There can be a few reasons why:
Maybe your breast muscles are tightening
or if you can a lumo/bump on your breast that can be serious so if you do go get a mammogram done to make sure there can't be a tumor developing!
If you're a dude then it's most likely puberty but if your a woman you might wana get a pregnancy test
its a nipple erection
no, if u r cold your nipples tend to get hard. Women will most always get hard nipples when aroused and most men wont, but some do. if u r Mae and get hard nipples when aroused it doesnt mean theres anything wrong it just happens.
The same way you make a guy's nipples hard.
If you mean that they are always erect it is normal and nothing wrong with you.
Nipples that are really hard are referred to as being taut. They can also be called stiff or hard.
Yes, they do.
Hard.
Genetics,,, I once had A girlfriend that had nipples that were undetectable without your eyes.
wrong English man
We don't. They get hard when it's cold or some women get hard nipples when they are aroused. Same reasons some men have it actually.
on my phallus Nipples.
shes not your mum if she is asking you to rub her nipples that would be wrong.
Everyone is different. When you are young your nipples may be hard a lot of the time. As you get older your nipples tend to become hard only when you are cold, wet or sexually aroused.