It isn't every household mold that has inspired a Catholic feast day and has its portrait displayed in the Vatican, but pink mold isn't your everyday mold. In fact, the microorganism that grows to become pink mold, Serratia marcescens, isn't actually mold at all. Mold is a type of fungus, and S. marcescens is a bacterium, and it shows up in your bathroom because it likes soap, moisture, and other things you find in bathrooms. When given time to mature, certain strains of S. marcescens may take on a deep red coloration, but on bathroom walls and inside toilets, it may form a thin film that appears pink and turns orange and finally red as the film gets thicker.
Like many microorganisms, S. marcescens grows readily in damp bread, and its red pigment, called prodigiosin, is close enough to that of blood that many microbiologists believe it was responsible for an apparent miraculous transubstantiation that occurred as a priest celebrated Mass in the Church of Saint Christina in Bolsena, Italy, in 1263. The Eucharist bread suddenly turned red and began dripping onto the altar. This event prompted Pope Urban to institute the Feast of Corpus Christi, and almost 300 years later, renaissance painter Raphael depicted the event in a fresco on the wall of the Apostolic Palace in Vatican City. It's still there.
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Of course, when you see this "miraculous" substance growing on your bathroom walls, your first thought is probably how to clean it and prevent it from coming back. You might also be wondering if it's as dangerous for your health as some other bathroom pathogens, like toxic black mold. The good news is that it isn't, but despite what people used to think, it isn't entirely benign either.
What Is Pink Mold, and How Toxic Is It?
Pink mold does have the ability to cause urinary tract infections, stomach ailments, and pneumonia, but healthy individuals usually have enough natural immunity to resist them. However, these infections can lead to disease in people with a compromised immune system as well as elderly, very young, or malnourished individuals. Pink mold can also cause infections in open wounds, and if you touch it with your bare hands and then touch your eyes, it can cause eye infections. In other words, it's toxic enough to be a cause for concern when you see it in your bathroom, and you should clean it immediately.
Because of its red pigment, researchers use S. marcescens as a tracer organism in medical and dental experiments, and it was also used by the military. In the 1950s, the U.S. government conducted a test in San Francisco called Operation Sea Spray to determine how vulnerable the population was to a biological attack. It released large quantities into the atmosphere to measure how long they took to disperse, and as revealed in later government hearings, 11 people developed serious urinary tract infections, and one died. The Army maintained that the illnesses were unrelated to the test, however, and courts agreed.
Why Does Pink Mold Grow in the Shower?
The bathroom, particularly the shower, has everything pink mold needs to thrive, including warm temperatures, lots of moisture, and food. The bacteria feast on the soap scum that collects on shower walls, the shower curtain, the showerhead, and faucets in the shower and elsewhere in the bathroom. They also feed on greases and oils that collect in tile grout and on fecal matter in the toilet bowl.
Because of the excess moisture there, the shower is usually ground zero for pink mold growth but not always. A colony may grow in the toilet, when the chlorine in treated municipal water evaporates, and when there's enough moisture in the bathroom, it can spread to other places, like the sink and shower. Airborne bacteria usually get into the bathroom from outdoors, and because they are virtually everywhere, it's difficult to prevent a pink mold infestation.
How to Clean Pink Mold
Bleach is a powerful disinfectant that kills bacteria and mold, but before you reach for that spray bottle, keep in mind that bleach has a high surface tension that prevents it from penetrating grout, wood, and other porous materials. Simply spraying tiles with chlorine bleach leaves the bacteria in the grout undisturbed, and the colony will grow back. Besides that, bleach is corrosive and damages grout over time, and it can also cause health problems. (You should also always wear personal safety gear like gloves, goggles and a respirator when using it.)
The Centers for Disease Control and Prevention recommends ethyl alcohol as an alternative to bleach for disinfecting S. marcescens:. Concentrations from 30 to 100 percent have been shown to effectively kill the bacterium when in contact for at least 10 seconds. (Most store-bought ethyl rubbing alcohol has a concentration of 70 percent.) There are two ways you can use it:
- Spray the mold with full-strength rubbing alcohol, let the alcohol sit for at least 10 seconds, then wipe it away.
- Or, dampen a sponge, rag or cotton swab with rubbing alcohol and rub for 10 seconds or more.
You can scrub pink mold from shower curtains and curtain liners using this method, but it's usually easier — and you're more likely to get all the mold off — if you put them in the washing machine. Be sure to dry them completely before rehanging them.
How to Keep Pink Mold Away
S. marcescens may not actually be mold, but it's still alive, and like any type of microorganism, it needs moisture and a food source. If you keep your shower clean and dry, your chances of keeping pink stains away are better than if you don't. Keeping a shower dry is a tall order since people go there to get wet, so you have to be extra diligent. Here are a few tips for keeping pink mold away:
- Turn on the exhaust fan while you shower and leave it on for a few minutes afterward.
- Use a squeegee to wipe down the shower walls after every shower and keep the shower curtain or door open to allow air to circulate when the shower isn't in use.
- As part of your bathroom cleaning routine, spray some of the disinfectant you used to clean the shower in corners and dark places where condensation collects. Spray some in the toilet bowl and behind the toilet, as these are favorite places for pink mold colonies to grow. If you want, you can use bleach for this, even on porous surfaces, because it will kill bacteria on the bathroom surfaces you spray and prevent a buildup.
Orange Stains Might Not Be Pink Mold
A mature colony of S. marcescens appears deep red, but the film on a bathroom wall is usually only thick enough to appear pink or possibly orange. However, that doesn't mean every orange deposit in the shower is S. marcescens. Some of the minerals in hard water, especially iron, can leave orange or brownish-orange residue on the shower walls and floor and on faucets and other fixtures. These deposits are qualitatively different from pink mold and are usually more difficult for homeowners to remove.
Mineral deposits may look horrendous, but they don't present a health problem. They aren't alive, so you can't kill them with a disinfectant as you can mold and mildew. Here's how to remove orange mineral deposits:
- Treat the area for mold first. Because pink mold and minerals can build up in the same places, it's usually more efficient to treat the area for mold first (because it's easier to remove) and then scrub away any discoloration that remains.
- Mix full-strength vinegar or lemon juice with borax or laundry detergent. Baking soda might also work, and it's what many cleaners recommend, but it reacts with acids, like vinegar and lemon juice, and neutralizes them, so you'll be losing cleaning power.
- Spread the paste on the stains, come back in an hour, scrub the stains away with a soft-bristle scrub brush, and rinse with clean water.
- If the stains don't come out the first time, try again, but this time, spray the paste once or twice with extra vinegar or lemon juice to prevent it from drying out.
Vinegar and other acidic cleaners can damage natural stone tile and, over time, cement-based tile grout. Avoid acidic cleaners on stone tile. For grout, vinegar is ok to use one in a while for stain removal, but it shouldn't be used for regular everyday cleaning.