove Mold from Shower Caulk (and Stop It Coming Back)

Black spots on the caulk around your shower or tub are very common. Caulk stays damp, soap scum feeds mold, and the soft surface makes it easy for spores to settle in. Sometimes the spots come right off. Other times, the mold is growing underneath the caulk, and the only real fix is replacing it. Here's how to tell, and what to do.

What You'll Need

Rubber gloves and eye protection
Chlorine bleach or 3% hydrogen peroxide
Cotton balls, cotton coil or paper towels
Plastic wrap (optional)
An old toothbrush
A fan or open window for ventilation

Safety First

Open a window and turn on the bathroom fan.
Never mix bleach with vinegar, ammonia or any other cleaner. Rinse surfaces well before switching products.
Wear gloves and avoid getting bleach on towels, rugs or clothes.

Step 1: Clean the Surface

Wash the caulk with warm soapy water and a toothbrush to remove soap scum and loose mildew. Rinse and dry. This lets the treatment reach the mold directly.

Step 2: Apply the Treatment

Bleach method (most effective on white caulk):

Soak cotton coil, cotton balls or rolled paper towels in a solution of 1 part bleach to 2 parts water.
Press them along the moldy caulk so they stay in direct contact.
Cover with plastic wrap to keep them from drying out (optional).

Hydrogen peroxide method (no bleach):

Soak the cotton in 3% hydrogen peroxide instead, and apply it the same way. Peroxide is gentler and has no strong smell, but may need repeating.

Step 3: Let It Sit

Leave it for several hours or overnight. Keep the room ventilated during this time.

Step 4: Remove and Rinse

Wearing gloves, remove the cotton and throw it away. Scrub the caulk gently with the toothbrush, rinse thoroughly with water, and dry the area.

Still See Black Spots?

If the black marks are still there after one or two treatments, the mold is likely under or inside the caulk. Surface cleaning can't reach it. In that case, the best fix is to:

Cut out the old caulk with a utility knife or caulk removal tool.
Clean and disinfect the joint underneath, then let it dry completely, ideally for 24 hours.
Apply a new bead of mold-resistant silicone caulk made for kitchens and baths.
Let it cure fully (check the label, often 24 hours) before using the shower.

How to Stop Mold from Coming Back

Run the exhaust fan during and for at least 20–30 minutes after showers.
Squeegee walls and wipe the caulk lines after each shower.
Keep the shower door or curtain open after use so it can dry.
Clean the shower weekly to prevent soap scum buildup.
Fix leaks and drips promptly.

When to Call a Professional

If mold covers a large area (the EPA suggests about 10 square feet or more), keeps coming back quickly, or appears on walls and ceilings outside the shower, it may be a sign of a moisture problem behind the surface. A professional can check for leaks and safely handle larger mold problems.

FAQ

Is black mold on shower caulk dangerous? Mold can trigger allergies and breathing irritation in some people. It's best to remove it promptly and keep the bathroom dry.

Does vinegar kill mold on caulk? Vinegar can help with light surface mildew, but it's generally less effective on stubborn black spots in caulk than bleach or peroxide.

How often should I replace shower caulk? Every few years, or whenever it cracks, peels or stays stained after cleaning.