Science Monday: If Our Cells Replace Themselves, Why Do We Have Lifelong Scars?

Learn a new fact for the week: how rapidly does our body replace its cells? And if we constantly grow new skin, why do scars never fully vanish?

“Sorry, son, that scar is sticking with you for the rest of your life. Also, the doctors are baffled by your blurriness. They’re gonna name the condition after you.” Photo by Cristian Newman.

It’s a popular factoid, one that I remember hearing from multiple people, ever since I was a child:

“Our cells replace themselves every 7 years.”

Wow, it’s really inspiring. It’s also totally wrong, but Steven Hall’s a writer, not a scientist, so we can cut him a little slack. Source.

This factoid is often paired with all sorts of inspirational quotes. “If our cells replace themselves every 7 years, that means that you’re not the same person that you were seven years ago.”

It’s inspiring and uplifting, and we should all strive to improve ourselves — but if this fact is right, why do I still have a scar on my shoulder from a childhood injury?

Shouldn’t that scar have been replaced with new, fresh skin?

Or do we regrow scars?

The short answer is that this seven-year-replacement factoid is, sadly, incorrect. But we do know our cells regrow and replenish. How long does that take — and, back to the main point, why don’t our scars ever truly heal?