Two years ago, I was staying with some friends who, incidentally, had our old dishwasher. It was a cheap slimline model which perfectly suited my husband and I as a couple with no kids (I think these days I’d go for a full-size model as we now cook with more plates and bigger pans).

I opened it up and was surprised to see that all the inside of the dishwasher, all the parts that should be white, were covered in this weird red stuff. It looked like the whole dishwasher was coated in those tea stains you get at the bottom of cups, it was the same reddish-brown colour but all over the dishwasher (except the metal bits). In the 6 years I’d known this dishwasher, I’d never seen anything like this before.

It turns out there is a special type of mould that affects dishwashers in one very specific situation. I was stunned to learn what had happened! My friends’ plates were too clean when they put them in the dishwasher! Can you believe that could be a problem?

So, yeah… The red stuff was a mould that grows in dishwashers if the dishes you put in them aren’t dirty enough. Here’s why:

When the dishwasher tablets don’t have enough to clean, they make the inside of your dishwasher more alkaline. This red-brown mould thrives in the damp, alkaline environment and is an absolute nuisance to remove once it sets in.

I found out how to get rid of the red mould in the dishwasher and here’s how I did it:

I started by doing the trusty “run the dishwasher through an empty load with a cup of white vinegar standing in the top rack”.

It didn’t work.

I was stunned. This always works.

The mould wasn’t shifting.

The first thing to know is that you can’t wipe this stuff off with a cloth. You need a hard scrubbing brush.

The second thing to know is that soaps and bleach are alkaline, like dishwasher tablets. If you try cleaning this stuff with any of those, you are basically feeding it, and it won’t go away.

So what you need is lemon juice or white vinegar. These are acids, which you might remember from high school science (or your biochem PhD… I’m not assuming anything, here) are the opposite of alkalines. When you have a mould that thrives in alkaline conditions, you need an acid.

However, it can’t be a strong acid because it could damage the dishwasher. So don’t use max strength toilet cleaner, even though it’s tempting to want to fight the mould explosion with something nuclear (or, more to the point, ionic).

Dip your hard scrubbing brush into your bowl of neat lemon juice or white vinegar and literally scrape the red mouldy stuff off each part of the dishwasher it has affected.

To accelerate the process, you can add salt (not bicarb) to the mixture for more scrubbing power.

Given how badly affected the dishwasher was, this took about an hour to scrub off every last bit of red mould, and I still couldn’t perfectly remove it from all the corners, but I was 8 months pregnant and very, very tired (also: nesting. I mean, who actually visits friends then obsessively cleans their dishwasher? Basically just pregnant people). I think partly I did it out of guilt, too, that this had been my dishwasher and I felt a bit responsible for it still. I didn’t want them to think I’d left them with a duff dishwasher.

Then run the dishwasher through an empty cycle with a cup of white vinegar, as above, and do this every week for a month to be sure the mould is really gone. Long-term, though, you need to stop washing your plates in the sink before dishwashering them. They need to be a bit dirty.

So that’s how to get rid of the red stuff coating your dishwasher shelves. It’s not a quick or easy fix, unfortunately, but if you find yourself in this situation, it’s absolutely worth doing.

You might be tempted to leave it as it looks more like a red staining than a mould growth, but here’s some of the health hazards of mould in your dishwasher:

• Respiratory problems
• Headaches
• Nausea
• Exhaustion and excessive tiredness
• Constant upset stomach (mimics IBS)

Mould can also be an irritant, especially if you have sensitive skin like I do. And you need to take care when cleaning your dishwasher out for the same reason. When mould is disturbed it can produce spores (which is how it reproduces).

Inhaling mould spores can cause an allergic reaction, with symptoms like sneezing, runny nose, red eyes, a skin rash, and it can also trigger asthma attacks (source: NHS website). So be sure to wear a mask if you’re working with a very mouldy dishwasher (I wish I’d done this) and wash your hands and arms thoroughly after working on your mouldy dishwasher, to remove any mould residue or spores that might have landed on your skin during the cleaning process.

Mould can be toxic and people have died from household mould exposure, so once you’ve identified mould in your dishwasher, you should absolutely take steps to get rid of it!

The other problem with mould is that it can spread really quickly. What was a bit of a brown stain (maybe you thought it was a tea stain) in the filter or blades of your dishwasher one week can completely overtake your whole dishwasher in as little as a few weeks! So keeping on top of a good dishwasher cleaning schedule is really important when you start to notice it getting a bit dirty!