As 5-year-old Ashlyn Blocker tackles the monkey bars with the same grit and determination as her fellow kindergarteners, a teacher keeps a careful eye on her, monitoring for any bumps or bruises sustained along the way.
When most of us are hurt, the body sounds an alarm. But that feeling is foreign to Ashlyn, who suffers from what's called congenital insensitivity to pain with anhidrosis, also known as CIPA, a rare genetic disorder affecting the nerve endings. She has no sense of extreme temperatures, and she can't feel pain -- though she can feel some non-painful sensations.
"One would think that a world without pain might be a blessing, but pain has been given to us to protect us," said Dr. Felicia Axelrod of NYU Medical Center.
John and Tara Blocker were unaware the condition even existed until they took the then-8-month-old baby to the doctor to treat an irritated eye. An examination revealed a massive scratch on her cornea.
"It got quiet and they were like, well, why isn't she feeling that?" Tara Blocker said. "That was the first question anybody asked. And of course … I don't even know."
At least 100 people worldwide are known to have CIPA and repeatedly suffer severe injuries, burns, cuts and fractures.
Family photos of Ashlyn reveal a swollen lip occurring after she mistakenly bit it, and a burned hand stemming from an appliance she did not know was extremely hot. On several occasions she's also knocked out teeth, which in the long run may have been a kind of blessing in disguise.
"She was biting her hands, biting her lip," said her father, John Blocker, "doing damage to her tongue, just biting various parts on her fingers, parts on her body.
At school, precautions are in place to keep Ashlyn injury free. Since the same condition makes her unable to sense outside temperature, she can't sweat. Therefore, there's always a cold bottle of water nearby.
After recess, Ashlyn reports to the nurse's office, where ABC News recently found the nurse looking for sand in her eyes. Her body got inspected from head to toe, and rid of residual sand that could have caused painful abrasions she wouldn't feel.
In a handful of cases, CIPA has proven fatal, because those afflicted are unable to feel symptoms of fever or life-threatening infections like appendicitis.
However, every case is different. So for Ashlyn, there's no telling what the future holds.
"It's really hard to look to the future, because we want the best for her," John Blocker said. "And we're hoping for the best."
Added Axelrod, "It's really the hope that eventually by understanding the gene and how the gene works that we will develop definitive therapies for these children."
ABC News' Diane Sawyer contributed to this report, which originally aired on Good Morning America on Nov. 8.