The star, made famous for her appearance on Googlebox alongside her mum and dad, revealed she was diagnosed with Bell's palsy at the age of 11, after she was knocked over by a car.
Scarlett, 25, explained in her autobiography Scarlett Says that the accident has left her with partial paralysis on one side of her face.
Reflecting on the moment she and her family realised she had the condition, Scarlett explained: 'I was doing a performance for my mum and dad - I used to put on little shows for them – when all of a sudden, my mouth just drooped and I remember standing in front of the mirror and just screaming.
'My eye dropped, I couldn't speak properly, I got all slurred, and my mum and dad thought I was putting it on.'
Scarlett with fellow camp mate, Carol Vorderman
Scarlett, who was a keen ballroom dancer when she was younger, continued: 'I was screaming so loud to try to get my mouth to go straight. I burst into tears and then they realised. It was awful.
Addressing how the condition has affected her since, the star explained that she needs the help of an eye mask to be able to sleep: 'I can't close my left eye properly. I have to sleep with a little eye mask and my mouth still goes to the side when I talk, although people don't really notice.
'Sometimes if I'm tired, my left eye feels a little bit twitchy, but I don't get pain or slur my words. I don't feel sorry for myself, as there are so many worse afflictions people can get.'
Scarlett has already become a huge favourite on the show
Scarlett, whose recent weight loss journey has inspired thousands of fans, was exempt from Wednesday evening's Great Ascent trial, prompting speculation that her exclusion from the task related to her condition.
According to the NHS, Bell's palsy is 'a condition that causes temporary weakness or paralysis of the muscles in one side of the face', and is the most common cause of facial paralysis.