The 20-year-old singer spoke about her Tourette’s on the most recent episode of Netflix series My Next Guest Needs No Introduction with David Letterman. During the interview, the star appeared to turn her head and open her mouth. Letterman asks, “What’s going on? The fly?” Eilish replies: “No, I’m ticcing.”

Letterman apologises and Eilish says “the lights” brought it on.

She explains: “If you film me for long enough, you’re going to see lots of tics.”

She adds: “I don’t care. It’s really weird, I haven’t talked about it at all.”

Tourette’s syndrome is a condition that causes a person to make involuntary sounds and movements called tics, the NHS explains.

Tics are the main symptom and usually appear in childhood between the ages of two and 14.

The health body states: “People with Tourette’s syndrome have a combination of physical and vocal tics.”

Examples of tics include blinking, jerking of the head or limbs, tongue clicking and swearing.

But swearing is considered rare, only affecting about one in 10 people with Tourette’s.

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Letterman asks Eilish if she’s comfortable discussing her Tourette’s and she happily answers: “The most common way people react is they laugh, because they think that I’m trying to be funny.

“They think I’m going like [imitates tic] as a funny move, and so they go, ‘Ha’. And I’m always left incredibly offended by that.

“Or they go like [looks behind her] ‘what?’… and then I go, ‘I have Tourette’s’.”

Letterman says he had the same reaction and thought he’d “said something to p*** her off”.

But the singer replies: “What’s funny is so many people have it that you would never know.

“A couple of artists have come forward and said, ‘I’ve always had Tourette’s.’ And I’m not going to out them because they don’t want to talk about it but that was always actually really interesting to me.”

Letterman says: ““I hope to God what we’ve done here didn’t exacerbate this. I know nothing about this.”

But Eilish replies: “Not at all. I actually really love answering questions about it because it’s very, very interesting. And I am incredibly confused by it, and I don’t get it.”

The singer confirmed she had Tourette’s after videos of her tics began to surface online.

At the time, she wrote on her Instagram story: “I’ve never mentioned [my Tourette Syndrome] on the internet because nobody thinks I’m deadass.

“As well as the fact I’ve just never wanted people to think of Tourette’s every time they think of me.”

She went on to mention: “I’ve taught myself ways of suppressing my tics and certain techniques to help [reduce] them when I don’t want to be distracting in certain situations.

“Wasn’t planning on talking about this on here maybe ever, but it’s gotten to a point.”

You should contact a GP if you or your child start having tics.