Does Your Body Replace Itself Every 7 Years?
It's a beautiful idea, when you think about it: your body replaces all of its cells every 7 years, so in that time you've left the old you behind and become a completely different person. Unfortunately, it's just not true. No one knows where the 7-year myth came from, but even if it was a rough average of every cell's lifespan, it would still be wrong. Some parts of you remain for your entire life. The cells on the inner lens of your eye have been there since you were a fetus. Your tooth enamel is never replaced, and neither are the neurons in your cerebral cortex. Luckily, neurons in other parts of your brain do regrow. As do other parts of your body: colon cells, for instance, refresh after only four days, and you get an entirely new skin every 2-3 weeks. White blood cells take more than a year to regenerate, and it takes an average of 10 years to grow an entirely new skeleton.
from Brain Stuff
Key Facts In This Video
Your body mostly replaces itself every 7–15 years. Some parts are never replaced, and some parts are replaced much more quickly. (0:19)
The organs that work the hardest have the fastest changeover. You get a whole new skin every 2-4 weeks, red blood cells last only half the year, and your liver renews itself at least once every couple years. (0:37)
Some parts of your body stay with you for life. The cells on the inner lens of your eye were formed when you were an embryo. Tooth enamel never regrows, and evidence indicates that you can't regrow the neurons of the cerebral cortex. (1:14)