Nipples and the cold

Why do your nipples get hard when its old out?

Its because the nipples are rich is nerve ending which are very sensitive to stimuli eg touch. When its cold out more blood is pumped thoughout your body and to the nipples making them hard. Its very similar to when you're cold you get goosebumps and your hairs stand straight.

'Arrector pilori muscles which attach to every hair follicle in the skin contract the muscles generate heat in an effort to warm the body. the contraction is morecreates goosebumps on the skin. On the nipples it causes the skin to pull because obviously skin there is different somewhat.'