As every parent knows, nits are a common problem that affect all children, no matter how clean their hair.
But this truly gruesome video is the stuff of nightmares.
It shows what must surely be the worst case of head lice infestation of a child ever recorded.
In the video posted on YouTube – which has been viewed more than 4.5 million times - a woman is seen struggling to pull a nit comb through the child's wet hair.
After several minutes, the lice build up and the camera zooms in to show a cluster of writhing greyish-green parasites. Some escape on to the girl's neck and are put back into her hair so they can be combed out again.
It's enough to make your head itch just reading about it – but just wait until you've seen the video (for which we duly give advance warning).
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Dee Wright, whose Hairforce salon provides a specialist lice treatment, said the video was one of the worst cases she's seen.
She told the Mail: "We see infestations of that nature. We've even seen people with nests. That's where you've got so many lice they're clumping together.
"They're a big ball of lice fighting each other for survival."
Head lice are a common problem for school children, particularly between the ages of four and 11.
According to the NHS, around a third of pupils get head lice at some point every year, causing itching and a rash in some cases.
They're spread by head-to-head contact and climb between strands of children's hair, sometimes infesting parents and teachers.
An NHS spokesperson said: "A head lice infestation isn't the result of dirty hair or poor hygiene. All types of hair can be affected, regardless of its length and condition."
They can be treated with lotions or sprays, or by wet combing using a fine comb as seen in the video.
Lice hatch from eggs in around a week and grow to full size within 10 days, feeding on human blood.
The NHS warns that even when an infestation is treated, there is nothing to stop more lice coming back and constant checks are needed.
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