Dear Jennifer,
A cisgender woman's nipples get erect under two conditions: when she is cold, or when she is sexually aroused.
Makes me recall getting my senior picture took as a high school senior. When the photographer said, "think about your sweetheart," my nipples stood out like toothpaste caps! Was wearing a knit bra and over that, a knit dress. When I got my pictures back, I was devastated. Certainly didn't buy them, but they were in full color in the yearbook! LOL! 😕
Your friend,
Monica