Why do nipples change in the cold?

The main reason nipples get hard in cold weather is due to the contraction of the muscles beneath the skin. When muscles contract, they shorten, which causes the nipple to become erected. This is a natural reflex that helps to keep the body warm by preserving heat and protecting the sensitive nipple tissue from damage. Another possible reason for nipple hardness in cold weather is due to the release of hormones such as adrenaline, which can cause muscles to contract. Additionally, cold temperatures can cause blood vessels to constrict, which can restrict blood flow to the nipples and cause them to become pale or even bluish in color.