Pink mold in the shower is not mold: what it is and how to clean it

What is pink mold in the shower?

The pink, salmon or orange film that shows up on shower grout, caulk, drains, curtains and toilet bowls is almost always not mold. North Dakota State University (NDSU) Extension identifies it as Serratia marcescens, a bacterium. Water utilities in Winston-Salem, North Carolina, and Dubuque, Iowa, say the same in their customer guidance. The color is a pigment the bacteria produce.

Mold is a fungus. It grows as branching filaments and often looks fuzzy, velvety or spotty. Serratia forms a slimy, wet film instead. It wipes off fairly easily but comes back quickly in the same damp spots.

The confusion is understandable. An extension specialist answering a homeowner on Ask Extension put it this way: the pink or orange discoloration is not mold, but it grows under the same conditions mold favors, so the two get mixed up. The good news is that the steps that control Serratia also help keep bathroom mold down. For true mold in bathrooms, see our bathroom mold guide, and for all mold topics, start at our mold hub.

Where does pink slime come from?

Serratia lives in the environment. Winston-Salem/Forsyth County Utilities says it commonly inhabits soil, dust, mulch and surface water, and travels through the air. Once airborne, the bacteria settle on moist surfaces and grow if conditions are right.

It does not come through properly treated tap water. The Winston-Salem utility says the bacterium may be present in source water but does not survive the treatment process, and does not enter homes through its system. The bacteria grow in your bathroom, not in the pipes.

Three conditions let it grow, according to the utility and NDSU Extension:

• Standing water. Water that sits long enough loses its residual chlorine. This is why the pink ring often appears in guest toilets or after a trip.
• Food. Soap, shampoo and detergent residue (which contain phosphorus), fatty residues, urine and feces, and food scraps in pet bowls all feed it.
• Warmth and humidity. Utilities report more complaints in summer, especially when windows are open. NDSU Extension and the Winston-Salem utility also note it often appears during or after construction or remodeling.

NDSU Extension adds that activated carbon water filters, which remove chlorine, may help the bacteria grow.

How can you tell pink slime from mold?

Look at the texture, the location and how it behaves when you clean it. The table compares what the sources describe.

If you see dark or fuzzy spots on drywall or the ceiling, that is a different problem. See our guides to mold vs mildew and black mold.

Is pink slime harmful?

For most healthy people, it is a cleaning problem rather than a health emergency. NDSU Extension says the genus Serratia is not known to be a waterborne disease. It also notes that Serratia has been known to cause pneumonia, wound infections and urinary tract infections in some hospital settings.

Winston-Salem/Forsyth County Utilities says Serratia marcescens has been found to cause illness in people whose immune systems are weakened by disease or medical treatment. It advises anyone with concerns about their own health to talk with a physician.

That is a reasonable line to draw at home. If everyone in the household is healthy, clean the film regularly and do not worry beyond that. If someone has a weakened immune system, for example from a medical condition or treatment, clean pink slime promptly and ask their care team whether other precautions make sense.

CDC’s mold guidance does not cover Serratia, because it is not a mold. None of the sources reviewed for this page describe any test you need to run on it.

How do you clean pink slime?

NDSU Extension and the Winston-Salem utility give similar steps:

1. Scrub the film off with a brush and a general household cleaner. Avoid harsh abrasives on fixtures; the utilities note scratches create more places for bacteria to grow.
2. Disinfect with a chlorine bleach product, following the label. NDSU Extension suggests leaving the disinfectant on for 10 to 20 minutes, then rinsing well with water.
3. Toilet tank: NDSU Extension suggests adding 1/4 cup of bleach to the tank, letting it sit 15 to 20 minutes, then flushing a few times. Do not leave bleach in the tank; it can damage rubber valves and seals.
4. Curtain liners: wash or replace a slimy liner. The Ask Extension specialist notes water trapped in liner folds helps the film return.

CDC’s rule for any bleach use applies here: never mix bleach with ammonia or other cleaners, because it produces a poisonous gas. Open a window or run the fan.

If you prefer to avoid bleach, an extension specialist on Ask Extension suggested a half-water, half-vinegar spray left on for 10 minutes, then scrubbed and rinsed. Do not use vinegar and bleach together. Our guide to what actually kills mold compares common cleaners for true mold.

How do you keep pink slime from coming back?

Utilities say that once established, Serratia usually cannot be eliminated entirely, because it keeps arriving from household air and dust. The goal is to stop giving it standing water and food.

NDSU Extension recommends wiping down and drying sinks and tubs after use. The Ask Extension specialist suggested three habits for showers:

• Run the bathroom fan during and after every shower. It may take up to 60 minutes to clear the moisture.
• Squeegee the shower walls after use, which removes both water and soap residue.
• Pull the shower curtain fully closed after showering so water does not sit in the folds.

The utilities add periodic, thorough cleaning followed by disinfection, and scrubbing pet water bowls rather than just refilling them. Because NDSU Extension links the toilet ring to water that sits for days, flushing seldom-used toilets regularly is a sensible habit.

These same steps help with true mold. EPA’s guidance for bathrooms says that if mold keeps reappearing in the shower, increasing ventilation by running a fan or opening a window, and cleaning more often, will usually prevent it or keep it to a minimum. If your fan does not vent outside, or does not clear steam, that is worth fixing. See our mold prevention guide for humidity targets.

What about orange or red growth?

Orange and red films in bathrooms are usually the same Serratia bacteria at a different stage or concentration. NDSU Extension describes it as a “pinkish-red substance,” and an Ask Extension specialist described a pink-orange discoloration as most likely Serratia. Clean them the same way.

True mold can also come in many colors, according to CDC. If an orange or red growth is fuzzy, has a musty smell, or sits on drywall, ceiling paint or wood rather than tile and porcelain, treat it as mold. EPA says a moldy odor suggests mold is growing and should be investigated.

The location tells you the most. Slime at the water line, on the drain or along the tub edge is almost always bacterial film. Growth on walls or ceilings means moisture is reaching building materials, which EPA says should be dried within 24 to 48 hours. If it covers more than about 10 square feet, EPA suggests professional help; see our guide to choosing a mold remediation company.