How long it takes your body to regrow 19 types of cells and organs, from your skin to your skeleton
- The human body is in a constant state of regeneration, from the cells in our skeleton to the nails on our toes.
- But some cells are replaced more quickly than others, and some body parts never get replaced.
- The graphic below illustrates how cellular regeneration and regrowth happens in your body.
Human bodies change and regenerate throughout our lives.That process is easy to see if you watch babies' limbs grow and their bodies get bigger. It's also obvious when our toenails grow or healthy skin emerges after a burn peels away.
But less obvious systems of regrowth and rebirth in the body continue through adulthood. Dead skin cells constantly rise to the surface of our body, get sloughed off, then are replaced by new stem cells.
Some areas of the body take a long time to refresh themselves - for example, our fat-storage cells shift roughly once per decade, while we get fresh liver cells about once every 300 days.
Of course, your body doesn't simply throw away an entire liver's worth of cells on day 300 and create a brand new set on 301. Instead, it's more of an organic cycle, since liver cells continue to divide and regenerate long after they're mature.
Not every body part regenerates or changes, though. While the body's hairs are in a near constant state of growth, parts of the human brain and head pretty much finish developing at birth (like the lens of the eye that's helping you read this).
Not all members of the animal kingdom have the same processes of regeneration, of course. Some get wild with their techniques: freaked out geckos can drop their tails and grow new ones, spiders will grow replacement legs after one falls off or breaks, and deer shed their antlers and grow a new rack each year.
Meghan Bartels and Florence Fu contributed to an earlier version of this story.