Here’s a fun fact: we sweat out on average more than 98 litres per year, so imagine the build-up of bodily bacteria, dirt and dead skin that ends up on our pillows at night?

A cleaning expert in Australia has revealed we’re not changing our pillow cases as often as we should be.

[Read more: Your cleaning calendar: what you should be cleaning and when]

Shannon Lush told news.com.au: “If you’re showering once a day, you can wash your sheets weekly.

“However, pillowcases should be changed every second day without fail. It’s against your face, and your hair holds more dirt than anywhere else on the body. It’s like a mop.”

And if you’re suffering from an outbreak of blackheads, it could be down to you not changing your pillowcases – or washing your pillows – often enough.

Lush said: “Human skin is protein, and lots of nasties live in protein. You wouldn’t leave a steak in the middle of the bed, would you?”

How to wash and look after your pillowcases

Jane Robson, founder of luxury linen supplier The Fine Cotton Company, has the following advice…

1. Buy a spare set

“Pillow cases are vulnerable to staining from products such as make-up, moisturisers, hair dye as well as from bodily fluids – this is especially bad news for white pillows. I always advise to invest in a spare set of pillow cases so they can be rotated, even if you have only one duvet cover.”

2. Wash regularly at high temperatures

“The majority of our pillow cases are made from natural cotton, meaning they’re durable and can be washed at high temperatures, but always read the care label before washing items for the first time. Good quality natural materials won’t fade or wear with washing, so they can be laundered weekly at high temperatures and it won’t stop them from looking their best. All of our bedding is washable at 60 degrees - the temperature that kills dust mites and bacteria.” 

[Read more: 6 reasons you’re getting night sweats and what to do about them]

3. Measure laundry detergent carefully

“Be exact when measuring laundry cleaner, too much will cause a build-up of product and too little won’t clean the clothes thoroughly. Washing pillowcases regularly at 60 degrees will limit the build-up of dirt and detergent that will dull whites over time.” 

4. Use natural alternatives to clean them

“If you’re investing in organic fabrics there are some fabulous organic detergents on the market now. I’m a real advocate of natural products in the laundry process, so to bring a new lease of life to whites that have lost their sparkle, try including half a cup of white wine vinegar in with the wash. It’s a wonderful cleaning agent as the high acidity levels are naturally anti-bacterial, this neutralises odours and dissolves residual product.

“Another naturally acidic alternative to remove stains and whiten pillow cases is lemon juice – simply add a cup to your regular cycle and it will leave pillow cases smelling lovely and fresh.

“Baking soda will naturally keep whites white – it works in the opposite way to vinegar as it’s PH level is slightly alkaline, so as well as being very slightly abrasive to remove stains (but not enough to cause damage), it has a natural bleaching effect. Baking soda also absorbs odours and softens water, meaning you can use less product.”

5. Air them

“Fresh air and sunlight is a very effective way of killing germs, although it’s not always possible given the UK’s unpredictable weather, a hot iron over sheets and pillow cases will have the same effect and ensure any leftover bacteria is destroyed.”

How often do you change your pillowcases? Tell us in the comments box below