What Is the Pink Mold in My Shower?
It is usually bacteria. The Notla Water Authority in Georgia says the pink substance people see in toilet bowls, shower stalls, bathtub enclosures, on tiles and in sinks is most commonly caused by a red or pink pigmented bacterium called Serratia marcescens, which grows in moist places where phosphorus containing materials or fatty substances accumulate, such as soap residue in bathing areas.
Studies point to other bacteria too. A peer-reviewed survey of 42 pink biofilms in bathrooms in Japan found they develop relatively rapidly, can be difficult to remove and are quick to recur, and identified Methylobacterium as the major genus in all the biofilms analyzed. A second study concluded that Methylobacterium is one of the dominant bacteria in the pink slime that widely forms in bathrooms.
The water authority says Serratia marcescens is not known to cause any waterborne diseases, though it has been identified as a cause of urinary tract infections, wound infections and pneumonia in a small percentage of people in hospital environments. A 2020 paper describes Methylobacterium species as emerging opportunistic premise plumbing pathogens. The water authority says the organism usually cannot be eliminated entirely once established, but that periodic, thorough cleaning followed by disinfection with chlorine bleach appears to be the best way to control it.
Sources checked September 15, 2026. Every point below links the page it came from.
The sources behind this answer
- Government sourceThe Notla Water Authority says pink slime in toilets, showers, tubs and sinks is most commonly caused by a red or pink pigmented bacterium called Serratia marcescens. Notla Water Authority, Georgia ↗
- Government sourceThe Notla Water Authority says the bacteria grow in moist places where phosphorus containing materials or fatty substances accumulate, such as soap residue in bathing areas. Notla Water Authority, Georgia ↗
- Government sourceThe Notla Water Authority says Serratia marcescens is not known to cause waterborne diseases, but has caused urinary tract and wound infections and pneumonia in hospital settings. Notla Water Authority, Georgia ↗
- Government sourceThe Notla Water Authority says the organism usually cannot be eliminated once established, but periodic thorough cleaning followed by chlorine bleach disinfection appears to control it best. Notla Water Authority, Georgia ↗
- StudyA survey of 42 pink bathroom biofilms in Japan found they develop rapidly, are hard to remove and recur, and identified Methylobacterium as the major genus in all biofilms analyzed. Microbes and Environments, via PubMed Central ↗
- StudyA study of pink slime from household bathrooms concluded that Methylobacterium is one of the dominant bacteria in the pink-pigmented slime that widely forms in bathrooms. Microbes and Environments, via PubMed Central ↗
- StudyA 2020 paper describes Methylobacterium species as emerging opportunistic premise plumbing pathogens. Pathogens, via PubMed Central ↗
Sources checked September 15, 2026. A brand statement is the company’s own claim, which we report but have not verified. Our grades are model-based estimates, not lab tests.