Black Mold in the Shower: How to Remove It and When It Signals a Bigger Problem

Black spots on shower grout, caulk, and tile are one of the most common mold problems in any home. In most cases, they are surface mold, often called mildew, feeding on soap residue and daily moisture, not the Stachybotrys that people usually mean by "black mold." They are usually easy to clean. The time to worry is when the mold keeps coming back or shows up outside the shower, because that can mean water is getting behind the tile.

This guide covers how to remove shower mold, how to keep it from returning, and the signs that it is a symptom of a leak.

Why showers grow mold

A shower gives mold everything it needs:

• Moisture every day, often more than once
• Food from soap scum, shampoo residue, and skin oils
• Slow drying in corners, along the tub edge, and behind bottles
• Porous surfaces such as unsealed grout and aging caulk that hold water
• Weak ventilation when the exhaust fan is missing, undersized, or not used

That is why the same corners turn black again and again.

How to remove black mold from a shower

For tile, grout, glass, and the tub surface:

1. Protect yourself. Open a window or run the fan, and wear gloves and eye protection. If you have asthma or a mold allergy, have someone else do it.
2. Scrub with detergent and water. Use a stiff brush on grout lines and corners. The EPA's basic guidance for hard surfaces is to scrub mold off with detergent and water and dry completely.
3. Rinse and dry. Wipe everything down and leave the door or curtain open so the space dries.
4. Deal with caulk that stays black. If the stain remains after cleaning, the mold is inside the caulk. Cut the old caulk out, clean the joint, let it dry fully, and apply new caulk made for bathrooms.
5. Seal the grout. Once the grout is clean and dry, a grout sealer slows how fast it absorbs water. Grout that stays stained or crumbles may need to be replaced.
6. Wash or replace the curtain and liner. They grow mold too.

The EPA does not recommend bleach or other biocides as a routine part of mold cleanup. If you use any cleaning product, follow the label, ventilate the room, and never mix bleach with ammonia or other cleaners, because the fumes can be toxic.

Keeping it from coming back

• Run the exhaust fan during every shower and for a while afterward, until the mirror clears
• Squeegee or wipe down walls and glass after showering
• Leave the shower door or curtain open to let it dry
• Store bottles on a rack rather than on the tub edge
• Fix dripping shower heads and faucets
• Clean the shower every week or two, before spots take hold
• Keep indoor humidity below 60 percent, as the EPA recommends

If the bathroom has no exhaust fan, or the fan does not pull air (a tissue held against the grille should stay put), that is often the root cause.

Black mold elsewhere in the bathroom

Around the tub. The caulk joint between the tub and the wall is a common spot. Treat it like shower caulk: if cleaning does not remove the stain, replace the caulk.

Toilets. A dark ring at the waterline can be mold or mineral deposits. Regular cleaning handles either. Mold, staining, or a soft floor around the base of the toilet is different: it can mean the seal under the toilet is leaking.

Ceilings. Dark spots on a painted bathroom ceiling usually come from steam and poor ventilation. Small areas can be cleaned and dried. If spots return quickly or the ceiling is stained or sagging, check for a leak from above, such as a roof, another bathroom, or an air conditioning line.

Under the sink. Mold in the vanity cabinet almost always means a slow drip from a supply line, faucet, or drain.

When shower mold means a leak

Surface mold stays on the surface. Be suspicious of a hidden leak if you notice:

• Loose, cracked, or hollow-sounding tiles
• Grout that crumbles or keeps cracking
• A wall around the shower that feels soft or bulges
• Stains, bubbling paint, or mold on the ceiling below the bathroom
• Peeling paint or mold on the other side of the shower wall
• A musty smell outside the bathroom
• Mold that returns within days of a thorough cleaning

These can come from a failing shower pan, a leaking valve or pipe inside the wall, or water getting through grout and tile into the drywall behind. The EPA notes that mold often grows on hidden surfaces such as the back side of drywall. At that point, cleaning the tile will not fix it. The wall usually has to be opened by someone who can contain the area and find the leak. See mold behind drywall and what a mold inspection involves.

Is shower mold dangerous?

Molds, including the kinds that grow in showers, produce allergens and irritants, so they can trigger symptoms in people with allergies or asthma. For most people, a few spots on grout are a cleaning chore rather than a health emergency. If anyone in the home is sensitive to mold, keep the shower clean and let someone else do the scrubbing. See is black mold dangerous? and mold vs. mildew.

What it costs

Cleaning and recaulking a shower yourself costs little beyond a brush, detergent, and a tube of caulk. When mold has spread into the wall or subfloor, professional bathroom mold remediation typically runs about $500 to $2,000, according to HomeGuide, plus the cost of fixing the leak and replacing tile or drywall. See our mold remediation cost guide.

Bathrooms in Florida

Florida's humidity means bathrooms dry slowly, especially in homes where the air conditioning is set high or turned off while owners are away. In condos, a leaking shower pan or valve can show up as mold in the unit below. See local pages for Miami, Boca Raton, and the rest of Florida.

Next step

If the mold in your bathroom keeps coming back, has spread beyond the shower, or you see signs of a leak behind the tile, and you own the home, call the number on this page to be connected with an independent local mold removal company.