There is a phenomenon on how far we can push ourselves with pain. We do so much to our bodies on a daily basis and sometimes put it through pain for some reward. Piercings, tattoos, exercising, conceiving a child (for women obviously), cosmetic surgeries, the 'Pain Olympics'. Whether it be for appearance, health reasons, the want for a child, or fame, the human race has gone to extreme lengths when it comes to pain.
Everyone's pain tolerance varies from person to person. Many people think it is based off of gender or genetics but there is no true answer... yet. There have been a few studies on human pain thresholds and what causes it. There is a good argument for gender as well as genetics, but science can't claim one for sure. Here are some sites to read further about each theory.
But what if you couldn't feel pain at all? Not even extreme temperatures? There is something called Congenital Insensitivity to Pain with Anhidrosis that causes you to have the inability to feel pain, temperature, or to sweat accordingly. It's caused by a genetic mutation usually caught in infancy. People with CIPA are more susceptible to injury, hypothermia, and other life threating conditions and they wouldn't even be aware enough to get help.
It is unknown how many people have CIPA. There is also no known cure, but there are a few treatments using a chemical naloxone. Not many people live past the first few years of life because they cannot sweat which leads to hypothermia. Two really great sites that explain this CIPA in greater detail are:
An episode of House was aired in season three of a girl who had CIPA. It was an interesting episode and a good look into how someone with CIPA copes with the condition. It got a little medically inaccurate to wards the end of the episode, but still very entertaining! Not many clips were available due to copyright laws, but here is a short trailer. Try to catch the episode!