A doctor has revealed the truth about those gross yellow stains we get on our pillows – stressing the mark is a sign it's time to get a new one.
Dr Karan Raj, an NHS surgeon in the UK, has amassed three million followers on TikTok explaining weird and wonderful medical situations in easy to understand videos.
He's answered questions about sleep conditions, broken down the "mind-blowing" placebo effect and explained why chemo causes hair loss.
But Raj's video titled "Change your pillows" has had a lasting effect on viewers, with some declaring it has left them "shocked".
"You need to change your pillows at least every two years", Raj explains.
"The average person sheds about 4kg of skin every year. Most of that ends up on your bed or pillow – a feast for microscopic dust mites."
He went on to explain a dust mite leaves about 20 droppings a day which amounts to a lot when multiplied by the hundreds of mites living on your pillow.
"A build up of dust mite faeces can cause breathing and allergy-type symptoms."
Raj also explained the mystery surrounding the "nasty" yellow spots and patches that develop on pillows over time, revealing they're caused by a build-up of sweat and oil from your body.
"That moisture can breed mould and bacteria," he said.
And last – but definitely not least – Raj shared a simple trick to test whether or not your pillow was "dead" and ready for the bin.
"If you can fold your pillow in half and it doesn't spring back, that pillow is dead," he said.
"It's no longer helping to keep your neck and spine in alignment, causing neck and shoulder pain."
The video has been viewed over 1.2 million times since it was shared in February, proving just how much we care about sleep.
Many stated in the comments they had "pillows older than me", while others said: "I wish I didn't see this video."
"Oh that's why it's hard to breathe," one person wrote.
"I've been using the same pillow for 11 years," another confessed.
"Really what I wanted to see before I go to bed with my 20-year-old pillow. I know it's bad but I need it," one woman said.
Others asked if they could wash their pillows or if pillow cases made much difference. While many admitted to checking if their pillows folded after watching the clip.
Dust mites can trigger asthma, eczema and other health conditions – but they are not the only bug lurking in our pillows. A study that examined 10 pillows that had been in family homes for between 18 months and 20 years found they were all contaminated with "numerous fungi".
This can cause health issues, especially if you're asthmatic or have a weakened immune system.
Hands up who is going to get new pillows this weekend?