It happens a lot, to both men and women. You've probably noticed that normally your nipples react to temperature and also when your aroused, or maybe even if it's just whenever anything touches them. But what causes your nipples to get hard? Different people have different levels of sensitivity and also different response levels.
Fun fact: During puberty I thought my nipples were broken. For whatever reason as a child all of the adult nipples I had seen had been erect, so when mine weren't erect all the time I assumed that they were defective and spent a lot of time in the locker room strategically changing to hide them. Nowadays, I not only realize that my nipples only being erect some of the time is completely normal, but also that nipples in whatever form are nothing to hide or be shy about. So in the free the nipple spirit, let's look a little more at what's actually happening when our nipples get hard.
I was weirded out when I realized the massive difference in the size of my areola when my nipples are erect versus when they're not. It turns out that's not unusual, but I still didn't understand how it could be such a huge change. Well maybe you've noticed that your nipples are wrinkly? That's got a lot to do with it. Apparently: "Epidermis in the unerected nipple shows wrinkles that increases the surface area. This wrinkles enables the surface to expand and becomes flat during erection." For all the details of how the muscles work, and to learn how to use the phrase 'nipple erection mechanism' in a sentence, try here. You'll be a hit at dinner parties I swear.
So that's how it happens, but why? Turns out your nipples are a little bit of a mystery, especially when it comes to how they react to temperature. As Forrest Wickman points out in Slate:
"No one knows, but it's probably for the same reason that cold gives you goose bumps. Low temperatures stimulate the tiny muscles attached to your hair follicles, which cause the hairs to stand on end. In other, hairier mammals, this process, known as the pilomotor reflex, can produce a layer of insulation. In humans, it seems to be vestigial. The areolae (the colored areas surrounding the nipples) also have smooth muscle cells that contract when stimulated, and cold weather can make the skin pucker inward while the nipples stick out."
So at some point the fact that our body could push out our hair and nipples helped us survive, but now there's not really a need.
Breastfeeding and Sexual Arousal
And while erect nipples do have a more obvious purpose in breastfeeding, helping to prompt the infant to suck, the erect nipple's purpose is still a mystery in its most famous role— sexual arousal. We all know that it happens. It is one of the elements of the "arousal" stage of the sexual response cycle (which includes desire, arousal, orgasm and resolution) and is described by Boston University School of Medicine as one of the "non-genital peripheral mechanisms"... not the best dirty talk I've ever heard, but certainly not the worst. It goes along with sweat and salivation as something that is going on in your body during sex outside of the obvious genital region. As it's a sign of arousal, it then becomes useful in recognizing arousal, but as we saw above there's a good chance you're not actually doing anything to turn her on... maybe she's just chilly. In either case, a lot of us find they're really fun to play with.
So we're not always exactly sure what's going on with our nipples. The fact that it's a really sensitive area, or, in science talk a place with "intense sensory innervation", may be one of the reasons it's so mysterious. Sometimes I realize that my nipples are out and proud at a moment I wouldn't expect and that may just be because they're reacting to something the rest of my body isn't aware of. But I'm not going to question it and, instead of being embarrassed or hiding them behind thick clothes, I'm ready to let them out. They're completely natural and it's not our job to hide them.
Images: iulia Pironea/Flickr; Giphy