My shower curtain started going pink along the bottom. I assumed it was rust from the water, or dye running out of the fabric.
It is neither. It is alive.
What the Pink Actually Is
It is a bacterium called Serratia marcescens. It is not mold and it is not mildew, which is why mold sprays often do very little to it.
It is airborne and it is everywhere — in soil, in dust, outdoors. It cannot do anything until it lands somewhere permanently wet with something to eat.
A shower curtain is exactly that. What it eats is the fatty residue from soap and shampoo, and the pink-orange color is a pigment the bacteria produce.
This is also why it appears around drains, in pet water bowls, in toilet bowls, and in the seal of a front-loading washing machine. Same organism, same conditions.
How to Get Rid of It
A plastic or vinyl curtain goes in the washing machine. Warm wash with your normal detergent and a cup of white vinegar, plus a couple of towels in with it so there is something to scrub against. Hang it straight back up damp so it does not crease.
For a fabric curtain, wash hot if the label allows it, with detergent and half a cup of baking soda.
For the tiles and the tub, a spray of one part bleach to ten parts water, left ten minutes, then rinsed well. Bleach does kill it — it just cannot reach it through the soap film, so clean the surface first.
Do not mix bleach with vinegar or with any other cleaner. It makes chlorine gas.
Why It Comes Back
Because you removed the bacteria and left the two things it needs: moisture and soap scum.
It is in the air and it will land there again within days. The only way to keep it away is to make the surface a place it cannot live.
How to Stop It Coming Back
Spread the curtain out fully after every shower. Bunched up it stays wet for hours. Spread flat it dries in twenty minutes and nothing can grow.
Run the fan or open the window for fifteen minutes after showering. This matters more than anything else you can do.
Switch from bar soap to a liquid body wash. Bar soap leaves far more of the fatty residue the bacteria feed on. People who make this one change often never see pink again.
Rinse the bottom of the curtain and the tub with hot water after a shower. Ten seconds.
Wash the curtain monthly rather than waiting for it to turn.
Should You Worry About It?
For a healthy person in a bathroom, no. It is treated as a nuisance, not a hazard.
It is worth taking seriously in a humidifier, a CPAP machine or a pet’s water bowl, where you are breathing it in or drinking from it. Those get cleaned properly and often.
