Black mould showing up in a bathroom usually signals a proper clean is in order.
But have you ever noticed a pink or orange-coloured substance in the tile grout or around taps?
In most cases, it's one of two things, explains Michael Taylor, an expert in mould and adjunct academic with Flinders University.
We look at what those are, how to deal with them, and whether they can make you sick.
When it's mould
The pink slime may be a type of micro fungi, also called a mould, named Rhodotorula, explains Dr Taylor.
"It's more like a yeast. It makes a slimy coating around itself and will happily live in wet environments."
He says Rhodotorula can be found almost anywhere, including on and in the wet bits of your skin.
While Rhodotorula poses no risk to healthy people, Dr Taylor says it can cause infection in those with weakened immune systems.
When it's bacteria
The more likely cause of the pink scum in your bathroom is a bacteria called Serratia marcescens, says Dr Taylor.
It's another microbe that thrives in damp and humid conditions.
"It also makes a slimy, mucus coating — a biofilm — which is what lets it persist in these environments.
"It also lets it soak up nutrients to live … these sticky coatings let them sort of grab little bits of food as they float by and use those to grow."
Dr Taylor says the bacteria belongs to a group of pathogens known as "opportunists".
"If conditions are right, say [a] person exposed is immunocompromised … [the bacteria] may find a cut or something like that they can get into, and slowly do their thing."
That may be causing a mild infection that could turn into something more serious, like pneumonia, and require treatment, explains Dr Taylor.
But most people are generally not at risk of Serratia infections.
Jane Whitelaw, a certified occupational hygienist at the University of Wollongong, says for most of us it's just a "background level of exposure" that we are subject to day-to-day.
"It doesn't really do us any harm."
And it's hard to say exactly how "risky" the bacteria is, because how it impacts someone depends on their immune system.
"It's really individual whether or not you will be susceptible and how serious it is likely to be."
How to clean pink soap scum
Dr Taylor says it's a misconception to think you can ever make your bathroom completely sterile, but there are ways to reduce the presence of mould and bacteria.
Recommendations from Dr Taylor and Ms Whitlaw include:
- Drying wet areas to reduce the moisture that helps mould and bacteria grow.
- When cleaning the area, remove the bulk of the scum before using disinfectant. "You need to clean first, disinfect second," Dr Taylor says. You can wipe or scrub the area before adding a product such as bleach, or mix of vinegar and water. "Vinegar is a really good cleaning agent," says Ms Whitelaw.
- Wear disposable gloves and throw them out after cleaning the area so you don't spread the mould or bacteria.
Ms Whitelaw says the pink soap scum returning doesn't necessarily mean you haven't cleaned it property.
"It's not necessarily that you haven't killed it, but these moulds and fungi spores float around in the air [so] they will come back."
Dr Taylor says cleaning the area every two to three weeks can stop build-up and "starve" the microbes.
