During sex, the nipples often become erect. This is a physiological response to sexual arousal. When a person feels excited, hormonal changes in the body cause the smooth muscles around the nipples to contract, making them harder and more sensitive. This reaction can also occur due to cold or other emotional stimuli.
However, responses can vary from person to person, and some people may not experience noticeable nipple erection during sex, which is completely normal.
