Like any other toddler, Ben Whittaker has had his fair share of bumps and bruises. The difference is he doesn't feel any pain.
Ben once pulled a tooth out without feeling any pain
The 17-month-old from Royston, Yorkshire, is only the 33rd person ever to be diagnosed with the condition.
When Ben fractured his heel bone, he ran around as if nothing was wrong, and he shed no tears after pulling out a tooth.
His parents, Wayne and Joanne, say they cannot let him out of their sight.
The couple first noticed that Ben was different to other toddlers when he was nine months old. He took a hot chip from his father's plate and blistered three fingers - without showing any signs of distress.
The health visitor suggested there may be something unusual about the way Ben dealt with pain.
The toddler then broke his heel bone while he was playing at home.
When he was taken to hospital for treatment, doctors saw Ben running around despite having a plaster cast on his foot.
Wayne Whittaker told the BBC News Website the doctors had said Ben would have been "in agony" if he had been an adult.
'It makes things difficult'
After a series of tests at Sheffield Children's Hospital, Ben was diagnosed as having congenital indifference to pain, an incredibly rare condition.
Experts have suggested it could be caused by the failure of a substance called betaendorphin, which occurs naturally in the body and modulates pain sensations.
Mr Whittaker said: "It was a case of putting two and two together. He didn't cry when he banged his head, and he didn't cry when he had his inoculations.
"He may feel no pain at all, or he may feel pain differently to other children. We won't know until he can communicate."
He said the condition was becoming more of a problem as Ben got older.
"When he was a baby, it didn't really affect him. But when he started to crawl, and now he can walk and run, it does. He keeps banging his head, but it doesn't bother him."
Ben is healthy in all other ways, and has a toddler's natural curiosity - meaning he is at the stage where he is keen to climb and explore.
Mr Whittaker said the couple were terrified Ben would put his hand into the fire or burn himself on the radiator - but not feel anything.
The couple have another child, Katie, who is three months old, and Wayne said it could be difficult for his wife Joanne to keep an eye on Ben.
Mr Whittaker added: "It obviously makes things difficult. But you just can't let him out of your sight."
Doctors have told them there is nothing they can do to alleviate Ben's condition, and it is something he will have to live with. They have been warned it is possible Katie will also be affected.