"If you cut your nipple off, will it grow back?"

So I'm playing TF2 last night, when I hear the following question come through my headphones:

LOLWHUT.  (Aka. Ursulav's "Biting Pear of Salamanca")

Luckily for everyone involved, the people I play with are an intelligent group and quickly provided the correct answer to this most peculiar of inquiries.

"No, man, it would just scar over." "Duh, you would have to, like, steal one." "The body doesn't know how to regrow limbs and stuff like that after you're out of your mom's fetus." "'Fetus'?" "I mean uterus. Shut up. You need stem cells." "Oh, so we COULD regrow one now, couldn't we?"

I love you guys, and technically you are correct, but let's look over why you are correct.

"It would just scar over."
If you were to cut off your nipple, and just let it alone, the area would simply scar over. Nipples, in both men and women, are structurally distinct from the rest of your skin; composed of not just skin, but glandular and fatty tissue as well. If you were to cut it off, you'd only grow scar tissue. Nipple removal is actually a practiced type of body modification in certain communities, though it does carry a number of inherent risks. I wouldn't recommend it.

"Duh, you would have to, like, steal one."
Not totally true, but theoretically possible. There are methods, for example, that spare the nipple and allow women to retain them after a mastectomy. It may also be possible to grow pigmented skin cells that can later be transfer to simulate a nipple after you've lost one.

"The body doesn't know how to regrow limbs and shit like that after you're out of your mom's fetus."
This one is REALLY complicated, and could lead to an entire series on fetal development, but today, we're just going to focus on the body part in question. Until you are 6 weeks old, all humans begin development looking the same, it isn't until that point in time that any male-specific characteristics begin to emerge. So, why do men have nipples? Because women do. After 6 weeks, male fetuses (usually) begin producing enough testosterone to halt breast development.  HOWEVER, if you were to cut off a fetus' nipple (you horrible horrible person, you) it still wouldn't grow back. Just as a fetus' ear wouldn't grow back (seriously, what is WRONG with you?), because...

"You need stem cells."
There are 5 types of stem cells you all need to know about.

1. Totipotent cells can divide to become ANY cell of an organism. Potential-humans are made of totipotent cells until they have become a 16-cell ball. After which the bundle becomes a morula which divides itself into differentiated cells.
2. Pluripotent cells can turn into all three of three different layers of cells which eventually turn into a fetus. I.e. They can become the endoderm (interior stomach lining, gastrointestinal tract, the lungs), mesoderm (muscle, bone, blood, urogenital), or ectoderm (epidermal tissues and nervous system), but they can't do jack to help you live in the womb.
3. Multipotent cells can divide indefinitely and can become a number of different cells of the same "type". For example, a blood stem cell can become a red blood cell, or a white blood cell, but it can't become a brain cell. Although, there may be ways to mess with this process.
4. Olgopotent cells can only divide a couple times, but they still have the potential to turn into different things if you push them. (e.g. Bone marrow stromal cells can turn into bone marrow, cartilage or fat cells.)
5. Unipotent cells can only turn into one thing. Livers, for example, can regrow themselves because liver cells are unipotent. Liver cells can only be liver cells.

"So we COULD regrow one?"
What's so great about stem cells? They're toti-and-pluri-potent. With the proper techniques and growing environments, you can goad them into becoming what you want them to be, allowing people the chance to grow replacement-bits using their own cells. Ideally, this would mean you could regrow the individual bits of your missing nipple, and put them together to build a new one.

But you know what?

That would be really freaking complicated.


It would be easier to regrow a heart, or an ear. You know, something that is mostly one thing, rather than a structure built of different things. You have to BUILD a nipple.

Sheesh dude. Just don't cut your nipple off. Ok?